PSY 429 Experimental Psychology

Class Exercise #7

 

Two-Way Independent-Measures Analysis of Variance

Post-Hoc Tests: Hartley's HSD Test

 

 1. The following data are from an experiment examining the extent to which different personality types are affected by distraction on a monotonous task. The number of errors committed by each individual was tabulated. Individuals were selected to represent two different personality types: introverts and extroverts. Half of the individuals in each group were tested on a monotonous task in a relatively quiet, calm room. The individuals in the other half of each group were tested in a noisy room filled with distractions.

a. Identify the independent variables and the levels of each.

b. Identify the dependent variable(s).

c. State the null hypotheses.

2. An experiment evaluated computer monitors and whether the size of the monitor or the color of the monitor made a difference in how easy to use it. The study measured the mean ease-of-use ratings given by subjects. The experimenter evaluated three different sizes (9, 12, or 15 inches) and two different colors (amber or green) in a between-subjects design.

a. Identify the independent variables and the levels of each.

b. Identify the dependent variable(s).

c. State the null hypotheses.

 

Questions 3-10 refer to the following summary table for an experiment.

3. How many levels of Factor A were there in the experiment?

4. How many levels of Factor B were there in the experiment?

5. What was the total number of subjects in the experiment?

6. How many groups were there in the experiment?

7. Assuming there were equal numbers of subjects in each group, what was the per-group sample size?

8. What is the total amount of between-group variability represented in the table (that is, what is the value of the sum of squares treatment)?

9. State the null and alternative hypotheses for the main effects of Factor A, Factor B, and the interaction.

10. Test the null hypotheses using a level of significance of .05.

11. Complete the missing entries in the summary table for a 3 x 4 factorial analysis of variance.

12. State the critical values of F that would be used to reject the null hypothesis for the main effect of Factor A, the main effect of Factor B, and the A x B interaction for a two-way independent-measures analysis of variance at an alpha level of .05 under each of the following conditions:

13. Describe when and why post-hoc tests are used.

14. Explain why you would not need to do post-hoc tests for an experiment with only k = 2 treatment conditions.

15. In an experiment with one independent variable and k = 4 treatment conditons, how many pairwise comparisons would you have to assess using the Tukey HSD test?

16. Conduct Hartley HSD tests on the following data and describe the results using a .01 level of significance.

Mean of group 1 = 3.0; mean of group 2 = 2.0; mean of group 3 = 1.0

17. An investigator was interested in the effects of gender and academic major on the number of job offers received by college seniors. The data below are from a sample of 20 males and 20 females in which the number of job offers were counted for each participant.

a. Use appropriate tests to evaluate the data.

b. Put the results into an summary table.

c. Describe the results including any descriptive statistics which would help the reader understand the results.

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