Claims and statistical inference in animal physical cognition research.

Twenty years after Povinelli’s “Folk Physics for Apes”, this paper assesses how researchers have made claims about animal physical cognition, and the statistical inferences that have been used to support them. These data are relevant in light of the current replicability issues facing science. We surveyed 116 published experiments from 63 papers on physical cognition, which included data from 43 different species of animals. Across these experiments most sample sizes were small, with often fewer than 10 animals being tested. However, in contrast to related psychological disciplines, we found that only 62% of our sample of physical cognition research made positive claims. This suggests that animal physical cognition does not have a strong publication bias towards positive results. Furthermore, we found evidence that researchers are making many true statistical inferences at the individual level, i.e. whether individual animals pass certain tests of physical cognition or not. In contrast, the strength of evidence of statistical effects at the group level was weaker and consistent with many effect sizes being overestimated. Overall, our analysis provides a cautiously optimistic analysis of reliability and bias in animal physical cognition research, however it is nevertheless likely that a non-negligible proportion of results will be difficult to replicate.