Several studies have found that most patients with severe mental illness (SMI) and comorbid (physical) conditions are partially or wholly nonadherent to their medication regimens. Nonadherence to treatment is a serious concern, affecting the successful management of patients with SMIs. Psychiatric disorders tend to worsen and persist in nonadherent patients, worsening their overall health. The study described herein aimed to develop and validate a scale (the Ralat Adherence Scale) to measure nonadherence behaviors in a culturally sensitive way.

Guided by a previous study that explored the primary reasons for nonadherence in Puerto Rican patients, we developed a pool of 147 items linked to the concept of adherence. Nine experts reviewed the meaning, content, clarity, and relevance of the individual items, and a content validity ratio was calculated for each one. Forty items remained in the scale’s first version. This version was administered to 160 patients (21–60 years old). All the participants had a diagnosis of bipolar disorder, major depressive disorder, or schizoaffective disorder. The STROBE checklist was used as the reporting guideline.

The scale had very good internal consistency (Cronbach’s alpha = 0.812). After a factor analysis, the scale was reduced to 24 items; the new scale had a Cronbach’s alpha of 0.900.

This adherence scale is a self-administered instrument with very good psychometric properties; it has yielded important information about nonadherence behaviors. The scale can help health professionals and researchers to assess patient adherence or nonadherence to a medication regimen.