Determinants of medication adherence in people living with Parkinson’s: psychometric testing of a questionnaire based on the theoretical domains framework

Abstract Introduction Medication adherence is a critical determinant of health outcomes and quality of life in people living with Parkinson’s. It is estimated that up to 65% of people diagnosed with Parkinson’s in the UK are non-adherent,[1] yet existing measures do not consider specific factors which can hinder or support medication-taking behaviours in this population. This study builds on previous qualitative research to explore the barriers and facilitators for medication adherence in people with Parkinson’s, utilising the Theoretical Domains Framework (TDF).[2] Aim To test the psychometric properties of the Parkinson’s-specific medication adherence questionnaire (P-MAQ)—a theoretically informed measure based on the TDF. Methods An online Qualtrics survey was distributed to a convenience sample of people with a formal diagnosis of Parkinson’s. Participants were recruited through an advert shared by Parkinson’s UK in June/July 2025. Participants completed the P-MAQ—a 102-item questionnaire split across the 14 domains of the TDF, rating the barriers and facilitators to medication adherence against a 5-point Likert scale (strongly disagree to strongly agree). Item generation was informed by previous qualitative research,[2] and wording was refined based on feedback from a range of stakeholders (including patients, carers, pharmacists, health psychologists, Parkinson’s specialists and experts in questionnaire design) across four previous iterations of the questionnaire. Exploratory factor analysis (EFA) was conducted using Statistical Package for Social Sciences (SPSSv29), and Cronbach’s alpha testing was used to establish the internal reliability of scales. Results A total of 86 respondents completed all questions. Most participants lived in England (88.4%). The most frequently reported age was 71–80 (36%) and 61–70 (35%) years old. Most lived at home with family (65%). EFA identified six factors within the P-MAQ, which encompassed all 14 domains of the TDF (71-items in total). These were labelled: 1) Intentions, Motivation and Goal Orientation (19-items); 2) Perceived Effort and Self-belief (20-items); 3) Knowledge of Medications and Potential Consequences (12-items); 4) Practical Knowledge of Medication (9-items); 5) External Barriers and Accessibility (6-items); and 6) Social Support (5-items). All sub-scales demonstrated acceptable Cronbach alpha values (alpha coefficients= > 0.770) indicating excellent internal consistency of the revised P-MAQ sub-scales. Conclusion Findings suggest that the revised P-MAQ provides a psychometrically robust, Parkinson’s-specific measure of the determinants of medication adherence, capturing a wide range of barriers and facilitators that are unique to this patient group. This shortened version of the P-MAQ (from 102 to 71 items) provides a more acceptable measure for completion, leading to improved face validity of its use in future research. Further correlational analysis is needed to test the construct validity of the P-MAQ by exploring associations with existing measures of medication adherence. Study limitations relate to the low ratio of participants (n = 86) to variables (n = 102). Future research will aim for a 5:1 ratio (n = 355 participants: n = 71 P-MAQ variables) to ensure that the appropriate statistical assumptions are met. More research is needed to test the application of the P-MAQ in clinical practice to support tailored, patient-centred care and design interventions to improve medication adherence of people living with Parkinson’s.