Chapter 21

Question 1

Alpha Level

Answer 1

The threshold P-value that determines when we reject a null hypothesis. If we observe a statistic whose P-value based on the null hypothesis is less than alpha , we reject that null hypothesis.

Question 2

Statistically Significant

Answer 2

When the P-value falls below alpha level, we say that the test is “statistically significant” at that alpha level.

Question 3

Significance Level

Answer 3

The alpha level is also called the significance level, most often in a phrase such as a conclusion that a particular test is “significant at the 5% significance level.”

Question 4

Type I Error

Answer 4

The error of rejecting a null hypothesis when it is in fact true (also called a “false positive”). The probability of a Type I Error is alpha.

Question 5

Type II Error

Answer 5

The error of failing to reject a null hypothesis when in fact it is false (also called a “false negative”). The probability of a Type II Error is commonly denoted as beta and depends on the efect size.

Question 6

Power

Answer 6

The probability that a hypothesis test will correctly reject a false null hypothesis is the power of the test. To find power, we must specify a particular alternative parameter value as the “true” value. For any specific value in the alternative, the power is 1-beta.

Question 7

Effect Size

Answer 7

The difference between the null hypothesis value and tru value of a model parameter is called the effect size.