Publications by authors named "Ivan Williams"

28 Publications

  • Page 1 of 1

Measuring the dose in bone for spine stereotactic body radiotherapy.

Phys Med 2021 Apr 25;84:265-273. Epub 2021 Mar 25.

Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia.

Purpose: Current quality assurance of radiotherapy involving bony regions generally utilises homogeneous phantoms and dose calculations, ignoring the challenges of heterogeneities with dosimetry problems likely occurring around bone. Anthropomorphic phantoms with synthetic bony materials enable realistic end-to-end testing in clinical scenarios. This work reports on measurements and calculated corrections required to directly report dose in bony materials in the context of comprehensive end-to-end dosimetry audit measurements (63 plans, 6 planning systems).

Materials And Methods: Radiochromic film and microDiamond measurements were performed in an anthropomorphic spine phantom containing bone equivalent materials. Medium dependent correction factors, k, were established using 6 MV and 10 MV Linear Accelerator Monte Carlo simulations to account for the detectors being calibrated in water, but measuring in regions of bony material. Both cortical and trabecular bony material were investigated for verification of dose calculations in dose-to-medium (D) and dose-to-water (D) scenarios.

Results: For D calculations, modelled correction factors for cortical and trabecular bone in film measurements, and for trabecular bone in microDiamond measurements were 0.875(±0.1%), 0.953(±0.3%) and 0.962(±0.4%), respectively. For D calculations, the corrections were 0.920(±0.1%), 0.982(±0.3%) and 0.993(±0.4%), respectively. In the audit, application of the correction factors improves the mean agreement between treatment plans and measured microDiamond dose from -2.4%(±3.9%) to 0.4%(±3.7%).

Conclusion: Monte Carlo simulations provide a method for correcting the dose measured in bony materials allowing more accurate comparison with treatment planning system doses. In verification measurements, algorithm specific correction factors should be applied to account for variations in bony material for calculations based on D and D.
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http://dx.doi.org/10.1016/j.ejmp.2021.03.011DOI Listing
April 2021

A comparison of IROC and ACDS on-site audits of reference and non-reference dosimetry.

Med Phys 2019 Dec 25;46(12):5878-5887. Epub 2019 Oct 25.

Australian Clinical Dosimetry Service, ARPANSA, Melbourne, Australia.

Purpose: Consistency between different international quality assurance groups is important in the progress toward similar standards and expectations in radiotherapy dosimetry around the world, and in the context of consistent clinical trial data from international trial participants. This study compares the dosimetry audit methodology and results of two international quality assurance groups performing a side-by-side comparison at the same radiotherapy department, and interrogates the ability of the audits to detect deliberately introduced errors.

Methods: A comparison of the core dosimetry components of reference and non-reference audits was conducted by the Imaging and Radiation Oncology Core (IROC, Houston, USA) and the Australian Clinical Dosimetry Service (ACDS, Melbourne, Australia). A set of measurements were conducted over 2 days at an Australian radiation therapy facility in Melbourne. Each group evaluated the reference dosimetry, output factors, small field output factors, percentage depth dose (PDD), wedge, and off-axis factors according to their standard protocols. IROC additionally investigated the Electron PDD and the ACDS investigated the effect of heterogeneities. In order to evaluate and compare the performance of these audits under suboptimal conditions, artificial errors in percentage depth dose (PDD), EDW, and small field output factors were introduced into the 6 MV beam model to simulate potential commissioning/modeling errors and both audits were tested for their sensitivity in detecting these errors.

Results: With the plans from the clinical beam model, almost all results were within tolerance and at an optimal pass level. Good consistency was found between the two audits as almost all findings were consistent between them. Only two results were different between the results of IROC and the ACDS. The measurements of reference FFF photons showed a discrepancy of 0.7% between ACDS and IROC due to the inclusion of a 0.5% nonuniformity correction by the ACDS. The second difference between IROC and the ACDS was seen with the lung phantom. The asymmetric field behind lung measured by the ACDS was slightly (0.3%) above the ACDS's pass (optimal) level of 3.3%. IROC did not detect this issue because their measurements were all assessed in a homogeneous phantom. When errors were deliberately introduced neither audit was sensitive enough to pick up a 2% change to the small field output factors. The introduced PDD change was flagged by both audits. Similarly, the introduced error of using 25° wedge instead of 30° wedge was detectible in both audits as out of tolerance.

Conclusions: Despite different equipment, approach, and scope of measurements in on-site audits, there were clear similarities between the results from the two groups. This finding is encouraging in the context of a global harmonized approach to radiotherapy quality assurance and dosimetry audit.
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http://dx.doi.org/10.1002/mp.13800DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6916618PMC
December 2019

Remote beam output audits: a global assessment of results out of tolerance.

Phys Imaging Radiat Oncol 2018 Jul 16;7:39-44. Epub 2018 Sep 16.

Australian Clinical Dosimetry Service, ARPANSA, Melbourne, Australia.

Background And Purpose: Remote beam output audits, which independently measure an institution's machine calibration, are a common component of independent radiotherapy peer review. This work reviews the results and trends of these audit results across several organisations and geographical regions.

Materials And Methods: Beam output audit results from the Australian Clinical Dosimetry Services, International Atomic Energy Agency, Imaging and Radiation Oncology Core, and Radiation Dosimetry Services were evaluated from 2010 to the present. The rate of audit results outside a +/-5% tolerance was evaluated for photon and electron beams as a function of the year of irradiation and nominal beam energy. Additionally, examples of confirmed calibration errors were examined to provide guidance to clinical physicists and auditing bodies.

Results: Of the 210,167 audit results, 1323 (0.63%) were outside of tolerance. There was a clear trend of improved audit performance for more recent dates, and while all photon energies generally showed uniform rates of results out of tolerance, low (6 MeV) and high (≥18 MeV) energy electron beams showed significantly elevated rates. Twenty nine confirmed calibration errors were explored and attributed to a range of issues, such as equipment failures, errors in setup, and errors in performing the clinical reference calibration. Forty-two percent of these confirmed errors were detected during ongoing periodic monitoring, and not at the time of the first audit of the machine.

Conclusions: Remote beam output audits have identified, and continue to identify, numerous and often substantial beam calibration errors.
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http://dx.doi.org/10.1016/j.phro.2018.08.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6927685PMC
July 2018

Dosimetric end-to-end tests in a national audit of 3D conformal radiotherapy.

Phys Imaging Radiat Oncol 2018 Apr 24;6:5-11. Epub 2018 Apr 24.

Australian Clinical Dosimetry Service (ACDS), Australian Radiation Protection and National Safety Agency (ARPANSA), 619 Lower Plenty Road, Yallambie, VIC 3085, Australia.

Background And Purpose: Independent dosimetry audits improve quality and safety of radiation therapy. This work reports on design and findings of a comprehensive 3D conformal radiotherapy (3D-CRT) Level III audit.

Materials And Methods: The audit was conducted as onsite audit using an anthropomorphic thorax phantom in an end-to-end test by the Australian Clinical Dosimetry Service (ACDS). Absolute dose point measurements were performed with Farmer-type ionization chambers. The audited treatment plans included open and half blocked fields, wedges and lung inhomogeneities. Audit results were determined as Pass Optimal Level (deviations within 3.3%), Pass Action Level (greater than 3.3% but within 5%) and Out of Tolerance (beyond 5%), as well as Reported Not Scored (RNS). The audit has been performed between July 2012 and January 2018 on 94 occasions, covering approximately 90% of all Australian facilities.

Results: The audit pass rate was 87% (53% optimal). Fifty recommendations were given, mainly related to planning system commissioning. Dose overestimation behind low density inhomogeneities by the analytical anisotropic algorithm (AAA) was identified across facilities and found to extend to beam setups which resemble a typical breast cancer treatment beam placement. RNS measurements inside lung showed a variation in the opposite direction: AAA under-dosed a target beyond lung and over-dosed the lung upstream and downstream of the target. Results also highlighted shortcomings of some superposition and convolution algorithms in modelling large angle wedges.

Conclusions: This audit showed that 3D-CRT dosimetry audits remain relevant and can identify fundamental global and local problems that also affect advanced treatments.
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http://dx.doi.org/10.1016/j.phro.2018.03.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7807562PMC
April 2018

Survey of 5 mm small-field output factor measurements in Australia.

J Appl Clin Med Phys 2018 Mar 25;19(2):329-337. Epub 2018 Jan 25.

Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Vic, Australia.

The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) held a comparison exercise in April 2016 where participants came to ARPANSA and measured the output factor of a nominal 5 mm cone attached to the ARPANSA Elekta Synergy (Elekta, Crawley, UK) linear accelerator. The goal of the exercise was to compare the consistency and methods used by independent medical physicists in measuring small-field output factors. ARPANSA provided a three-dimensional scanning tank for detector setup and positioning, but the participants were required to measure the output factor with their own detectors. No information regarding output factors previously measured was supplied to participants to make each result as independent as possible. Fifteen groups travelled to ARPANSA bringing a wide range of detectors and methods. A total of 30 measurements of the output factor were made. The standard deviation of the measurements (excluding one expected outlier from an uncorrected ionization chamber measurement) was 3.6%. The results provide an insight into the consistency of small-field dosimetry being performed in Australia and New Zealand at the present time.
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http://dx.doi.org/10.1002/acm2.12259DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5849830PMC
March 2018

Methodology to assess quality of estimated disturbances in active disturbance rejection control structure for mechanical system.

ISA Trans 2017 Sep 27;70:238-247. Epub 2017 May 27.

Mexicali Research and Technology Center, Honeywell, Del Oro 1755, Mexicali, Mexico.

A methodology to assess the quality of estimation of disturbances in mechanical systems, by state observers, in the control structure with active compensation of disturbances (ADRC) is presented. Evaluation is carried out by four performance indices that depend on the steady-state error between reference signals and output of the plant. These indices are related with the accuracy and precision of the closed loop system in the sense of norms L and L, for a set of reference signals representing the typical operating conditions of the mechanism. The effectiveness of the methodology is illustrated with the quality assessment of the estimated disturbance of five state observers to control of a simple pendulum and validated on a SCARA robot arm.
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http://dx.doi.org/10.1016/j.isatra.2017.05.013DOI Listing
September 2017

National dosimetric audit network finds discrepancies in AAA lung inhomogeneity corrections.

Phys Med 2015 Jul 23;31(5):435-41. Epub 2015 Apr 23.

Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia; School of Applied Science, RMIT University, Melbourne, Australia.

This work presents the Australian Clinical Dosimetry Service's (ACDS) findings of an investigation of systematic discrepancies between treatment planning system (TPS) calculated and measured audit doses. Specifically, a comparison between the Anisotropic Analytic Algorithm (AAA) and other common dose-calculation algorithms in regions downstream (≥2cm) from low-density material in anthropomorphic and slab phantom geometries is presented. Two measurement setups involving rectilinear slab-phantoms (ACDS Level II audit) and anthropomorphic geometries (ACDS Level III audit) were used in conjunction with ion chamber (planar 2D array and Farmer-type) measurements. Measured doses were compared to calculated doses for a variety of cases, with and without the presence of inhomogeneities and beam-modifiers in 71 audits. Results demonstrate a systematic AAA underdose with an average discrepancy of 2.9 ± 1.2% when the AAA algorithm is implemented in regions distal from lung-tissue interfaces, when lateral beams are used with anthropomorphic phantoms. This systemic discrepancy was found for all Level III audits of facilities using the AAA algorithm. This discrepancy is not seen when identical measurements are compared for other common dose-calculation algorithms (average discrepancy -0.4 ± 1.7%), including the Acuros XB algorithm also available with the Eclipse TPS. For slab phantom geometries (Level II audits), with similar measurement points downstream from inhomogeneities this discrepancy is also not seen.
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http://dx.doi.org/10.1016/j.ejmp.2015.04.002DOI Listing
July 2015

Long term OSLD reader stability in the ACDS level one audit.

Australas Phys Eng Sci Med 2015 Mar 14;38(1):151-6. Epub 2014 Dec 14.

Australian Clinical Dosimetry Service, Yallambie, VIC, 3085, Australia,

The Australian Clinical Dosimetry Service (ACDS) has demonstrated the capacity to perform a basic dosimetry audit on all radiotherapy clinics across Australia. During the ACDS's three and a half year trial the majority of the audits were performed using optically stimulated luminescence dosimeters (OSLD) mailed to facilities for exposure to a reference dose, and then returned to the ACDS for analysis. This technical note investigates the stability of the readout process under the large workload of the national dosimetry audit. The OSLD readout uncertainty contributes to the uncertainty of several terms of the dose calculation equation and is a major source of uncertainty in the audit. The standard deviation of four OSLD readouts was initially established at 0.6 %. Measurements over 13 audit batches--each batch containing 200-400 OSLDs--showed variability (0.5-0.9 %) in the readout standard deviation. These shifts have not yet necessitated a change to the audit scoring levels. However, a standard deviation in OSLD readouts greater than 0.9 % will change the audit scoring levels. We identified mechanical wear on the OSLD readout adapter as a cause of variability in readout uncertainty, however, we cannot rule out other causes. Additionally we observed large fluctuations in the distribution of element correction factors (ECF) for OSLD batches. We conclude that the variability in the width of the ECF distribution from one batch to another is not caused by variability in readout uncertainty, but rather by variations in the OSLD stock.
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http://dx.doi.org/10.1007/s13246-014-0320-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4445253PMC
March 2015

A 2D ion chamber array audit of wedged and asymmetric fields in an inhomogeneous lung phantom.

Med Phys 2014 Oct;41(10):101712

Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia and School of Applied Science, RMIT University, Melbourne 3000, Australia.

Purpose: The Australian Clinical Dosimetry Service (ACDS) has implemented a new method of a nonreference condition Level II type dosimetric audit of radiotherapy services to increase measurement accuracy and patient safety within Australia. The aim of this work is to describe the methodology, tolerances, and outcomes from the new audit.

Methods: The ACDS Level II audit measures the dose delivered in 2D planes using an ionization chamber based array positioned at multiple depths. Measurements are made in rectilinear homogeneous and inhomogeneous phantoms composed of slabs of solid water and lung. Computer generated computed tomography data sets of the rectilinear phantoms are supplied to the facility prior to audit for planning of a range of cases including reference fields, asymmetric fields, and wedged fields. The audit assesses 3D planning with 6 MV photons with a static (zero degree) gantry. Scoring is performed using local dose differences between the planned and measured dose within 80% of the field width. The overall audit result is determined by the maximum dose difference over all scoring points, cases, and planes. Pass (Optimal Level) is defined as maximum dose difference ≤3.3%, Pass (Action Level) is ≤5.0%, and Fail (Out of Tolerance) is >5.0%.

Results: At close of 2013, the ACDS had performed 24 Level II audits. 63% of the audits passed, 33% failed, and the remaining audit was not assessable. Of the 15 audits that passed, 3 were at Pass (Action Level). The high fail rate is largely due to a systemic issue with modeling asymmetric 60° wedges which caused a delivered overdose of 5%-8%.

Conclusions: The ACDS has implemented a nonreference condition Level II type audit, based on ion chamber 2D array measurements in an inhomogeneous slab phantom. The powerful diagnostic ability of this audit has allowed the ACDS to rigorously test the treatment planning systems implemented in Australian radiotherapy facilities. Recommendations from audits have led to facilities modifying clinical practice and changing planning protocols.
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http://dx.doi.org/10.1118/1.4896097DOI Listing
October 2014

Angular dependence of the response of the nanoDot OSLD system for measurements at depth in clinical megavoltage beams.

Med Phys 2014 Jun;41(6):061712

Australian Clinical Dosimetry Service, 619 Lower Plenty Road, Yallambie, VIC 3085, Australia and School of Applied Sciences, Royal Melbourne Institute of Technology (RMIT) University, GPO Box 2476, Melbourne, VIC 3000, Australia.

Purpose: The purpose of this investigation was to assess the angular dependence of a commercial optically stimulated luminescence dosimeter (OSLD) dosimetry system in MV x-ray beams at depths beyond d(max) and to find ways to mitigate this dependence for measurements in phantoms.

Methods: Two special holders were designed which allow a dosimeter to be rotated around the center of its sensitive volume. The dosimeter's sensitive volume is a disk, 5 mm in diameter and 0.2 mm thick. The first holder rotates the disk in the traditional way. It positions the disk perpendicular to the beam (gantry pointing to the floor) in the initial position (0°). When the holder is rotated the angle of the disk towards the beam increases until the disk is parallel with the beam ("edge on," 90°). This is referred to as Setup 1. The second holder offers a new, alternative measurement position. It positions the disk parallel to the beam for all angles while rotating around its center (Setup 2). Measurements with five to ten dosimeters per point were carried out for 6 MV at 3 and 10 cm depth. Monte Carlo simulations using GEANT4 were performed to simulate the response of the active detector material for several angles. Detector and housing were simulated in detail based on microCT data and communications with the manufacturer. Various material compositions and an all-water geometry were considered.

Results: For the traditional Setup 1 the response of the OSLD dropped on average by 1.4% ± 0.7% (measurement) and 2.1% ± 0.3% (Monte Carlo simulation) for the 90° orientation compared to 0°. Monte Carlo simulations also showed a strong dependence of the effect on the composition of the sensitive layer. Assuming the layer to completely consist of the active material (Al2O3) results in a 7% drop in response for 90° compared to 0°. Assuming the layer to be completely water, results in a flat response within the simulation uncertainty of about 1%. For the new Setup 2, measurements and Monte Carlo simulations found the angular dependence of the dosimeter to be below 1% and within the measurement uncertainty.

Conclusions: The dosimeter system exhibits a small angular dependence of approximately 2% which needs to be considered for measurements involving other than normal incident beams angles. This applies in particular to clinical in vivo measurements where the orientation of the dosimeter is dictated by clinical circumstances and cannot be optimized as otherwise suggested here. When measuring in a phantom, the proposed new setup should be considered. It changes the orientation of the dosimeter so that a coplanar beam arrangement always hits the disk shaped detector material from the thin side and thereby reduces the angular dependence of the response to within the measurement uncertainty of about 1%. This improvement makes the dosimeter more attractive for clinical measurements with multiple coplanar beams in phantoms, as the overall measurement uncertainty is reduced. Similarly, phantom based postal audits can transition from the traditional TLD to the more accurate and convenient OSLD.
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http://dx.doi.org/10.1118/1.4875698DOI Listing
June 2014

Remote auditing of radiotherapy facilities using optically stimulated luminescence dosimeters.

Med Phys 2014 Mar;41(3):032102

Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia and School of Applied Science, RMIT University, Melbourne 3000, Australia.

Purpose: On 1 July 2012, the Australian Clinical Dosimetry Service (ACDS) released its Optically Stimulated Luminescent Dosimeter (OSLD) Level I audit, replacing the previous TLD based audit. The aim of this work is to present the results from this new service and the complete uncertainty analysis on which the audit tolerances are based.

Methods: The audit release was preceded by a rigorous evaluation of the InLight® nanoDot OSLD system from Landauer (Landauer, Inc., Glenwood, IL). Energy dependence, signal fading from multiple irradiations, batch variation, reader variation, and dose response factors were identified and quantified for each individual OSLD. The detectors are mailed to the facility in small PMMA blocks, based on the design of the existing Radiological Physics Centre audit. Modeling and measurement were used to determine a factor that could convert the dose measured in the PMMA block, to dose in water for the facility's reference conditions. This factor is dependent on the beam spectrum. The TPR20,10 was used as the beam quality index to determine the specific block factor for a beam being audited. The audit tolerance was defined using a rigorous uncertainty calculation. The audit outcome is then determined using a scientifically based two tiered action level approach. Audit outcomes within two standard deviations were defined as Pass (Optimal Level), within three standard deviations as Pass (Action Level), and outside of three standard deviations the outcome is Fail (Out of Tolerance).

Results: To-date the ACDS has audited 108 photon beams with TLD and 162 photon beams with OSLD. The TLD audit results had an average deviation from ACDS of 0.0% and a standard deviation of 1.8%. The OSLD audit results had an average deviation of -0.2% and a standard deviation of 1.4%. The relative combined standard uncertainty was calculated to be 1.3% (1σ). Pass (Optimal Level) was reduced to ≤2.6% (2σ), and Fail (Out of Tolerance) was reduced to >3.9% (3σ) for the new OSLD audit. Previously with the TLD audit the Pass (Optimal Level) and Fail (Out of Tolerance) were set at ≤4.0% (2σ) and >6.0% (3σ).

Conclusions: The calculated standard uncertainty of 1.3% at one standard deviation is consistent with the measured standard deviation of 1.4% from the audits and confirming the suitability of the uncertainty budget derived audit tolerances. The OSLD audit shows greater accuracy than the previous TLD audit, justifying the reduction in audit tolerances. In the TLD audit, all outcomes were Pass (Optimal Level) suggesting that the tolerances were too conservative. In the OSLD audit 94% of the audits have resulted in Pass (Optimal level) and 6% of the audits have resulted in Pass (Action Level). All Pass (Action level) results have been resolved with a repeat OSLD audit, or an on-site ion chamber measurement.
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http://dx.doi.org/10.1118/1.4865786DOI Listing
March 2014

The Australian Clinical Dosimetry Service: a commentary on the first 18 months.

Australas Phys Eng Sci Med 2012 Dec 28;35(4):407-11. Epub 2012 Sep 28.

Australian Clinical Dosimetry Service, ARPANSA, Australia.

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http://dx.doi.org/10.1007/s13246-012-0161-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3562435PMC
December 2012

Provider volumes and early outcomes of primary total joint replacement in Ontario.

Can J Surg 2010 Jun;53(3):175-83

The Institute for Clinical Evaluative Sciences, Toronto, Ont., Canada.

Background: A relation between provider volume and outcome of total joint replacement (TJR) has not been demonstrated in Canada. Given the recent increase in TJR, changing patient characteristics and small sizes of previous Ontario studies, we reassessed whether adverse outcomes of TJR are related to hospital and surgeon procedure volumes.

Methods: We included all Ontarians aged 20 years and older who underwent a unilateral elective primary total hip replacement (THR) or total knee replacement (TKR) between April 2000 and March 2004. The main data sources were hospital discharge abstracts and physician billings. We defined provider volume as the average annual number of primary and revision procedures performed by hospitals and surgeons during the study period. We assessed the association between procedure volumes and acute length of hospital stay (ALOS) and between volume and rate of surgical complications during the index admission; death within 90 days of operation; readmission for amputation, fusion or excision within 1 year; and revision arthroplasty within 1 year. We adjusted for age, sex, comorbidity, arthritis type, teaching hospital status and discharge disposition. The analyses of hospital volume were adjusted for surgeon volume and vice versa.

Results: We included 20,290 patients who received THR and 27,217 who received TKR. Patient age, sex and comorbidity were significant predictors of complications and mortality. There were no associations between provider volume and mortality. Findings for other outcomes were mixed. Surgeon procedure volume was related to rates of revision THR but not to rates of revision TKR. Shorter ALOS was associated with male sex, younger age, fewer comorbidities, discharge to a rehabilitation unit or facility and greater surgeon volume.

Conclusion: Patient characteristics were significant predictors of complications, ALOS and mortality after primary TJR. Evidence for a relation between provider volume and outcome was limited and inconsistent.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2878994PMC
June 2010

High-resolution visualization of airspace structures in intact mice via synchrotron phase-contrast X-ray imaging (PCXI).

J Anat 2008 Aug;213(2):217-27

Department of Pulmonary Medicine, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia.

Anatomical visualization of airspace-containing organs in intact small animals has been limited by the resolution and contrast available from current imaging methods such as X-ray, micro-computed tomography and magnetic resonance imaging. Determining structural relationships and detailed anatomy has therefore relied on suitable fixation, sectioning and histological processing. More complex and informative analyses such as orthogonal views of an organ and three-dimensional structure visualizations have required different animals and image sets, laboriously processed to gather this complementary structural information. Precise three-dimensional anatomical views have always been difficult to achieve in small animals. Here we report the ability of phase-contrast synchrotron X-ray imaging to provide detailed two- and three-dimensional visualization of airspace organ structures in intact animals. Using sub-micrometre square pixel charge-coupled device array detectors, the structure and anatomy of hard and soft tissues, and of airspaces, is readily available using phase-contrast synchrotron X-ray imaging. Moreover, software-controlled volume-reconstructions of tomographic images not only provide unsurpassed image clarity and detail, but also selectable anatomical views that cannot be obtained with established histological techniques. The morphology and structure of nasal and lung airways and the middle ear are illustrated in intact mice, using two- and three-dimensional representations. The utility of phase-contrast synchrotron X-ray imaging for noninvasively localizing objects implanted within airspaces, and the detection of gas bubbles transiting live airways, are other novel features of this visualization methodology. The coupling of phase-contrast synchrotron X-ray imaging technology with software-based reconstruction techniques holds promise for novel and high-resolution non-invasive examination of airspace anatomy in small animal models.
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http://dx.doi.org/10.1111/j.1469-7580.2008.00950.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2526115PMC
August 2008

Imaging lung aeration and lung liquid clearance at birth.

FASEB J 2007 Oct 29;21(12):3329-37. Epub 2007 May 29.

Department of Physiology, Monash University, VIC 3800, Australia.

Aeration of the lung and the transition to air-breathing at birth is fundamental to mammalian life and initiates major changes in cardiopulmonary physiology. However, the dynamics of this process and the factors involved are largely unknown, because it has not been possible to observe or measure lung aeration on a breath-by-breath basis. We have used the high contrast and spatial resolution of phase contrast X-ray imaging to study lung aeration at birth in spontaneously breathing neonatal rabbits. As the liquid-filled fetal lungs provide little absorption or phase contrast, they are not visible and only become visible as they aerate, allowing a detailed examination of this process. Pups were imaged live from birth to determine the timing and spatial pattern of lung aeration, and relative levels of lung aeration were measured from the images using a power spectral analysis. We report the first detailed observations and measurements of lung aeration, demonstrating its dependence on inspiratory activity and body position; dependent regions aerated at much slower rates. The air/liquid interface moved toward the distal airways only during inspiration, with little proximal movement during expiration, indicating that trans-pulmonary pressures play an important role in airway liquid clearance at birth. Using these imaging techniques, the dynamics of lung aeration and the critical role it plays in regulating the physiological changes at birth can be fully explored.
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http://dx.doi.org/10.1096/fj.07-8208comDOI Listing
October 2007

Assessment of health-related quality of life in arthritis: conceptualization and development of five item banks using item response theory.

Health Qual Life Outcomes 2006 Jun 2;4:33. Epub 2006 Jun 2.

Department of Health Care and Epidemiology, University of British Columbia, Vancouver, BC, Canada.

Background: Modern psychometric methods based on item response theory (IRT) can be used to develop adaptive measures of health-related quality of life (HRQL). Adaptive assessment requires an item bank for each domain of HRQL. The purpose of this study was to develop item banks for five domains of HRQL relevant to arthritis.

Methods: About 1,400 items were drawn from published questionnaires or developed from focus groups and individual interviews and classified into 19 domains of HRQL. We selected the following 5 domains relevant to arthritis and related conditions: Daily Activities, Walking, Handling Objects, Pain or Discomfort, and Feelings. Based on conceptual criteria and pilot testing, 219 items were selected for further testing. A questionnaire was mailed to patients from two hospital-based clinics and a stratified random community sample. Dimensionality of the domains was assessed through factor analysis. Items were analyzed with the Generalized Partial Credit Model as implemented in Parscale. We used graphical methods and a chi-square test to assess item fit. Differential item functioning was investigated using logistic regression.

Results: Data were obtained from 888 individuals with arthritis. The five domains were sufficiently unidimensional for an IRT-based analysis. Thirty-one items were deleted due to lack of fit or differential item functioning. Daily Activities had the narrowest range for the item location parameter (-2.24 to 0.55) and Handling Objects had the widest range (-1.70 to 2.27). The mean (median) slope parameter for the items ranged from 1.15 (1.07) in Feelings to 1.73 (1.75) in Walking. The final item banks are comprised of 31-45 items each.

Conclusion: We have developed IRT-based item banks to measure HRQL in 5 domains relevant to arthritis. The items in the final item banks provide adequate psychometric information for a wide range of functional levels in each domain.
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http://dx.doi.org/10.1186/1477-7525-4-33DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1550394PMC
June 2006

Use of health care among adults with chronic and complex physical disabilities of childhood.

Disabil Rehabil 2005 Dec;27(23):1455-60

The Hospital for Sick Children, Toronto, Canada.

Purpose: The purpose of this study was to explore the patterns of health services utilization among adults with chronic and complex physical disabilities of childhood, specifically cerebral palsy, spina bifida, and acquired brain injuries.METHODS. A cohort of 345 young adults who had graduated from the Bloorview MacMillan Children's Centre was identified. Their health care records were extracted from Ontario Health Insurance Plan (OHIP) and Canadian Institute for Health Information (CIHI) databases, for a four-year period. These data were analysed to estimate the frequency of out-patient physician visits and admissions to hospital.RESULTS. The mean age of the sample was 21.9 years (range 19.0-26.9 years). The results show that 95% of the sample visited a physician at least once per year, and 24% had a primary care physician. On average, these adults visited physicians 11.5 times per year (approximately once per month) and were admitted to hospital once every 6.8 years.CONCLUSIONS. These results suggest that adults with complex physical disabling conditions from childhood have ongoing health issues that require frequent service. Their admission rate is 9.0 times that of the general population, and few have a primary care physician. A new model of service may be necessary for this high-needs group.
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http://dx.doi.org/10.1080/00222930500218946DOI Listing
December 2005

Comparison of methods to identify outliers observed in health services small area variation studies.

Stat Methods Med Res 2003 Dec;12(6):531-46

Population Health Sciences, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.

Small area variation analysis (SAV) is an established methodology in health services and epidemiological research. The goal is to demonstrate that rates differ across areas, and to explain these differences by differences in physician practice styles or patient characteristics. While the SAV statistics provide an overall variation estimate, they do not provide a statistical means to identify significant outliers. We compared the chi-square (chi2) test with three approaches in determining significant outliers in SAV. We used data from the Canadian Institute for Health Information (CIHI) for Ontario residents discharged between 1989 and 1991. Coronary artery bypass surgery, hysterectomy and hip replacement data were used to compare four statistics in determining outliers: the chi2 test, Swift's approximate bootstrap confidence interval (ABC), Carriere's T2 (T2) with simultaneous confidence intervals (SCI), and Gentleman's normalized scores (GNS). Both the ABC and SCI correct the skewness of the distribution of the adjusted rates. With large data, confidence intervals calculated by the normal or the ABC methods are indistinguishable. The T2 can be applied to also nonbinary events. For binary events, it is asymptotically the same as the chi2. The GNS ranks the rates, but the distribution of these ranks does not differ significantly from that of the adjusted rates. We concluded that when using large data with binary events, there is little advantage in using the ABC, SCI or GNS over the commonly known chi2. The chi2 remains a useful tool in small area variation analysis to 'screen' or flag potential differences beyond chance alone.
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http://dx.doi.org/10.1191/0962280203sm350oaDOI Listing
December 2003

Using publicly available directories to trace survey nonresponders and calculate adjusted response rates.

Am J Epidemiol 2003 Nov;158(10):1007-11

Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.

In population-based surveys, sample lists are often out of date by the time data collection begins. Consequently, response rates, and the perceived validity of the survey, may be compromised by the unknowing inclusion of ineligible subjects. A strategy to address this issue is ascertainment of survey nonrespondents' eligibility status, enabling post hoc adjustment of response rates. In 1995-1996, population surveys were carried out in two Ontario, Canada, communities. Despite intensive follow-up, the status of 8949 (18.6%) of the 48218 potential subjects in these surveys remained unknown. In response, 500 "unknowns" from each community were randomly selected for tracing by using publicly available telephone directories and, where applicable, city directories. These tracing efforts classified persons into one of three groups: "ineligible" (moved before the mailing), "true nonresponder" (present when the survey was mailed), and "remains unknown" (no directory listing found). Publicly available directories clarified the status of 76.0% of potential participants, reducing the proportion of "unknowns" from 18.6% to 4.6%. Applying the estimated proportions of "ineligibles" from each area resulted in response rates adjusted from 63.8% to 71.2% and from 72.8% to 74.9% in the survey areas. Publicly available directories were used to successfully trace the majority of survey nonresponders, thus strengthening confidence in the survey's results.
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http://dx.doi.org/10.1093/aje/kwg240DOI Listing
November 2003

Patient and provider factors related to comprehensive arthritis care in a community setting in Ontario, Canada.

J Rheumatol 2003 Aug;30(8):1846-50

Sunnybrook and Women's College Health Sciences Centre, Toronto, Ontario, Canada.

Objective: To determine factors that correlate with recommendations for nonpharmacologic and pharmacologic interventions (comprehensive therapy) in community dwelling adults.

Methods: Eligible participants were >/= 55 years of age with hip and knee arthritis symptoms and disability. Comprehensive therapy was classified as a recommendation for exercise and weight loss (if required) and any pharmacotherapy.

Results: Only one-half of participants received a recommendation for comprehensive therapy. Participants who had seen a specialist and a therapist were almost twice as likely to receive a recommendation for comprehensive therapy.

Conclusion: In our setting, many people with hip or knee arthritis were not receiving even minimum recommended treatment. Changes in educational and organizational policies are needed to address this situation.
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August 2003

A descriptive analysis of two mobile crisis programs for clients with severe mental illness.

Can J Public Health 2003 May-Jun;94(3):233-7

Department of Public Health Sciences, Faculty of Medicine, University of Toronto, Toronto, ON.

Purpose: To describe cases seen by two Mobile Crisis Programs (MCPs) for individuals with severe mental illnesses. Focus is on client characteristics, mental health status, interventions, referrals, and immediate outcomes.

Methods: Data were collected retrospectively through a chart review of clinical record forms and accompanying progress notes for cases seen by the MCPs over a one-year period. A total of 981 cases were included in the study. Data were analyzed using descriptive and bivariate statistics.

Results: Most cases involved clients who were female (60.2%), single (55.8%), living at home (56.8%), unemployed (85.6%), and between 20 and 44 years of age (44.5%). The two programs varied on a number of factors related to the demographic profile and mental health needs of the different geographical regions in which they are located.

Conclusions: Findings highlight the need for further research into how MCPs can be integrated with related mental health services in offering clients the least intrusive and most efficient services.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6980067PMC
December 2003

Do factors other than trauma volume affect attrition of ATLS-acquired skills?

J Trauma 2003 May;54(5):835-41

Department of Surgery, University of Toronto, National ATLS Faculty, American College of Surgeons, Ontario, Canada.

Background: We previously demonstrated that trauma patient volume affects attrition rate of Advanced Trauma Life Support (ATLS)-acquired skills. This study assesses the possible roles of age, gender, and practice specialty on attrition of these skills over 8 years.

Methods: Cognitive (assessed by the 40-item Multiple Choice Question Examination [MCQE]) and clinical (assessed by four trauma Objective Structured Clinical Examination [OSCE] stations) skills performance were compared among physicians who completed the ATLS course 0 months, 6 months, 2 years, 4 years, 6 years, and 8 years previously. The physicians were further divided into the following groups: age < 32 years (n = 72) or 32 years or older (n = 72), gender (41 women and 103 men), and specialty (54 surgeons, 90 nonsurgeons, and 22 general surgeons). Multivariate analysis of variance was used for statistical comparison over time and unpaired t tests for between-group comparisons for each time period, with p < 0.05 being considered statistically significant.

Results: Regarding age, MCQE decreased from 82.3 +/- 2.8% to 62.7 +/- 3.0% (mean +/- SD) for age < 32 and from 84.1 +/- 3.6% to 62.8 +/- 2.1% for age 32 or older (p = not significant). Overall OSCE score (maximum, 20) decreased similarly for age < 32 (18.0 +/- 0.4 to 13.6 +/- 2.0) and age > 32 or older (18.0 +/- 0.3 to 12.4 +/- 1.3). Decrease in Priorities and Organized Approach scores also showed no differences between the groups. Regarding gender, MCQE decreased similarly in both groups (women, 81.5 +/- 2.2% to 64.4 +/- 2.4%; men, 83.3 +/- 3.2% to 64.1 +/- 4.2%) and so did OSCE, Priorities, and Organized Approach scores. Regarding specialty, surgeons (83.0 +/- 3.1% to 66.1 +/- 4.5%), nonsurgeons (82.9 +/- 3.2% to 63.3 +/- 3.9%), and general surgeons (82.5 +/- 3.5% to 63.8 +/- 5.3%) showed similar decreases in MCQE scores. Overall OSCE scores and Priority and Approach scores decreased similarly in all specialty groups. When trauma volume was controlled, there was still no difference in attrition rate between surgeons and nonsurgeons.

Conclusion: Trauma patient volume is the most critical determinant of attrition rate of ATLS-acquired skills. Gender, age (at time of taking the course), and practice specialty do not alter this attrition rate.
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http://dx.doi.org/10.1097/01.TA.0000057233.97051.81DOI Listing
May 2003

The effect of education and income on need and willingness to undergo total joint arthroplasty.

Arthritis Rheum 2002 Dec;46(12):3331-9

Sunnybrook and Women's College Health Sciences Centre, Arthritis Community Research and Evaluation Unit, and Institute for Clinical Evaluative Sciences, University of Toronto, Toronto, Ontario, Canada.

Objective: Individuals with lower socioeconomic status (SES) receive less arthritis care, including joint arthroplasty. However, no studies have considered the expectations or needs of the patients. Our objective was to assess the effect of education and income on the potential need for, and the willingness to consider hip and knee arthroplasty.

Methods: Through a mail/telephone survey of 48,218 persons ages 55 years or older residing in 2 areas of Ontario, Canada, 3,307 individuals with moderate-to-severe hip/knee problems were identified. These individuals received a questionnaire to assess education, income, arthritis severity, and comorbidity. In a subset of these subjects, we conducted interviews to evaluate the willingness to consider arthroplasty, and we also performed clinical and radiographic examinations of the joints to validate self-reports of arthritis. The potential need for arthroplasty was defined as the presence of severe arthritis (as scored by the Western Ontario and McMaster Universities Osteoarthritis Index), with no absolute contraindications to surgery. Separate logistic regression models examined the independent effects of education and income on the potential need for, and definite willingness to consider arthroplasty, after controlling for age, sex, and region of residence. Potential unmet need was estimated as the proportion of subjects with the need for arthroplasty who were not already on a surgery waiting list, who were definitely willing to consider arthroplasty, and who had evidence of arthritis by examination and radiography.

Results: Response rates were at least 72% for all questionnaires and interviews. Less education (adjusted odds ratio [OR] 1.57 for less than high school versus postsecondary education, 95% confidence interval [95% CI] 1.17-2.11) and lower income (adjusted OR 1.83 for $40,000, 95% CI 1.24-2.70) were independently associated with a greater likelihood of having the potential need for arthroplasty. Among the subjects with potential need, neither education nor income was independently associated with a definite willingness to consider arthroplasty. Thus, taking willingness into consideration, individuals with less education and/or lower income were more likely to have potential unmet need for arthroplasty.

Conclusion: Persons with lower SES had a greater need for, and were equally willing to consider arthroplasty, compared with those with higher SES. Thus, observed SES disparities in the rates of performed arthroplasties cannot be explained by a lower need or less willingness to undergo arthroplasty in those with lower SES.
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http://dx.doi.org/10.1002/art.10682DOI Listing
December 2002

What influences family physicians' cancer screening decisions when practice guidelines are unclear or conflicting?

J Fam Pract 2002 Sep;51(9):760

Department of Family Medicine, East Tennessee State University, Box 70621, Johnson City, TN 37614, USA.

Objectives: To determine (a) the respondents' perceptions of 4 unclear or conflicting cancer screening guidelines: prostate-specific antigen (PSA) for men over 50, mammography for women 40-49, colorectal screening by fecal occult blood testing (FOBT), and colonoscopy for patients over 40; and (b) the influence of various factors on the decision to order these tests.

Study Design: National Canadian mail survey of randomly selected family physicians.

Population: Family physicians in active practice (n=565) selected from rural and urban family medicine sites in 5 provinces representing the main regions in Canada.

Outcome Measured: Agreement with guideline statements, and decision to order screening test in 6 clinical vignettes.

Results: Of 565 surveys mailed, 351 (62.1%) were returned. Most respondents agreed with the Canadian Task Force recommendations, and most believed that various guidelines for 3 of the 4 screens were conflicting (PSA 86.6%; mammography 67.5%; FOBT 62.4%). Patient anxiety about cancer, patient expectations of being tested, and a positive family history of cancer increased the odds that the 4 tests would be ordered. A good quality patient-MD relationship decreased the odds of ordering a mammogram. Screening decisions were also significantly influenced by the respondents' beliefs about whether screening was recommended and whether screening could cause more harm than good. A physician's sensitivity to his or her colleagues' practice influenced screening decisions regarding PSA and mammography.

Conclusions: These results suggest a conceptual framework for understanding the determinants of screening behavior when guidelines are unclear or conflicting.
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September 2002

Adverse effects of observational studies when examining adverse outcomes of drugs: case-control studies with low prevalence of exposure.

Drug Saf 2002 ;25(9):677-87

Institute for Clinical Evaluative Sciences, North York, Ontario, Canada.

Objectives: The case-control study is commonly used to examine adverse drug events, in which prevalence of exposure in the source population is frequently very low. The objective of the current study was to examine the bias inherent in the odds ratio assessing the association between exposure and an adverse outcome when prevalence of exposure in the source population is extremely low.

Design: Monte Carlo simulations examined the effect of sample size, exposure prevalence, and magnitude of the underlying odds ratio on the bias of the estimated risk ratio, and the power to detect a non-zero risk ratio.

Results: Once the underlying odds ratio was at least four, the adverse effects of low prevalence of exposure was minimal. Studies with small sample sizes and low prevalence of exposure, coupled with small to moderate effect sizes, can result in biased estimates of association between exposure and disease status. With a sample size of 200 and an exposure prevalence of 0.5% in the control population, the bias in the estimated odds ratio can be as large as 115%. However, bias becomes negligible as sample size becomes large (n > or = 2000), even when prevalence of exposure is very low. Once the expected number of exposed controls is at least eight, the bias in the estimated odds ratio was no more than 5%.

Conclusions: Studies with small sample sizes and low prevalence of exposure, coupled with small to moderate effect sizes can result in biased estimates of association between exposure status and adverse drug effects. However, bias becomes negligible as sample size becomes large.
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http://dx.doi.org/10.2165/00002018-200225090-00006DOI Listing
September 2002

Adverse effects of observational studies when examining adverse outcomes of drugs: case-control studies with low prevalence of exposure.

Drug Saf 2002 ;25(9):677-87

Institute for Clinical Evaluative Sciences, North York, Ontario, Canada.

Objectives: The case-control study is commonly used to examine adverse drug events, in which prevalence of exposure in the source population is frequently very low. The objective of the current study was to examine the bias inherent in the odds ratio assessing the association between exposure and an adverse outcome when prevalence of exposure in the source population is extremely low.

Design: Monte Carlo simulations examined the effect of sample size, exposure prevalence, and magnitude of the underlying odds ratio on the bias of the estimated risk ratio, and the power to detect a non-zero risk ratio.

Results: Once the underlying odds ratio was at least four, the adverse effects of low prevalence of exposure was minimal. Studies with small sample sizes and low prevalence of exposure, coupled with small to moderate effect sizes, can result in biased estimates of association between exposure and disease status. With a sample size of 200 and an exposure prevalence of 0.5% in the control population, the bias in the estimated odds ratio can be as large as 115%. However, bias becomes negligible as sample size becomes large (n > or = 2000), even when prevalence of exposure is very low. Once the expected number of exposed controls is at least eight, the bias in the estimated odds ratio was no more than 5%.

Conclusions: Studies with small sample sizes and low prevalence of exposure, coupled with small to moderate effect sizes can result in biased estimates of association between exposure status and adverse drug effects. However, bias becomes negligible as sample size becomes large.
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http://dx.doi.org/10.2165/00002018-200225090-00006DOI Listing
September 2002

Gender and outpatient mental health service use.

Soc Sci Med 2002 Jan;54(1):1-10

Department of Psychiatry, University of Toronto, Canada.

The purpose of this study is to describe gender differences in the use of outpatient mental health services and to identify potential determinants of this use. The study sample, N = 7475 respondents 18-64 years, was drawn from the Mental Health Supplement to the Ontario Health Survey. For theoretical and empirical reasons, type of mental disorder was defined as: a Mood and/or Anxiety Disorder (Mood/Anx) or a Substance Use Disorder and/or Antisocial Behaviours (Subs/Asb) within the past year. Use was defined in relation to providers seen within the past year. Descriptive and multiple logistic regression analyses were employed including type of mental disorder, social and economic factors. Female gender remained positively associated with any use despite adjustments (adjusted OR: 1.7; 95% CI: 1.2: 2.4). The magnitude of this association was consistent across the levels of the study variables and various measures of use except volume of use where there were no gender differences. Mood/Anx appeared to mediate the gender-use relationship and was strongly associated with use (adjusted OR: 8.4; 95% CI: 5.9; 11.9). Subs/Asb was also related to use (adjusted OR: 2.6; 95% CI: 1.5; 4.3) but not to the same degree as Mood/Anx. Mood/Anx explained 60% of the crude Subs/Asb-use relationship. The evidence to suggest that Subs/Asb mediated the gender-use relationship was mixed. These findings raise questions about gender differences in illness and reporting behaviours and the health care system in its preferential treatment of women and those with Mood/Anx.
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http://dx.doi.org/10.1016/s0277-9536(01)00002-8DOI Listing
January 2002

Can the health utilities index measure change?

Med Care 2001 Jun;39(6):562-74

Department of Health Care and Epidemiology, University of British Columbia, Canada and the Arthritis Research Centre of Canada, Vancouver, Canada.

Background: The Health Utilities Index (HUI) is a multidimensional, preference-weighted measure of health status. It comprises eight health attributes, aggregated into a single utility score.

Objectives: The purpose of the study was to investigate the ability of the HUI to detect changes in health status in a general population cohort.

Research Design: Health status changes were analyzed in the full cohort and in persons who were diagnosed with chronic conditions, hospitalized, or became restricted in daily activities.

Subjects: To assess responsiveness, longitudinal data was used from the National Population Health Survey conducted in Canada in 1994 - 1995 and 1996 - 1997. We used cross-sectional data from the 1996 sample to classify chronic conditions into mild, moderate, and severe.

Measures: Two measures of responsiveness were calculated: Standardized Response Mean (SRM) and Sensitivity Coefficient (SC). The HUI was compared with a global health index-the Self-Rated Health (SRH) scale.

Results: HUI scores improved between the two NPHS cycles in all age-sex groups, except men 65 years of age and older. Among the respondents who remained free of chronic conditions, improvements were seen primarily in the cognitive and emotional domains. The HUI deteriorated among persons who were diagnosed between the two cycles with a severe chronic condition, were hospitalized, or became restricted in activity, but not in those diagnosed with a moderate condition. The SRMs were generally smaller for the HUI compared with the SRH.

Conclusions: The HUI responds to changes in health status associated with serious chronic illnesses. However, changes in the HUI do not always coincide with changes in self-reported health. Properties of the HUI scales require further study.
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http://dx.doi.org/10.1097/00005650-200106000-00005DOI Listing
June 2001
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