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Letter by Schwartz and Unni Regarding Article, "Ethnic Differences in 90-Day Poststroke Medication Adherence".

To the Editor: In a recent article, Lank et al prospectively followed Mexican Americans (n=692) and non-Hispanic whites (n=422) after stroke. At 90 days, participants were asked to indicate their medication adherence by answering “How often in a typical week do you miss a prescribed dose?” on a scale from never to very often. Statistical analyses found no differences in medication adherence between ethnic groups. The authors interpret the data as to suggest that medication adherence is not a unique factor that contributes to the increased recurrent stroke risk of Hispanic Americans. We question the validity of these findings for 3 reasons. First, the medication adherence measure lacked sensitivity and increased the risk of a type II error. Best practice in medication adherence research requires 2 approaches to measuring medications adherence, including a form of electronic monitoring. The single-item, interview-administered, self-report questionnaire used is one of the least reliable ways to measure medication adherence, as participants consistently inflate their medication adherence as compared with electronic monitoring. Second, the medication adherence measure lacked sensitivity to unintentional medication adherence, again increasing the risk for a type II error. In addition to missing a dose, stroke survivors may engage in other forms of poor adherence, such as taking medication incorrectly. Spanish speakers, which likely include many of the Mexican Americans in the study, as well as those with cognitive impairment, which likely include several of the stroke survivors in the study, are at an increased risk for medication errors secondary to issues around communication, cognition, and health literacy. The final threat to validity is the social desirability bias. While the authors recognized social desirability as a limitation, they made the assumption this bias would affect the data at the same intensity across ethnicities. A review of the literature indicates that social desirability demonstrates cultural differences, and therefore may not have occurred at the same rate across groups. Our opposing view to the conclusions drawn from this study is supported by the fact that large scale studies with Medicare beneficiaries using more reliable medication adherence measures consistently find differences by race and ethnicity. For example, using pharmacy refill records of over 70 000 Medicare beneficiaries, Zhang et al found that adherence to β-blockers, statins, and angiotensin-converting enzyme inhibitor or angiotensin II receptor blockers were significantly different between Hispanics and Whites. While this study is not specific to stroke survivors, these medications are commonly used to reduce both primary and secondary stroke risk. In conclusion, we commend the authors for their attention to minority health, stroke, and medication adherence, an intersection of 3 important areas of study. As researchers, we are understanding of the need to run an efficient study with currently available tools. However, we believe that the threat of a type II error was too great to support the interpretation that medication adherence is not a unique factor that contributes to the increased recurrent stroke risk of Hispanic Americans. This is especially important since there is a lack of research in medication adherence in stroke. Future research is needed that leverages best practices in research methodology, including measures of medication adherence, across the fields of stroke, medication adherence, and minority health.