University of Sydney, Sydney, Australia and
1 Imperial College London, London, UK
SIR, We read with interest the recent article by Taylor et al. [1] questioning the validity of the Disease Repercussion Profile (DRP). Research that aims to establish the construct validity of new instruments is clearly important. However, accurate identification of the constructs against which the new measure is to be compared is essential.
The DRP was developed to address a gap in the literature pertaining to the patient's perception of handicap. The World Health Organization distinguishes between the concepts of disease, impairment, disability and handicap. In rheumatoid arthritis (RA), the disease process, impairment and disability are commonly measured by such outcome measures as the erythrocyte sedimentation rate (ESR), the Ritchie Articular Index (RAI) and the Health Assessment Questionnaire (HAQ) respectively. These variables are not always strongly related. For example, in our own research we found no significant correlations between ESR and RAI or between ESR and HAQ [2]. Relationships between these concepts are complex and multiply determined, and these results cannot be taken to mean that ESR is invalid as a measure of disease activity in RA. The same is likely to be true of the relationship between patient-perceived handicap and other measures.
We would dispute some of the assumptions made as to the likely relationships between DRP scales and other measures in Taylor et al.'s [1] study. For example, expecting that RA will necessarily have less impact on the relationships of people who are married is fraught with conceptual problems. Similarly, would a strong relationship between the number of hand surgeries and the appearance subscale really be necessary to demonstrate the validity of DRP? In our unpublished data, only 19% of the sample endorsing the appearance item referred to their hands. Other effects were more commonly reported, such as a general feeling of unattractiveness (39%), concerns about weight gain (23%) and looking older (19%).
So what does the DRP measure and what relationships should we expect? Carr and Thompson [3] describe the DRP as measuring patient-perceived handicap, hence the patient's perceptions are likely to be central to the concept. One of the strongest predictors of the patient's perceptions is likely to be mood. Mood disturbance is common in RA. Hence, any study examining a measure of patient-perceived handicap should measure depression and anxiety. In our own work, we found that depression was strongly associated with all the items of DRP except finance [4]. The failure to measure depression or anxiety makes interpretation of the data extremely difficult.
It is likely that the relationships between patient-perceived handicap and other constructs are complex. However, future research can help to clarify the relationships and provide us with a better understanding of the issues that are important to individual patients.
Notes
Correspondence to: L. Sharpe, Clinical Psychology Unit, School of Psychology, University of Sydney, NSW 2006, Australia.
Accepted 17 February 2002
References
Rehabilitation Teaching and Research Unit, Wellington School of Medicine, Otago, PO Box 7343, Wellington, New Zealand and
1 University of Southampton, Southampton, UK
We thank L. Sharpe and T. Sensky for their interest in our research and share their view that future research is necessary to understand the relationships between constructs of health and well-being that may be important to individual patients. Whilst Sharpe and Sensky pose some interesting questions about factors that might lead to greatest handicap, we believe they confuse a measurement model with a structural model. We have to be reasonably sure that the measurement instruments actually are measuring the constructs of interest before looking at the way these constructs relate to each other.
It seems intuitive and certainly plausible that depression would be related to handicap, perhaps partly mediating the effects of social context and disease. However, until an adequate measurement model of handicap is established, it is very difficult to know whether correlation between measures of depression and measures of handicap is due to mediating or influencing effects (within a structural model) or whether it is due to the measures of handicap actually measuring something more similar to depression than to handicap. They pose the question So what does the DRP measure and what relationships should we expect?. Such a question can only be answered in a two-step fashion [1]. First, the measurement model must be established and validated, and only then can the constructs so measured be examined to investigate their relationship with each other. We suggest that the measurement model is not yet sufficiently established to permit adequate interpretation of correlation between the DRP and other concepts of health.
The discussion as it pertains to handicap is probably now less than relevant, given the revision of the International classification of Impairment, Disability and Handicap model, which promotes participation rather than handicap as the construct that places a person's health in a social context. It seems necessary and somewhat inevitable that we will now need to develop and evaluate measures of participation rather than handicap (sigh). However, whether such a concept is actually important or relevant to people with rheumatoid arthritis is not at all clear. Our own qualitative work suggests that we still have much to learn if we truly wish to define, measure and identify the important links between constructs that matter most to our patients [2].
Notes
Correspondence to: W. J. Taylor.
References
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