Power Failure

Say you're poring over a brain imaging study that's making a hot new claim. If it has the power of an average neuroscience study, the odds that its findings are actually true are 50-50 or lower, according to a report in the MayNature Reviews Neuroscience.A study sample, by definition, is a slice of reality. With the proper statistical number crunching, researchers can quantify the likelihood that a pattern seen in a sample occurs in the real world.Statistical power — the probability that a study will find an effect if one actually exists — depends on two factors: sample size and effect size.In a brain imaging study that's looking for a telltale autism signature, for example, the sample size is the total number of participants, and the effect size is the difference in brain activity between the autism and control groups.If a study has a small sample size, it needs to find a moderate-to-large effect in order to surpass the power threshold for statistical significance.What surprised me, however, is that even when a small study finds a statistically significant effect, it's more likely to be false than a finding from a large study.Read more at...SFARI.org, May 2013.