What is a Type I error? A Type II error?
A Type I error occurs when you reject a true
null hypothesis or when you think you have found a
difference; but, in reality, there is not one. It is equal
to the p value when you reject the null hypothesis.
A Type II error is when you fail to reject the
null hypothesis when there is in fact a difference
between groups. In this text, we do not compute
the exact probability of a Type II error.