title: The perceived sensitivity to medicines (PSM) scale: an evaluation of validity and reliability.
abstract: OBJECTIVE
  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validity of the PSM Scale were evaluated using data collected as part of four previously published studies and one unpublished data set.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.
  
  
  CONCLUSIONS
  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.
  What is already known on this subject? It is now well understood that beliefs about medicines have an important influence on whether patients start and continue with treatment. Research spanning a range of long-term conditions and across different countries has shown that treatment uptake and adherence are consistently related to specific beliefs about prescribed medicines, such as how patients judge their personal need relative to concerns about potential adverse effects as well as more general beliefs about medicines as a class of treatment. What does this study add? The paper reports on the development and psychometric properties of a new scale to measure patients' perceptions of their sensitivity to medicines. In five studies involving different groups of individuals we found the Perceived Sensitivity to Medicines (PSM) Scale to be a reliable and valid measure. The PSM may be useful for researchers and clinicians in explaining treatment decisions, adherence and reported side-effects.
authors.affiliation: The UCL School of Pharmacy, University of London, UK. rob.horne@pharmacy.ac.uk
authors.forename: Rob
authors.initials: R
authors.lastname: Horne
authors.forename: Kate
authors.initials: K
authors.lastname: Faasse
authors.forename: Vanessa
authors.initials: V
authors.lastname: Cooper
authors.forename: Michael A
authors.initials: MA
authors.lastname: Diefenbach
authors.forename: Howard
authors.initials: H
authors.lastname: Leventhal
authors.forename: Elaine
authors.initials: E
authors.lastname: Leventhal
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Petrie
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001008:Anxiety Disorders / Q000523:psychology; D003866:Depressive Disorder / Q000523:psychology; D005260:Female; D015658:HIV Infections / Q000188:drug therapy; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D006973:Hypertension / Q000188:drug therapy; D008297:Male; D055118:Medication Adherence / Q000523:psychology*; D008875:Middle Aged; D009520:New Zealand; D011594:Psychometrics; D015203:Reproducibility of Results; D013334:Students / Q000523:psychology; D011795:Surveys and Questionnaires; D006113:United Kingdom; D014611:Vaccination / Q000523:psychology* / Q000706:statistics & numerical data; D055815:Young Adult; D016903:Drug Monitoring