Chapter 8

beta

Beta is the probability of a Type II error.

level of significance

The level of significance is the alpha level, which measures the probability of a Type I error.

null hypothesis

The null hypothesis states that there is no effect, no difference, or no relationship.

Type I error

A Type I error is rejecting a true null hypothesis. You have concluded that a treatment does have an effect when actually it does not.

Type II error

A Type II error is failing to reject a false null hypothesis. The test fails to detect a real treatment effect.

directional test

A directional test is a hypothesis test that includes a directional prediction in the statement of the hypotheses and places the critical region entirely in one tail of the distribution.

one-tailed test

A directional test is a hypothesis test that includes a directional prediction in the statement of the hypotheses and places the critical region entirely in one tail of the distribution.

effect size

A measure of the size of the treatment effect that is separate from the statistical significance of the effect

significant

A result is said to be this, if it is very unlikely to occur when the null hypothesis is true. That is, the result is sufficient to reject the null hypothesis. Thus, a treatment has a significant effect if the decision from the hypothesis test is to reject H0.

Cohen's d

A standard measure of effect size computed by dividing the sample mean difference by the sample standard deviation.

test statistic

A statistic that summarizes the sample data in a hypothesis test. The test statistic is used to determine whether or not the data are in the critical region.

hypothesis test

A statistical procedure that uses data from a sample to test a hypothesis about a population.

alpha level

In a hypothesis test, the criterion for statistical significance that defines the maximum probability that the research result was obtained simply by chance. Also known as level of significance.

alternative hypothesis

The alternative hypothesis states that there is an effect, there is a difference, or there is a relationship.

critical region

The critical region consists of outcomes that are very unlikely to be obtained if the null hypothesis is true. The term very unlikely is defined by α.

power

The probability that the hypothesis test will reject the null hypothesis when there actually is a treatment effect.