The use of Rasch measurement to improve the Oswestry classification scheme

Understanding how individualised physiotherapy or advice altered different elements of disability for people with low back pain using network analysis

PURPOSE

The Oswestry Disability Index (ODI) is a common aggregate measure of disability for people with Low Back Pain (LBP). Scores on individual items and the relationship between items of the ODI may help understand the complexity of low back disorders and their response to treatment. In this study, we present a network analysis to explore how individualised physiotherapy or advice might influence individual items of the ODI, and the relationship between those items, at different time points for people with LBP.

METHODS

Data from a randomised controlled trial (n = 300) comparing individualised physiotherapy versus advice for low back pain were used. A network analysis was performed at baseline, 5, 10, 26 and 52 weeks, with the 10 items of the Oswestry Disability Index modelled as continuous variables and treatment group (Individualised Physiotherapy or Advice) modelled as a dichotomous variable. A Mixed Graphical Model was used to estimate associations between variables in the network, while centrality indices (Strength, Closeness and Betweenness) were calculated to determine the importance of each variable.

RESULTS

Individualised Physiotherapy was directly related to lower Sleep and Pain scores at all follow-up time points relative to advice, as well as a lower Standing score at 10-weeks, and higher Lifting and Travelling scores at 5-weeks. The strongest associations in the network were between Sitting and Travelling at weeks 5 and 26, between Walking and Standing at week 10, and between Sitting and Standing scores at week 52. ODI items with the highest centrality measures were consistently found to be Pain, Work and Social Life.

CONCLUSION

This study represents the first to understand how individualised physiotherapy or advice differentially altered disability in people with LBP. Individualised Physiotherapy directly reduced Pain and Sleep more effectively than advice, which in turn may have facilitated improvements in other disability items. Through their high centrality measures, Pain may be considered as a candidate therapeutic target for optimising LBP management, while Work and Socialising may need to be addressed via intermediary improvements in lifting, standing, walking, travelling or sleep. Slower (5-week follow-up) improvements in Lifting and Travelling as an intended element of the Individualised Physiotherapy approach did not negatively impact any longer-term outcomes.

TRIALS REGISTRATION

ACTRN12609000834257.

Validation of the Fullerton Advanced Balance Scale in children with cerebral palsy

Background/Aims:

Cerebral palsy is classified by the type of motor impairment. The ability to balance differs depending on the level of disability. The aim of this research was to investigate the item fit and item difficulty of the Fullerton Advanced Balance Scale in children with cerebral palsy, and to compare item fit and difficulty in individuals with diplegia and hemiplegia.

Methods:

Forty children with cerebral palsy completed the 10-item Fullerton Advanced Balance Scale questionnaire. Rasch analysis was used to identify the psychometric properties of the Fullerton Advanced Balance Scale and compare item fit and difficulty in two groups: children with diplegia and children with hemiplegia.

Findings:

Item 2 showed misfit statistics for all participants. Items 1 and 2 showed misfit statistics in hemiplegia, whereas no items showed misfit in diplegia.

Conclusions:

Item fit and difficulty need to be considered in relation to the level of disability when evaluating balance in children with cerebral palsy.

Analysis and comparison of the psychometric properties of two balance scales for elderly adults

Background/Aims:

The aim of this research was to verify psychometric properties of the Berg Balance Scale and the Fullerton Advanced Balance Scale, and compare the item difficulty between the two scales.

Methods:

A total of 97 community-dwelling older adults participated in this study. All participants were assessed on their degree of balance ability by the Berg Balance Scale and the Fullerton Advanced Balance Scale, respectively. We identified the psychometric properties and compared the item difficulty of the two scales using the Rasch analysis.

Findings:

Among the items on the Berg Balance Scale, the Standing to sitting and Transfers items showed misfit statistics. The most difficult item was Standing on one foot, whereas the easiest item was Sitting unsupported. In the case of the Fullerton Advanced Balance Scale, the Standing with feet together and eyes closed, Stand on foam, eyes closed and Walk with head turns items showed misfit statistics. Also, the most difficult item was Stand on one leg (logit value, 2.93), whereas the easiest item was Turn in full circle. Among the 24 items of the combined Berg Balance Scale and Fullerton Advanced Balance Scale, 13 items (nine items for the Fullerton Advanced Balance Scale and four items on the Berg Balance Scale) had positive logit values, and 11 items (one item on the FAB and 10 on the Berg Balance Scale) had negative logit values.

Conclusions:

Both the Berg Balance Scale and the Fullerton Advanced Balance appear to be reliable and valid tools to assess balance function in older adults. However, the Berg Balance Scale is suitable for assessing balance ability in a group of lower functioning older adults, whereas, the Fullerton Advanced Balance is suitable for assessing balance ability in a group of higher functioning older adults.

A systematic review highlights the need to investigate the content validity of patient-reported outcome measures for physical functioning in patients with low back pain

OBJECTIVES

To summarize the evidence on content and structural validity of 17 patient-reported outcome measures (PROMs) to measure physical functioning in patients with low back pain (LBP).

STUDY DESIGN AND SETTING

MEDLINE, EMBASE, CINAHL, PsycINFO, SportDiscus, and Google Scholar were searched (February 2017). Records on development and studies assessing content validity or unidimensionality in patients with LBP were included. Two reviewers defined eligible studies and assessed their methodological quality with updated Consensus-based Standards for the Selection of Health Measurement Instruments standards. Evidence was synthesized for three separate aspects of content validity: relevance, comprehensiveness, and comprehensibility, and for unidimensionality, a modified GRADE approach was applied to evidence synthesis.

RESULTS

High-quality evidence showed that 24-item Roland Morris Disability Questionnaire (RMDQ-24) is a comprehensible but not comprehensive PROM. Low to very low quality evidence underpinned the content validity of the other PROMs. Unidimensionality was: sufficient for Brief Pain Inventory pain interference subscale (moderate quality evidence); inconsistent for RMDQ-23, Oswestry Disability Index 2.1a (ODI 2.1a), and Quebec Back Pain Disability Scale (moderate quality); insufficient for RMDQ-24, ODI 1.0, and RMDQ-18 (high quality) and Short Form 36 physical functioning subscale (SF36-PF, moderate quality).

CONCLUSION

The content validity of PROMs to measure physical functioning in patients with LBP is understudied. Structural validity of several widely used PROMs is problematic.

Construct validity of the Eating Assessment Tool (EAT-10)

PURPOSE

We aimed to evaluate the construct validity of the Eating Assessment Tool (EAT-10) by determining its dimensionality, rating scale integrity, item-person match, precision and relationship with the degree of airway invasion and functional oral intake.

METHODS

We conducted a retrospective analysis of patients' EAT-10 scores. We used the Rasch rating scale model. We investigated correlations between the EAT-10 and scores on the Penetration-Aspiration Scale (PAS) and Functional Oral Intake Scale (FOIS).

RESULTS

The median score of the EAT-10 from 127 patients was 16 of 40 (range 0-40). Confirmatory factor analysis supported unidimensionality. The 5-point rating scale categories met published criteria. Two items misfit the Rasch model and two other items displayed differential item functioning. Rasch person reliability was 0.79. Our patient cohort was divided into three person-strata. Correlations between the EAT-10 and the PAS and FOIS were weak to moderate in strength (respectively: r = 0.26, p = 0.0036; r = -0.27, p = 0.0027).

CONCLUSIONS

Our analyses identified deficits in the construct validity of the EAT-10 suggestive of a need to improve the EAT-10 to support its frequent use in clinical practice and research. Implications for Rehabilitation Swallowing disorders are associated with severe complications, such as pneumonia and malnutrition, and impose both social and psychological burdens on patients. The Eating Assessment Tool is a self-report instrument developed to estimate initial dysphagia severity and monitor change in patient-reported dysphagia symptoms as a response to treatment. This study shows that the Eating Assessment Tool has deficits in its construct validity and a need to improve the instrument to support its frequent use in clinical practice and research.

Oswestry Disability Index: a psychometric analysis with 1,610 patients

BACKGROUND

One-fourth of the adult US population has or will experience back pain and has undergone one of a myriad of treatments. Understanding the outcomes of these many treatments from pharmacologic to surgical, from manipulation to modality, allows for a better understanding and value-driven decision making. Patient-reported outcome measures are the current standard and include general and disease-specific measures. The Oswestry Disability Index (ODI) is the most commonly used disease-specific patient-reported outcome tool to measure functional disability related to back pain. Few studies have evaluated its psychometric properties in a large patient sample using a modern tool such as the Rasch analysis model. This study aims to identify the benefits and deficiencies of the ODI as an outcome tool for assessing patients with back pain.

PURPOSE

This study aimed to investigate the psychometric properties, performance, and applicability of the ODI in patients with back pain who visited a university-based outpatient clinic.

STUDY DESIGN

This study used a secondary analysis-assessment of diagnostic tool on consecutive patients.

PATIENT SAMPLE

The sample comprised 1,610 patients visiting an academic spine center.

OUTCOME MEASURES

The ODI was the outcome measure.

METHODS

Detailed Rasch analysis of the ODI was performed. Standard descriptive statistics were also assessed.

RESULTS

The ODI performed well overall. It demonstrated suboptimal unidimensionality (ie, unexplained variance after accounting for the first dimension) of 8.3%. Person reliability was good, at 0.85, and item reliability was excellent, at 1.00. The overall item fit for the ODI was good with an outfit mean square of 1.02. The ODI had a floor effect of 29.9% and ceiling effect of 3.9%. The raw score to measure correlation of the ODI was excellent, at 0.944.

CONCLUSIONS

The ODI performed relatively well overall, with some problematic findings. It had good person and item reliability, although it did not demonstrate strong evidence of unidimensionality. The ODI has moderately poor coverage, with a very large floor effect and small ceiling effect, which could present a challenge in interpreting results of scores at the end of the spectrum.

Measurement precision of the disability for back pain scale-by applying Rasch analysis

Background

The Oswestry Disability Index (ODI) is widely used for patients with back pain. However, few studies have examined its psychometric properties using modern measurement theory. The purpose of this study was to investigate the psychometric properties of the ODI in patients with back pain using Rasch analysis.

Methods

A total of 408 patients with back pain participated in this cross-sectional study. Patients were recruited from the orthopedic, neurosurgery, rehabilitation departments and pain clinic of two hospitals. Rasch analysis was used to examine the Chinese version of ODI 2.1 for unidimensionality, item difficulty, category function, differential item functioning, and test information.

Results

The fit statistics showed 10 items of the ODI fitted the model’s expectation as a unidimensional scale. The ODI measured the different levels of functional limitation without skewing toward the lower or higher levels of disability. No significant ceiling and floor effects and gaps among the items were found. The reliability was high and the test information curve demonstrated precise dysfunction estimation.

Conclusions

Our results showed that the ODI is a unidimensional questionnaire with high reliability. The ODI can precisely estimate the level of dysfunction, and the item difficulty of the ODI matches the person ability. For clinical application, using logits scores could precisely represent the disability level, and using the item difficulty could help clinicians design progressive programs for patients with back pain.

Lumbar computerized adaptive test and Modified Oswestry Low Back Pain Disability Questionnaire: relative validity and important change

STUDY DESIGN

Retrospective analysis of longitudinal, observational cohort data.

OBJECTIVES

To compare discriminating ability and minimal clinically important improvement (MCII) calculated using functional status (FS) measures estimated from the lumbar computerized adaptive test (LCAT) and Modified Oswestry Low Back Pain Disability Questionnaire (ODQ).

BACKGROUND

The LCAT and ODQ are commonly used to estimate FS in patients seeking outpatient therapy but have not been compared directly.

METHODS

Data from 8198 adult patients who completed the LCAT and ODQ at intake were analyzed, 3379 (41%) of whom completed both surveys at discharge. Global ratings of change data were available for 980 patients. Discriminating ability of FS estimates from the LCAT and ODQ was estimated using relative validity, calculated by dividing F values from LCAT and ODQ analyses of covariance for important risk-adjustment variables. MCII was estimated using receiver-operating-characteristic analyses by quartiles of intake FS values, and areas under the curves were compared.

RESULTS

Relative validity ratios favored the LCAT for age (3.7; 95% confidence interval [CI]: 2.0, 8.9), acuity (1.3; 95% CI: 1.1, 1.6), comorbidities (1.8; 95% CI: 1.3, 2.6), and surgical history (1.8; 95% CI: 1.2, 2.9). MCII cut scores per quartile favored the LCAT. Receiver-operating-characteristic areas under the curves were not different.

CONCLUSION

FS measures estimated by both questionnaires had similar psychometric characteristics. The LCAT FS estimates tended to be more discriminating than ODQ FS estimates. MCII cut scores by quartile of intake FS favored the LCAT. Given the need to be efficient and precise in estimating measures of FS, particularly in older patients, results favor the LCAT in busy, automated outpatient therapy clinics, which are increasingly serving an aging population.

Measure of experimental pain using Rasch analysis

Most common instruments used to assess the painfulness of nociceptive stimuli and the perception of such stimuli are ordinal. This property limits arithmetical operations and statistical procedures that can be applied on their numbers. The Rasch methodology provides mathematical procedures for transforming scores on an ordinal scale into measures on an interval scale. The present paper aims at presenting the basics of this methodology by applying it to the measurement of experimentally induced pain. Six blocks of seven CO(2) laser heat stimuli varying in intensity were delivered on the hand of 100 healthy subjects. They rated their pain perception on a three-level verbal rating scale (not painful, slightly painful, painful). One member of the family of Rasch models, the many-facet model, was applied to the analysis of these ratings. The analysis provided linear measures of the painfulness for each intensity of stimulation, of the pain perception of each subject and of the painfulness of each successive block. All these measures are located on a single pain perception continuum. Advantages and disadvantages of this methodology will be discussed in terms of subsequent possible mathematical analyses, statistical tests and implications for experimental and clinical investigations.

The clinical value of a cluster of patient history and observational findings as a diagnostic support tool for lumbar spine stenosis

OBJECTIVE

The study aims to create a diagnostic support tool to indicate the likelihood of the presence of lumbar spinal stenosis (LSS) using a cluster of elements from the patient history and observational findings.

DESIGN

The study is case based and case controlled.

SETTING

The study was performed in the tertiary care of a medical center.

SUBJECTS

There were a total of 1,448 patients who presented with a primary complaint of back pain with or without leg pain.

METHODS

All patients underwent a standardized clinical examination. The diagnosis of LSS was made by one of two experienced orthopaedic surgeons based on clinical findings and imaging. Data from the patient history and observational findings were then statistically analysed using bivariate analysis and contingency tables.

RESULTS

The most diagnostic combination included a cluster of: 1) bilateral symptoms; 2) leg pain more than back pain; 3) pain during walking/standing; 4) pain relief upon sitting; and 5) age>48 years. Failure to meet the condition of any one of five positive examination findings demonstrated a high sensitivity of 0.96 (95% CI=0.94-0.97) and a low negative likelihood ratio (LR-) of 0.19 (95% CI=0.12-0.29). Meeting the condition of four of five examination findings yielded a LR+ of 4.6 (95% CI=2.4-8.9) and a post-test probability of 76%.

CONCLUSION

The high sensitivity of the diagnostic support tool provides the potential to reduce the incidence of unnecessary imaging when the diagnosis of LSS is statistically unlikely. In patients where the condition of four of the five findings was present, the post-test probability of 76% suggests that imaging and further workup are indicated. This is an inexpensive but powerful tool, with a potential to increase diagnostic efficiency and reduce cost by narrowing the indications for imaging.

The first stage of developing preference-based measures: constructing a health-state classification using Rasch analysis

OBJECTIVE

To set out the methodological process for using Rasch analysis alongside classical psychometric methods in the development of a health-state classification that is amenable to valuation.

METHODS

The overactive bladder questionnaire is used to illustrate a five step process for deriving a reduced health-state classification from an existing non-preference-based health-related quality-of-life instrument. Step I uses factor analysis to establish instrument dimensions, step II excludes items that do not meet the initial validation process and step III uses criteria based on Rasch analysis and other psychometric testing to select the final items for the health-state classification. In step IV, item levels are examined and Rasch analysis is used to explore the possibility of reducing the number of item levels. Step V repeats steps I-IV on alternative data sets in order to validate the selection of items for the health-state classification.

RESULTS

The techniques described enable the construction of a five-dimension health-state classification, the OAB-5D, amenable to valuation tasks that will allow the derivation of preference weights.

CONCLUSIONS

The health-related quality of life of patients with conditions like overactive bladder can be valued and quality adjustment weights estimated for calculation of quality-adjusted life years.

A method to provide a more efficient and reliable measure of self-report physical work capacity for patients with spinal pain

Self-report measures of functional ability are commonly used in occupational rehabilitation to measure the current status of an individual and his or her progress in response to intervention. Most of these measures have been developed using classical test theory that does not provide calibration of the items. Methods of test development that originated in the field of Education have been applied recently to healthcare measures, providing item calibration and allowing proportional evaluation of total scores. The purpose of this article is to demonstrate the application of these methods in the revision of an existing self-report measure. The potential value of these methods to improve established measures is demonstrated.

Rasch analysis of three versions of the Oswestry Disability Questionnaire

The purpose of the study was to explore the construct validity of three versions of the Oswestry Disability Questionnaire for low back pain using Rasch analysis. The three versions of the ODQ share 9 items and differ on one other. About 100 patients with non-specific low back pain seeking physiotherapy treatment at hospital outpatient departments and physiotherapy private practices completed the 12 Oswestry items as part of a battery of questionnaires. Rasch analysis revealed that four items (Personal Care, Standing, Sex Life and Social Life) had disordered response thresholds and one item (Walking) showed differential item functioning by age. The 10 standard Oswestry items and a modified version in which Sex Life is replaced by Work/Housework showed adequate overall fit to the Rasch model (chi(2)P>.01). The third version, in which Sex Life is replaced by Changing Degree of Pain, did not fit the model (chi(2)P=.006) and the Changing Degree of Pain item was misfitting (residual 2.34, P=.007). These findings suggest that either of the first two of the three versions of this widely used low back pain outcome measure should be selected over the third. Users should also be aware that for some items the rating scale steps do not perform as intended.

Simulated computerized adaptive test for patients with lumbar spine impairments was efficient and produced valid measures of function

OBJECTIVE

To equate physical functioning (PF) items with Back Pain Functional Scale (BPFS) items, develop a computerized adaptive test (CAT) designed to assess lumbar spine functional status (LFS) in people with lumbar spine impairments, and compare discriminant validity of LFS measures (theta(IRT)) generated using all items analyzed with a rating scale Item Response Theory model (RSM) and measures generated using the simulated CAT (theta(CAT)).

METHODS

We performed a secondary analysis of retrospective intake rehabilitation data.

RESULTS

Unidimensionality and local independence of 25 BPFS and PF items were supported. Differential item functioning was negligible for levels of symptom acuity, gender, age, and surgical history. The RSM fit the data well. A lumbar spine specific CAT was developed that was 72% more efficient than using all 25 items to estimate LFS measures. theta(IRT) and theta(CAT) measures did not discriminate patients by symptom acuity, age, or gender, but discriminated patients by surgical history in similar clinically logical ways. theta(CAT) measures were as precise as theta(IRT) measures.

CONCLUSION

A body part specific simulated CAT developed from an LFS item bank was efficient and produced precise measures of LFS without eroding discriminant validity.

Dimensionality, Internal Consistency, and Item Analysis of the National Health and Nutrition Examination Surveys Activities of Daily Living Instrument Among Patients With Report of Low Back Pain

OBJECTIVE

To measure selected psychometric properties of individual item responses from the National Health and Nutrition Examination Surveys (NHANES) activities of daily living (ADL) instrument among a population of patients with low back pain (LBP).

METHODS

The study group consisted of 926 individual attendees of a traditional medical appointment. All subjects had self-reported LBP and completed questions within the NHANES ADL instrument, a 16-item questionnaire designed to represent the internal latent construct of ADL. Data analyses included exploratory factor analysis, internal consistency measures, and polytomous (graded) item response theory.

RESULTS

The NHANES ADL instrument is a unidimensional and internally consistent measure of ADL. Graded item response theory analyses indicated that although some variability exists, all 16 single items were sensitive measures of the latent construct of ADL. Most item responses demonstrated high discrimination.

CONCLUSION

Individual use of selected items of the NHANES ADL instrument may further improve the capacity of the health care provider in measuring and recording dysfunction associated with LBP.

Measurement qualities of a self-report and therapist-scored functional capacity instrument based on the Dictionary of Occupational Titles

Studies provide convincing arguments to support the development of functional capacity instruments based on the Dictionary of Occupational Titles (DOT). The purpose of this study is to investigate the item-level measurement qualities of a newly developed DOT-based functional capacity instrument for clients undergoing rehabilitation treatment for back pain. Client and therapist ratings were collected on 124 clients from 27 rehabilitation sites using the newly developed Occupational Rehabilitation Data Base (ORDB) functional capacity instrument. Rasch analysis was used to investigate: (1) unidimensionality, (2) hierarchical item difficulty continuum, (3) rater severity, and 4) person-item match. Overall, the functional capacity scale of the ORDB showed good measurement qualities. All items, except the Handling item fit the Rasch measurement model. Because of high fit statistics and loading on factors independent from the remainder of the items, the "handling" item was removed, from further analyses. Separate client-rated and therapist-rated instruments retained good item-level psychometrics. While client and therapist items showed similar item-difficulty hierarchical structures, clients had a tendency to be more severe in their rating and the correlation between client and therapist ratings was relatively low, 0.32. These findings suggest that Handling items should not be included as a DOT measure for clients with back pain. While the above psychometric study supports using client or therapist ratings as independent instruments, the lack of concordance between these ratings requires further investigation.

A Quality of Life Comparison of People Wearing Spectacles or Contact Lenses or Having Undergone Refractive Surgery

PURPOSE

To demonstrate the use of the Quality of Life Impact of Refractive Correction (QIRC) questionnaire for comparing the quality of life of pre-presbyopic individuals with refractive correction by spectacles, contact lenses, or refractive surgery.

METHODS

The 20-item QIRC questionnaire was administered to 104 spectacle wearers, 104 contact lens wearers, and 104 individuals who had undergone refractive surgery (N = 312). These groups were similar for gender, ethnicity, socioeconomic status, and refractive error. The main outcome measure was QIRC overall score (scaled from 0 to 100), a measure of refractive correction related quality of life. Groups were compared for overall QIRC score and on each question by analysis of variance, adjusted for age, with post hoc significance testing (Sheffé).

RESULTS

On average, refractive surgery patients scored significantly better (mean QIRC score 50.2 +/- 6.3, F(2,309) = 15.18, P < .001) than contact lens wearers (46.7 +/- 5.5, post hoc P < .001) who were in turn significantly better than spectacle wearers (44.1 +/- 5.9, post hoc P < .01). Convenience questions chiefly drove the differences between groups, although functioning, symptoms, economic concerns, heath concerns, and well being were also important. Spectacle wearers with low strength prescriptions (46.18 +/- 5.05) scored significantly better than those with medium strength prescriptions (42.74 +/- 6.08, F(2,190) = 3.66, P < .05, post hoc P < .05). A small number (n = 7, 6.7%) of refractive surgery patients experienced postoperative complications, which impacted quality of life (37.86 +/- 2.13).

CONCLUSIONS

Quality of life was lowest in spectacle wearers, particularly those with higher corrections. Contact lens wearers had significantly better QIRC score than spectacle wearers. Refractive surgery patients scored significantly better than both. However, this was accompanied by a small risk of poor quality of life due to postoperative complications. The QIRC is an effective outcome measure for quality of life impact of refractive correction.

Changes in quality of life after laser in situ keratomileusis for myopia

PURPOSE

To measure quality of life (QoL) outcome in prepresbyopic myopic patients having laser in situ keratomileusis (LASIK) refractive surgery using the Quality of Life Impact of Refractive Correction (QIRC) questionnaire and to compare the QoL of preoperative patients with a sample of spectacle and contact lens wearers not considering refractive surgery.

SETTING

Department of Optometry, University of Bradford, Bradford, and Ultralase, Leeds, West Yorkshire, United Kingdom.

METHODS

The validated QIRC questionnaire was prospectively completed by 66 patients before and 3 months after LASIK. Patients had myopia greater than 0.50 diopters (D) (range --0.75 to --10.50 D) and were aged 16 to 39 years. Patients were also directly asked to evaluate their QoL after surgery.

RESULTS

Overall QIRC scores improved after LASIK from a mean of 40.07+/- 4.30 (SD) to 53.09+/- 5.25 (F(1,130)=172.65, P<.001). Greater improvements occurred in women (53.83+/- 5.46) than in men (49.39+/- 5.94; F(1,64)=9.37, P<.005). Overall, 15 of the 20 questions (especially convenience, health concerns, and well-being questions) showed significantly improved scores (P<.05). Patients who "strongly agreed" (53.96+/- 4.91, n=33) or "agreed" (51.78+/- 6.19, n=23) had improved QoL and had significantly higher QIRC scores than those who "neither agreed nor disagreed" (44.36+/- 4.97, n=5) or "strongly disagreed" (42.82, n=1) (F(1,60)=11.24, P<.001). The matched group not contemplating LASIK scored 42.41 +/- 3.89 on QIRC overall.

CONCLUSIONS

Large improvements in QIRC QoL scores were found after LASIK for myopia in the majority of patients, with greater improvements in women. A small number of patients (4.5%) had decreased QIRC QoL scores, and these were associated with complications. People presenting for LASIK scored measurably poorer than matched patients not contemplating refractive surgery.

Simulated computerized adaptive tests for measuring functional status were efficient with good discriminant validity in patients with hip, knee, or foot/ankle impairments

BACKGROUND AND OBJECTIVE

To develop computerized adaptive tests (CATs) designed to assess lower extremity functional status (FS) in people with lower extremity impairments using items from the Lower Extremity Functional Scale and compare discriminant validity of FS measures generated using all items analyzed with a rating scale Item Response Theory model (theta(IRT)) and measures generated using the simulated CATs (theta(CAT)).

METHODS

Secondary analysis of retrospective intake rehabilitation data.

RESULTS

Unidimensionality of items was strong, and local independence of items was adequate. Differential item functioning (DIF) affected item calibration related to body part, that is, hip, knee, or foot/ankle, but DIF did not affect item calibration for symptom acuity, gender, age, or surgical history. Therefore, patients were separated into three body part specific groups. The rating scale model fit all three data sets well. Three body part specific CATs were developed: each was 70% more efficient than using all LEFS items to estimate FS measures. theta(IRT) and theta(CAT) measures discriminated patients by symptom acuity, age, and surgical history in similar ways. theta(CAT) measures were as precise as theta(IRT) measures.

CONCLUSION

Body part-specific simulated CATs were efficient and produced precise measures of FS with good discriminant validity.

The Quality of Life Impact of Refractive Correction (QIRC) Questionnaire: Development and Validation

BACKGROUND

The purpose of the study was to develop a questionnaire that could quantify the quality of life (QOL) of people with refractive correction by spectacles, contact lenses, and refractive surgery in the prepresbyopic age group.

METHODS

The questionnaire was developed and validated using traditional methods and Rasch analysis. A 90-item pilot questionnaire was developed through extensive literature search and use of professional and lay focus groups. Pilot study data were obtained from 306 subjects for item reduction to produce the 20-item Quality of Life Impact of Refractive Correction (QIRC) questionnaire. Validity and reliability studies (test-retest reliability with intraclass correlation coefficient and Bland-Altman limits of agreement, and internal consistency with Rasch fit statistics, factor analysis, and Cronbach's alpha) were performed from data of an additional 312 subjects.

RESULTS

Rasch analysis demonstrated QIRC has good precision, reliability, and internal consistency (person separation, 2.03; reliability, 0.80; root-mean-square measurement error, 3.25; mean square +/- SD infit, 0.99 +/- 0.38; outfit, 1.00 +/- 0.39; item infit range, 0.70 to 1.24; and item outfit range, 0.78 to 1.32). The items (mean score, 50.3 +/- 7.3) were well targeted to the subjects (mean score, 47.8 +/- 5.5) with a mean difference of 2.45 (scale range, 0 to 100) units. Test-retest reliability (intraclass correlation coefficient, 0.88; coefficient of repeatability, +/-6.85 units), factor loading range (0.40 to 0.76), and Cronbach's alpha (0.78) also indicated the reliability and validity of QIRC.

CONCLUSIONS

The 20-item QIRC questionnaire, which quantifies the QOL of people with refractive correction by spectacles, contact lenses, and refractive surgery in the prepresbyopic age group, was developed using Rasch analysis and shown to be valid and reliable. The use of Rasch scaling allows scores to be treated as a valid continuous variable. QIRC has broad applicability for cross-sectional and outcomes research.

Validity of the childhood health assessment questionnaire is independent of age in juvenile idiopathic arthritis

OBJECTIVE

To determine whether the Childhood Health Assessment Questionnaire (CHAQ) is valid for the comparison of different age subgroups and for longitudinal studies in juvenile idiopathic arthritis (JIA).

METHODS

A CHAQ was administered to 306 children with JIA. Rasch analyses were used to compare the difficulty of each of the 30 items of the questionnaire for children of 2 age groups (> or =10 years old and <10 years old).

RESULTS

Independent of the physical disability level assessed by the Rasch model, 8 of the 30 items (27%) of the CHAQ were rated significantly different in the 2 age groups. Despite this age-related variation in item difficulty, the impact on the CHAQ disability index using its original scoring system remained low (about 0.25 points on a scale of 0-3).

CONCLUSION

The difficulty of 8 of 30 items of the CHAQ depends on the respondent's age. Nevertheless, the design of the CHAQ and its scoring system remove most of the expected physical development bias.

Short-form activity measure for post-acute care

OBJECTIVE

To develop a comprehensive set of short forms using item response theory (IRT) and item pooling procedures for the purpose of monitoring postacute care functional recovery.

DESIGN

Prospective study.

SETTING

Six postacute health care networks in the greater Boston area, including inpatient acute rehabilitation, transitional care units, home care, and outpatient services.

PARTICIPANTS

A convenience sample of 485 adult volunteers who were currently receiving skilled rehabilitation services.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

We developed a set of 6 short forms across 3 activity domains from new items and items from existing postacute care instruments.

RESULTS

Inpatient- and community-based short forms were developed for each of 3 activity domains: physical & movement, applied cognition, and personal care & instrumental. Items were selected for inclusion on the short forms to maximize content coverage and information value of items across the range of content and to minimize ceiling and floor effects. We were able to match the distribution of sample scores with very good item precision for 1 of the constructs (physical & movement); the other 2 domains (personal care & instrumental, applied cognition) were more challenging because of the variability in patient recovery and ceiling effects.

CONCLUSIONS

ITR methods and item pooling procedures were valuable in developing paired sets of short-form instruments for inpatient and community rehabilitation that provided estimates of functioning along a common metric for use across postacute care settings.