Inconclusiveness of psychometric testing of medication adherence questionnaires.

Abstract

To propose a paradigm change for the validation procedures of medication adherence questionnaires. A total of 121 validation procedures of unique questionnaires for medication adherence were analyzed. "Construct validity" and "internal consistency" were most often assessed, and test results varied largely. A more in-depth analysis indicated that the assessment of medication non-adherence included distinct but related constructs, such as the extent to which doses are missed, and the attempt to identify different facets of medication-taking behavior. Consequently, each construct requires a different measurement approach with different psychometric tests for establishing its validity and reliability. Results show that assessing the validity and reliability of adherence questionnaires with standard procedures including statistical tests is inconclusive. Refinement of the constructs of non-adherence is needed in pharmacy and medical practice. We suggest a distinction between the (i) extent of missed doses over the past 2weeks, (ii) modifiable reasons for non-adherence behavior, and (iii) unmodifiable factors of non-adherence. Validation procedures and corresponding statistical methods should be selected according to the specific single constructs.