Evidence of HARKing in mouse behavioural tests of anxiety

Over the last decades, behavioural tests in animals, especially rodents, have been a standard screening method to determine the mechanisms of action and efficacy of psychopharmacological compounds. Yet, recently the reproducibility of some of these tests has been questioned. Based on a systematic review of the sensitivity of mouse behavioural tests to anxiolytic drugs, we analysed behavioural outcomes extracted from 206 studies testing the effect of diazepam in either the open-field test or the hole-board test. Surprisingly, we found that both the rationale given for using the test, whether to detect anxiolytic or sedative effects, and the predicted effect of diazepam, anxiolytic or sedative, strongly depended on the reported test results. The most likely explanation for such strong dependency is post hoc reasoning, also called hypothesizing after the results are known (HARKing). HARKing can invalidate study outcomes and hampers evidence synthesis by inflating effect sizes. It may also lead researchers into blind alleys, and waste animals, time and resources for inconclusive research.