What is Power Analysis?
The Power analysis is a method for finding statistical power: the possibility of finding an effect, assuming that the effect is. To put it the other way, power is likely to dismiss a zero hypothesis when it is wrong. Note that power differs from a Type II error, which occurs when you fail to reject a false null hypothesis. So you can say that power is likely not to make your Type II error.
A Simple Example of Power Analysis
Suppose you were doing a drug test and this medicine was working. You run a series of tests with effective medication and a placebo. If you have the power of .9, it means that 90% of that time will give you statistically significant results.
In 10% of cases, your results will not be statistically significant. The power, in this case, tells you the possibility to find the difference between the two means, which is 90%. But 10% of the time, you won’t get a difference.