The perceived sensitivity to medicines (PSM) scale: An evaluation of validity and reliability.

Objectives
We report on the development and psychometric properties of a scale to measure perceived sensitivity to medicines (PSM).

Design
The internal consistency, test–retest reliability, criterion-related, and predictive validity of the PSM Scale were evaluated using data collected as part of four previously published studies and one unpublished data set.

Methods
Participants (n= 1,166) included patients receiving treatment for HIV infection and hypertension, individuals receiving a travel vaccination, and undergraduate students. Criterion-related validity was assessed by examining associations between the PSM and beliefs about medicines (Beliefs about Medicines Questionnaire), anxiety and depression (Hospital Anxiety and Depression Scale). Predictive validity was assessed by examining associations between the PSM and medication adherence and with symptom reports following vaccination. Test–retest reliability was assessed in an undergraduate sample who completed the PSM on two occasions, 2 weeks apart.

Results
Test–retest reliability was high (r= .89, p < .001). Cronbach’s alpha ranged from 0.79–0.94. Consistent with expectations, high PSM scores were associated with negative beliefs about medicines in general, strong concerns about potential adverse effects of prescribed medicines, and doubts about the necessity for treatment. High PSM scores predicted non-adherence to anti-retroviral therapy and a higher incidence of symptoms following vaccination.

Conclusion
The findings present preliminary evidence that the PSM is a valid and reliable measure of perceived sensitivity to medication. While further work is needed to develop and evaluate the scale, the findings support its use as a research tool in studies of the use and effects of medicines.