Influence of the mode of administration on the results of medication adherence questionnaires

Adherence to medication regimen is commonly assessed through questionnaires, some of which are validated via self-administration. The inadequate health literacy of elderly people pushes researchers to the use of interviews as a method of administration. The aims of this study were to compare the results obtained with an interviewer-administered and a self-administered medication adherence questionnaire and to evaluate the consequences of the adherence status classification of individuals.

A cross-sectional study was performed in which the Medida de Adesão aos Tratamentos adherence questionnaire was administered to adult patients who were taking at least 1 antihypertensive drug. The data were collected in 7 community pharmacies in central Portugal between March 2014 and September 2015 in 2 different phases: in the first phase, the questionnaire was applied during a healthcare professional interview, and the second phase involved a self-report administration. A confirmatory factor analysis was conducted, and the measurement and structural invariances across the application methods were examined.

A sample of 425 patients with a mean age of 68.21 ± 10.56 years participated in the study. The confirmatory factor analysis revealed that both the interview and self-report had a good fit with the original model, although the self-report results exhibited a better fit. In the interview administration, we obtained lower values for skewness and higher levels of kurtosis. The patients subjected to the interview administration presented with a 9.7% higher tendency to answer "never" when compared with the self-administered application, which overestimated adherence.

The interview administration method induced bias that led to a higher percentage of "never" answers and a subsequent overestimation of adherence levels. Self-report administration should be preferred in the application of medication adherence questionnaires.