ARE WE MAKING THE MOST OF THE STANFORD HEALTH ASSESSMENT QUESTIONNAIRE

For many years, the Stanford Health Assessment Questionnaire (HAQ) has provided an effective measure of disability. Recently, some debate ha s emerged about whether or not the HAQ is an 'ordinal' or 'interval' s cale. The opportunity to test its level of measurement arose when the scale was applied in a community survey which undertook a two-stage ra ndom sample using postal questionnaires to ascertain the health care n eeds of those with arthritis. The HAQ data are fitted to the Rasch mod el which tests for the presence of certain desirable characteristics o f measurement, e.g. unidimensionality. The fit of the data to the mode l for those self-reporting rheumatoid arthritis (RA) was adequate. The transformed HAQ score, derived from the Rasch analysis, is compared w ith the ordinary HAQ (raw) score. This shows that, for those with RA, incremental units of the raw score at the margins of the scale reflect an increasing level of (dis)ability compared to similar units in the centre of the scale. Thus, the traditional HAQ score (range 0-3) is an ordinal score. The findings also indicate that scoring all 20 items m ay lead to greater sensitivity. Questions are also raised about the co nstruct validity for those with other types of arthritis. For osteoart hrosis, the grip item does not appear to belong to the same underlying construct as the other items.