KEY FEATURES: Examples for each statistical expression help readers understand complex formulas A chapter on how to use the literature for power analysis walks readers through the process of making good assumptions A chapter on how to write about power analysis offers 7 key points on what needs to be included in a power analysis

# The What, Why, and When of Power Analysis

### What Is Statistical Power?

Statistical power is the probability of a statistically significant test (assuming the null hypothesis is in fact false and the alternative hypothesis is true), given several factors that include the acceptable level of uncertainty, the size of the effect, the sample design, and sample size (Cohen, 1988). Power levels near zero indicate that there is little chance of detecting an effect, whereas power levels near one indicate a high probability of detecting an effect. The convention in the social sciences is to design studies with a power of at least 0.8, or an 80% chance of ...

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