POWER ANALYSIS Power analysis is a procedure that allows a number of parameter estimates to be made from sample data. In general, the purpose is to determine whether or not any given sample contains enough subjects, given the chosen power, alpha, and effect size, to determine a false null hypothesis in the target population. As well, the number of subjects required for a specific study can be estimated given a specific alpha, effect size, and power requirement. The estimates can be made either A Priori– before the data are collected, or Post Hoc– estimated from existing studies. Typical ranges for statistical power are from 0 – 1 with smaller numbers suggesting very little power, and numbers closer to 1 suggesting greater power. As in conventional effect size estimates, power statistics are expressed as decimals with 0 - .20 suggesting very low power, .20 - .50, low to moderate power, .50 - .80, moderate to high power, and .80 and above, strong power.