What is a missed dose? Implications for construct validity and patient adherence.

The construct 'missed dose' is central to many assessments of medication adherence. However, few studies have investigated how patients or clinicians conceptualize missed doses or the extent of the concordance or discordance between clinicians and patients. To address this gap we conducted semi-structured interviews with 45 sero-positive African American adults taking HAART and 17 of their clinicians. Results reveal large variability in missed dose conceptions among both patients and physicians and significant differences between the two groups. Overall, patients reported a stricter definition of missed dose than did clinicians. Fifty-five percent of patients thought that a pill-taking delay of six hours beyond the prescribed dosing time constituted a missed dose, by comparison, only one physician agreed with this assessment. More than one-third of patients thought that the proper response to a missed dose would be to skip it altogether, but only about 12% of clinicians agreed. These findings have implications for the construct validity of self-report measures of adherence, for patient adherence behaviours based on missed dose conceptions and for patient-physician relationships and communication within the clinical environment.