Measuring the meaning of disability in rheumatoid arthritis: the Personal Impact Health Assessment Questionnaire (PI HAQ)

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Measuring the meaning of disability in rheumatoid arthritis: the Personal

Impact Health Assessment Questionnaire (PI HAQ)

S Hewlett1, A P 2 and J R Kirwan1

Background: Measurement of disability in rheumatoid arthritis is often used

to support treatment decisions and outcome assessments, but is used without

reference to the impact of disability on individual patients.

Objective: To develop and validate a scale to measure individual values for

functions, which is used to weight the level of an individual patient¹s

functional loss and thus calculate the personal impact of disability.

Methods: In four linked studies, first the phraseology for values was

explored to develop a stem question for the value scale couched in terms

patients understand (face validity). Then short and long versions of the

value scale were compared (content validity) and tests of internal

consistency and short term reliability undertaken (criterion validity).

Finally, the value scale was examined for long term reliability and

agreement with expected variables (criterion and construct validity), after

which personal impact scores were calculated and their construct validity

examined.

Results: Patients understand the concept of values, and a positively phrased

stem question was developed for the value scale, for which a short version

was reasonably equivalent to a long version. The value scale was reliable

over one week (96% changed by <1 point) with positive interitem correlation.

Reasonable six and 12 month reliability was shown (52% changed by <0.5

points), and the value scale was independent of disability and clinical,

psychological, personality, and social support variables. Personal impact

scores were then calculated by using the value scores to weight disability

scores. Impact scores varied widely between patients of similar disability.

Personal impact for disability showed convergent validity with

dissatisfaction with disability, perceived increase in disability, increased

disease activity, worse psychological status, low social support, and time

trade off for disability. It discriminated between patients with low and

high dissatisfaction with disability, life satisfaction, depression, pain,

and helplessness.

Conclusion: This individualised personal impact scale should lend meaning to

disability scores, improving the interpretation of clinical and research

data.