Alan Tennant

An introduction to the Rasch measurement model: an example using the Hospital Anxiety and Depression Scale (HADS).

OBJECTIVES To demonstrate the use of Rasch analysis by assessing the appropriateness of utilizing the Hospital Anxiety and Depression Scale (HADS) total score (HADS-14) as a measure of psychological distress. DESIGN Cross-sectional, using Rasch analysis. METHODS The HADS was administered to 296 patients attending an out-patient musculoskeletal rehabilitation program. Rasch analysis was conducted using RUMM2020 software to assess the overall fit of the model, the response scale used, individual item fit, differential item functioning (DIF) and person separation. RESULTS Rasch analysis supported the viability of the HADS-14 as a measure of psychological distress. It showed good person separation, little disordering of the thresholds and no evidence of DIE One anxiety item (item 11) showed some misfit to the model. The residuals patterned into the two subscales (anxiety and depression), but the person estimate derived from these two subscales was not statistically different to that derived from all items taken together, supporting the assumption of unidimensionality. A cut-point of 12 on the HADS-14 identified all cases that were classified as both anxious and depressed on the original individual HADS subscales. CONCLUSIONS The results of Rasch analysis support the use of the HADS-14 as a global measure of psychological distress. The study demonstrates the usefulness of Rasch analysis in assessing the psychometric properties of a scale and suggests that further use of this technique to assess the HADS-14 in other clinical groups is warranted.

Development of the ASQoL: a quality of life instrument specific to ankylosing spondylitis

Background: Although disease-specific health status measures are available for ankylosing spondylitis (AS), no instrument exists for assessing quality of life (QoL) in the condition. Objective: To produce an AS-specific QoL measure that would be relevant and acceptable to respondents, valid, and reliable. Methods: The ASQoL employs the needs-based model of QoL and was developed in parallel in the UK and the Netherlands (NL). Content was derived from interviews with patients in each country. Face and content validity were assessed through patient field test interviews (UK and NL). A postal survey in the UK produced a more efficient version of the ASQoL, which was tested for scaling properties, reliability, internal consistency, and validity in a further postal survey in each country. Results: A 41 item questionnaire was derived from interview transcripts. Field testing interviews confirmed acceptability. Rasch analysis of data from the first survey (n=121) produced a 26 item questionnaire. Rasch analysis of data from the second survey (UK: n=164; NL: n=154) showed some item misfit, but showed that items formed a hierarchical order and were stable over time. Problematic items were removed giving an 18 item scale. Both language versions had excellent internal consistency (α=0.89–0.91), test-retest reliability (rs=0.92 UK and rs=0.91 NL), and validity. Conclusions: The ASQoL provides a valuable tool for assessing the impact of interventions for AS and for evaluating models of service delivery. It is well accepted by patients, taking about four minutes to complete, and has excellent scaling and psychometric properties.

Assessing and adjusting for cross-cultural validity of impairment and activity limitation scales through differential item functioning within the framework of the Rasch model the pro-esor project

IntroductionIn Europe it is common for outcome measures to be translated for use in other languages. This adaptation may be complicated by culturally specific approaches to certain tasks; for example, bathing. In this context the issue of cross-cultural validity becomes paramount. ObjectiveTo facilitate the pooling of data in international studies, a project set out to evaluate the cross-cultural validity of impairment and activity limitation measures used in rehabilitation from the perspective of the Rasch measurement model. MethodsCross-cultural validity is assessed through an analysis of Differential Item Functioning (DIF) within the context of additive conjoint measurement expressed through the Rasch model. Data from patients undergoing rehabilitation for stroke was provided from 62 centers across Europe. Two commonly used outcome measures, the Mini-Mental State Examination (MMSE) and the Functional Independence Measure (FIM) motor scale are used to illustrate the approach. ResultsPooled data from 3 countries for the MMSE were shown to fit the Rasch model with only 1 item displaying DIF by country. In contrast, many items from the FIM expressed DIF and misfit to the model. Consequently they were allowed to be unique across countries, so resolving the lack of fit to the model. ConclusionsWhere data are to be pooled for international studies, analysis of DIF by culture is essential. Where DIF is observed, adjustments can be made to allow for cultural differences in outcome measurement.

Development of the PsAQoL: a quality of life instrument specific to psoriatic arthritis

Background: Patient reported outcome measures used in studies of psoriatic arthritis (PsA) have been found to be inadequate for determining the impact of the disease from the patient’s perspective. Objective: To produce the PsAQoL, a PsA-specific quality of life (QoL) instrument, employing the needs based model of QoL that would be relevant and acceptable to respondents, valid, and reliable. Methods: Content was derived from qualitative interviews conducted with patients with PsA. Face and content validity were assessed by field test interviews with a new sample of patients with PsA. A postal survey was conducted to improve the scaling properties of the new measure. Finally, a test-retest postal survey was used to identify the final measure and to test its scaling properties, reliability, internal consistency, and validity. Results: Analysis of the qualitative interview transcripts identified a 51 item questionnaire. Field test interviews confirmed the acceptability and relevance of the measure. Analysis of data from the first postal survey (n = 94) reduced the questionnaire to 35 items. Rasch analysis of data from the test-retest survey (n = 286) identified a 20 item version of the PsAQoL with good item fit. This version had excellent internal consistency (α = 0.91), test-retest reliability (0.89), and validity. Conclusions: The PsAQoL is a valuable tool for assessing the impact of interventions for PsA in clinical studies and trials. It is well accepted by patients, taking about three minutes to complete, is easy to administer, and has excellent scaling and psychometric properties.

Prevalence of low back pain in the community: implications for service provision in Bradford, UK.

STUDY OBJECTIVE: To assist a purchasing district in the planning of services for low back pain by assessing the prevalence of symptoms and the current involvement of primary, secondary, and complementary care in the treatment of low back pain. In the light of these findings, to assess further the potential impact of a new system of open access to physical therapy, as recommended by the British Clinical Standards Advisory Group (CSAG). DESIGN: A two-stage cross sectional survey approach using postal questionnaires. SUBJECTS: Altogether 1437 men and 1747 women aged 25-64 years, randomly selected from the family health services association register in Bradford. MAIN RESULTS: An annual incidence of 4.7% for low back pain was found, with lifetime, 12 month period, and point prevalences of 59%, 39%, and 19% respectively. Over a one year period, 50.3% of episodes were acute (< 2 weeks), 21% were subacute (2 weeks-3 months), and 26% were chronic (over 3 months) in duration. Altogether 17.8% of the population in this age range experienced referred pain, numbness, or tingling, and 6.4% took time off work as a result of low back pain. In the same year, 20% of the population in the same age range consulted no-one about their pain, 13.7% were treated at the primary care level, 4% received secondary care, and 3% visited a complementary therapist. One fifth of those who did not consult a professional experienced severe pain during episodes. Prevalence estimates indicate that an emphasis on early intervention and primary care management of simple low back pain as recommended by the CSAG could generate a 131% surge in demand for physical therapy. CONCLUSIONS: Local prevalence estimates may allow purchasers to estimate the potential effects of a shift in management policy for low back pain and to highlight areas of unmet need in terms of resources and patient education.

The use of outcome measures in physical medicine and rehabilitation within Europe.

The aim of the study was to survey the use of outcome measures in rehabilitation within Europe. It was envisaged that this would provide the basis for further studies on the cross-cultural validity of outcome measures. A postal questionnaire was distributed in November 1998 to 866 units providing rehabilitation. In total, 418 questionnaires were returned, corresponding to a response rate of 48%. These 418 centres treated an estimated 113,000 patients annually, undertaking 360,000 assessments. The survey focused on nine diagnostic groups: hip and knee replacement, low back pain, lower limb amputees, multiple sclerosis, neuromuscular disorders, rheumatoid arthritis, spinal cord lesions, stroke and traumatic brain injury. It identified a relatively small number of dominant outcome assessments for each diagnostic group and some variation in the preference for measures across regions. A large number of measures, however, are being used in one or a small number of locations and with relatively few patients. For rehabilitation of orthopaedic patients the majority of assessments undertaken are at the impairment level. For patients with neurological disorders the emphasis is mostly upon measures of disability.

Construct validity and reliability of the Rivermead Post-Concussion Symptoms Questionnaire

Objectives: To provide further evidence of reliability and internal and external construct validity of the Rivermead Post-Concussion Symptoms Questionnaire (RPQ), which measures severity of postconcussion symptoms following head injury. Design and setting: A cross-sectional study of consecutive patients presenting with a head injury in two urban teaching hospitals and a community trust. Patients: Three hundred and sixty-nine patients returned a questionnaire from 1689 consecutive adult patients (18 years and above) referred to radiology for a skull X-ray following a head injury, and those who were currently under the care of a community-based multidisciplinary head injury team. Method: Internal construct validity tested by fit to the Rasch Measurement model; external construct validity tested by correlations with Rivermead Head Injury Follow-up Questionnaire (RHFUQ); test-retest reliability tested by correlations at two-week intervals. Outcome measures: Rivermead Post-Concussion Symptoms Questionnaire and Rivermead Head Injury Follow-up Questionnaire. Main results: RPQ scores ranged from 0 to 64 (17.3% floor, 0.3% ceiling). Overall fit to the Rasch model was poor (item fit mean-0.416, SD=1.989, chi-squared=172.486, p < 0.01) suggesting a lack of unidimensionality. The items headaches, dizziness and forgetful displayed misfitting residuals and the first two items also displayed significant item trait fit statistics (p < 0.0006). After removing the items headaches, dizziness and subsequently nausea the RPQ demonstrated good fit at overall and individual item levels, both for the remaining 13 items (RPQ-13) and the three items (RPQ-3) which now formed a subsidiary scale. All items functioned consistently across age and gender. The RPQ-13 and RPQ-3 scales showed test-retest reliability coefficients of 0.89 and 0.72 (both p-values < 0.01) and positive correlations with RHFUQ scores (0.83 for RPQ-13, 0.62 for RPQ-3, both p-values< 0.01). Conclusions: As currently used, the RPQ does not meet modern psychometric standards. Its 16 items do not tap into the same underlying construct and should not be summated in a single score. When the RPQ is split into two separate scales, the RPQ-13 and the RPQ-3, each set of items forms a unidimensional construct for people with head injury at three months post injury. These scales show good test-retest reliability and adequate external construct validity.

A Prospective Follow-Up Study of Low Back Pain in the Community

Study Design. Opportunistic prospective follow-up study. Objective. To describe the natural history of low back pain in the community and to model the factors predictive of recovered versus persistent low back pain. Summary of Background Data. A two-phase questionnaire was mailed to adults in the Bradford Metropolitan Health District in 1994. Valid respondents were surveyed again in 1997. Analysis is based on the combined results of these two surveys. Methods. Unifactorial and multifactorial statistics were analyzed based on 1455 adults, with and without low back pain. Results. One third of respondents reported no lifetime low back pain. Average lifetime prevalence was 59% and average annual prevalence 41%. Of those who reported lifetime low back pain, 42% reported persistent annual low back pain, 18% reported a first episode in 1997, resulting in a 4% population incidence rate, and 40% reported intermittent low back pain. The likelihood of having had low back pain increased significantly with age. Those who reported a new case of low back pain in 1997 were significantly more likely to be 25–34 years of age, and these persons were most likely to report acute low back pain with very little disability. Those with persistent low back pain were significantly more likely to report chronic low back pain with some disability. Logistic regression modeling was unable to predict recovered versus persistent low back pain, given the person, pain, and treatment factors available. Conclusions. Results showed that low back pain is a mutable problem with acute episodes blending into longer periods resulting in more disability as time progresses. A wide range of demographic, pain, consultation, and treatment factors were not predictive of low back pain recovery.

Adaptation of the Functional Independence Measure for use in Turkey

Objective: To adapt the Functional Independence Measure (FIM) for use in Turkey and to assess its validity and reliability. Design: After the translation procedure, reliability was assessed using internal consistency, inter-rater reliability (kappa) and the intraclass correlation coefficient (ICC). Construct validity was tested by association with impairments and by fit of data to the Rasch model. Setting: The study was undertaken in an inpatient rehabilitation unit of the Department of Physical Medicine and Rehabilitation, Faculty of Medicine, University of Ankara. Subjects: Consecutive stroke (n = 51) and spinal cord injury (SCI) (n = 62) patients admitted for rehabilitation over a period of three years were assessed at admission and discharge. Results: Internal consistency was good for stroke, and for SCI. The level of agreement between two raters was sufficient with kappa levels of above 0.48 for SCI and above 0.44 for stroke. Minimum ICC found was 0.90. Construct validity showed expected associations with the impairment scales. However, Rasch analysis showed that bladder and bowel items compromise unidimensionality in the motor scale. Conclusion: Adaptation of the FIM has been successful and it can be used in Turkey as long as the limitations are recognized.

A Two-Element Time-Modulated Array With Direction-Finding Properties

A two-element time-modulated array system which can be configured to provide active electronic null scanning is presented. The received signal from each element of the array is time switched and combined to provide a phase-modulated output in which the depth of modulation is dependent on the angle of arrival of the received signal. The angular response of the array at the first harmonic of the switching frequency exhibits a deep null which can be scanned in angle to plusmn90deg by controlling the mark-space ratio of the element switching waveform