The Intentional Non-Adherence Scale (INAS): Initial development and validation

Objective: Adherence continues to be a major challenge in healthcare but there is still limited understanding of all the factors which can influence adherence behaviour. The present study was designed to identify a range of factors associated with intentional non-adherence and to see if they could be formed into a psychometrically sound scale. Methods: Patients in three different clinical groups (Hypertension (N = 175); Oncology (N = 115); Gout (N = 196)) were given the new scale together with an adherence self-report and/or biomarker measure. Other, more established measures of factors known to be associated with adherence (BMQ, PAM, BIPQ), were also completed by patients for comparative and validation purposes. Exploratory Factor Analysis (EFA) was conducted to examine the factor structure of the new scale, and other statistical analyses were used for testing the psychometric properties of the new scale. Results: EFA revealed two factors, which were labelled "Resisting illness" and "Testing treatment'. Both scales were found to have good psychometric properties and explained unique variance in adherence in all three clinical groups. Conclusion: This new scale shows promise in describing and explaining some relatively novel factors underlying treatment non-adherence. Further work in different patient groups and clinical contexts is needed to confirm the factor structure and predictive value of these scales.