In their article ‘Is cognitive functioning impaired in methamphetamine users? A critical review,’ Hart et al (2011) present a provocative view of the literature on methamphetamine abuse and cognition to date, parting in their conclusions from previous reviews, which have tended to suggest that methamphetamine abuse is associated with significant cognitive abnormalities. In contrast, Hart et al suggest that such deficits have, in fact, only been documented in a minority of cases, and that the assumptions held by the field may have resulted from poorly worded or conflated interpretations of the evidence rather than consistent or convincing findings, to the potential detriment of treatment and policy decisions.

The concerns expressed by Hart et al are certainly well justified, and the article is a much-needed wake-up call to the field, as the authors flag a number of important methodology and data interpretation problems plaguing current research. Among their most poignant criticisms is the language conventionally used in interpreting and discussing findings, as studies comparing methamphetamine-abusing and control subjects often interpret any statistical difference in scores as clinically significant, resulting in overstated conclusions that often overreach the actual data. That is, studies tend to confound the definitions of statistical significance and clinically significant impairment, and assume that differences in cognitive test scores reflect a meaningful difference in real-life outcomes. In articulating this perspective and exposing the tendency of the field to report more severe deficits than are warranted by the data, the authors encourage more critical reading of previous literature and raise the bar for future studies—a service to the field as it moves forward.

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