Abstract
The concepts of effect size and statistical power are often disregarded in basic neuroscience, and most articles in the field draw their conclusions solely based on the arbitrary significance thresholds of statistical inference tests. Moreover, studies are often underpowered, making conclusions from significance tests less reliable. With this in mind, we present the protocol of a systematic review to study the distribution of effect sizes and statistical power in the rodent fear conditioning literature, and to analyze how these factors influence the description and publication of results. To do this we will conduct a search in PubMed for "fear conditioning" AND ("mouse" OR "mice" OR "rat" OR "rats") and obtain all articles published online in 2013. Experiments will be included if they: (a) describe the effect(s) of a single intervention on fear conditioning acquisition or consolidation; (b) have a control group to which the experimental group is compared; (c) use freezing as a measure of conditioned fear; and (d) have available data on mean freezing, standard deviation and sample size of each group and on the statistical significance of the comparison. We will use the extracted data to calculate the distribution of effect sizes in these experiments, as well as the distribution of statistical power curves for detecting a range of differences at a threshold of α=0.05. We will assess correlations between these variables and (a) the chances of a result being statistically significant, (b) the way the result is described in the article text, (c) measures to reduce risk of bias in the article and (d) the impact factor of the journal and the number of citations of the article. We will also perform analyses to see whether effect sizes vary systematically across species, gender, conditioning protocols or intervention types.
Highlights
BACKGROUNDBasic research in biology over the last decades has been heavily influenced by the concept of statistical significance— that is, the likelihood that a given effect size would occur by (1) that p values do not measure the magnitude of an effect and cannot be used to assess its biological significance[2] and (2) that results of significance tests are heavily influenced by the statistical power of experiments, which affects both the chance of finding a significant result for a given effect size and the positive predictive value of a given p value.[3]Effect size and power in rodent fear conditioningA quick inspection of the literature, shows that effect size and statistical power rarely receive much consideration in basic research
The biological significance of a finding can only be assessed when effect size is considered, as statistical significance by itself is dependent on statistical power, leading even small effects to yield low p values if sample size is sufficiently high
To provide an unbiased assessment of the distribution of effect sizes and statistical power in the memory literature, we will perform a systematic review of articles studying interventions that affect acquisition of fear conditioning in rodents
Summary
A quick inspection of the literature, shows that effect size and statistical power rarely receive much consideration in basic research. To provide an unbiased assessment of the distribution of effect sizes and statistical power in the memory literature, we will perform a systematic review of articles studying interventions that affect acquisition of fear conditioning in rodents. This task is appropriate for this kind of study as the vast majority of articles use the same measure to evaluate memory (i.e. percentage of time spent in freezing behaviour during a test session), allowing one to compare effects across different studies. The description of the protocol will follow the standardized format proposed by de Vries et al.[8]
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