Introduction to Power
Prerequisites
Significance
Testing,
Type I and Type II Errors, Misconceptions
Learning Objectives
 Define power
 Identify situations in which it is important to estimate power
Power is defined as the probability of correctly
rejecting a false null hypothesis. In terms of our example, it
is the probability that given there is a difference between
the population means of the new method and the standard method,
the sample means will be significantly different. The probability
of failing to reject a false null hypothesis is often referred
to as β.
Therefore power can be defined as:
power = 1  β.
It is very important to consider power while designing
an experiment. You should avoid spending a lot of time and/or
money on an experiment that has little chance of finding a significant effect.
