Development of a multimorbidity illness perceptions scale (MULTIPleS)

Abstract

Background: Illness perceptions are beliefs about the cause, nature and management of illness, which enable patients to make sense of their conditions. These perceptions can predict adjustment and quality of life in patients with single conditions. However, multimorbidity (i.e. patients with multiple long-term conditions) is increasingly prevalent and a key challenge for future health care delivery. The objective of this research was to develop a valid and reliable measure of illness perceptions for multimorbid patients.

Methods: Candidate items were derived from previous qualitative research with multimorbid patients. Questionnaires were posted to 1500 patients with two or more exemplar long-term conditions (depression, diabetes, osteoarthritis, coronary heart disease and chronic obstructive pulmonary disease). Data were analysed using factor analysis and Rasch analysis. Rasch analysis is a modern psychometric technique for deriving unidimensional and intervally-scaled questionnaires.

Results: Questionnaires from 490 eligible patients (32.6% response) were returned. Exploratory factor analysis revealed five potential subscales 'Emotional representations', 'Treatment burden', 'Prioritising conditions', 'Causal links' and 'Activity limitations'. Rasch analysis led to further item reduction and the generation of a summary scale comprising of items from all scales. All scales were unidimensional and free from differential item functioning or local independence of items. All scales were reliable, but for each subscale there were a number of patients who scored at the floor of the scale.

Conclusions: The MULTIPleS measure consists of five individual subscales and a 22-item summary scale that measures the perceived impact of multimorbidity. All scales showed good fit to the Rasch model and preliminary evidence of reliability and validity. A number of patients scored at floor of each subscale, which may reflect variation in the perception of multimorbidity. The MULTIPleS measure will facilitate research into the impact of illness perceptions on adjustment, clinical outcomes, quality of life, and costs in patients with multimorbidity.

Figure 1. Person distribution for ‘Emotional Representations’ Scale.

A large group of patients, represented by bars above the x-axis, fall between −1.6 and −3.2 logits, which were outside the measurable range of the scale, represented below the x-axis of the figure.

Figure 2. Category response thresholds for item 30.

Disordered response thresholds are evident for item 30.

Figure 3. Category response options for item 26.

Following rescoring, response thresholds are correctly ordered for item 26.

Figure 4. Illustration of logit (i.e. perceived importance of multimorbidity) value for each subtest in the Summary scale.

When measured along the same linear continuum (perceived importance of multimorbidity) mean location of each subscale can be directly compared. By convention, in Rasch analysis the Summary Scale is centred around zero logits.

Figure 5. Analysis summary.