5 or 10 response categories for the Brief Illness Perception Questionnaire: What is better?

Illness representations are important determinants of patients’ coping behaviour and health outcomes, such as treatment adherence. The Brief Illness Perception Questionnaire (Brief-IPQ) is the most useful instrument to assess illness perceptions in very ill populations. The scale includes 9 items, has good reliability and validity and patients can complete it in a few minutes. The study is devoted to the examination of two rating scales (5 and 10 response categories) of the Brief-IPQ in patients with cardiovascular disease. The Rasch methodology was used in order to test rating scale assumptions effectively. The study involved 269 patients which responded at the 10 response scale and 251 patients which responded at the 5 response scale.Results showed that the 5-level rating scale was more effective to assess illness perception than the 10-level rating scale. Furthermore, in both groups, items 4 and 7 showed problems to measure “personal control” and “comprehensibility”.