Probability levels and errors



A statistical decision that must be made at the beginning of your dissertation research involves statistical probability levels and potential errors. The conventional statistical levels for rejecting the null hypothesis are either .05 or .01. One (.01) is more statistically conservative than the other (.05) because with .01 you are less willing to have your results due to chance alone. You will accept only one time in one hundred that your statistical results were due to chance. A really conservative statistical probability level is .001.

1. A Type I (Alpha) Error occurs when you statistically reject the null and it was actually true. We conclude falsely that there were statistical differences when there was none.

2. A Type II (Beta) Error occurs when you statistically accept the null and it was in fact false. We conclude that there are no statistical differences when in fact there were!

If the hypothesis is true, you statistically accept the null.

If the hypothesis is false, you statistically reject the null.

If the hypothesis is true, and you reject the null, you commit a Type I error. (The statistical probability level is liberal.)

If the hypothesis is false, and you accept the null, you commit a Type II error. (The statistical probability level is conservative.)

Return from probability levels and errors to dissertation research questions and hypotheses.