Larsen and Kozar (2005) investigated the effectiveness of a computer administered alcohol education program for college students who had been disciplined for alcohol abuse on campus. The participants were administered a questionnaire that asked about their intentions regarding future use of alcohol. This questionnaire was administered before the participants completed the alcohol education program and again after they completed the program. Higher questionnaire scores indicate a greater willingness to change current drinking behaviors. The questionnaire scores shown below are similar to those obtained by Larsen and Kozar.

Pre-intervention score (X₁) ....................................... Post-intervention score (X₂)
36 ............................................................................................... 37
39 ............................................................................................... 40
42 ............................................................................................... 41
34 ............................................................................................... 36
36 ............................................................................................... 37
32 ............................................................................................... 31
29 ............................................................................................... 30
30 ............................................................................................... 30
31 ............................................................................................... 32

Using these scores, carry out a t test for two related samples. Follow the steps shown below.

1. Present the null and alternative hypothesis. Assume that the researchers will carry out a one-tailed test and that they expect the pre-intervention scores to be lower than the post-intervention scores.

2. Calculate the degrees of freedom.

3. Use Table B to identify the critical t value for alpha set equal to .05.

4. Present the decision rule.

5. Calculate D̅.

6. Calculate SS_D.

7. Calculate s_D.

8. Calculate the standard error, s_D̅.

9. Calculate the observed t ratio.

10. Present a statistical decision.

11. Interpret the result in the context of the research situation.