PT  - JOURNAL ARTICLE
AU  - Clarissa F. D. Carneiro
AU  - Thiago C. Moulin
AU  - Malcolm R. Macleod
AU  - Olavo B. Amaral
TI  - Effect size and statistical power in the rodent fear conditioning literature – a systematic review
AID  - 10.1101/116202
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 116202
4099  - http://biorxiv.org/content/early/2017/03/14/116202.short
4100  - http://biorxiv.org/content/early/2017/03/14/116202.full
AB  - Proposals to increase research reproducibility frequently call for focusing on effect sizes instead of p values, as well as for increasing the statistical power of experiments. However, it is unclear to what extent these two concepts are indeed taken into account in basic biomedical science. To study this in a real-case scenario, we performed a systematic review of effect sizes and statistical power in studies using rodent fear conditioning, a widely used behavioral task to evaluate learning and memory. Our search criteria yielded 410 experiments comparing control and treated groups in 122 articles. Interventions with statistically significant differences had a mean effect size of 45.6%, and amnesia caused by memory-impairing interventions was nearly always partial. Mean statistical power to detect the average effect size observed in well-powered experiments (37.2%) was 65%, and was lower in studies with non-significant results. Only one article reported a sample size calculation, and our estimated sample size to achieve 80% power considering typical effect sizes and variances (15 animals per group) was reached in only 12.2% of experiments. Effect size correlated with textual descriptions of results only when findings were non-significant, and neither effect size nor power correlated with study quality indicators, number of citations or impact factor of articles. In summary, effect sizes and statistical power have a wide distribution in the rodent fear conditioning literature, but do not seem to have a large influence on how results are described or cited. Failure to take these concepts into consideration might limit attempts to improve reproducibility in this field of science.