PSY 429 Experimental Psychology

Class Exercise #5

Analysis of Variance

1.An experiment examined the effects of caffeine on memory. Memory scores were compared between a group given caffeine and a group given a placebo.

a. How many independent variables are there?

b. Identify the independent variable(s) and the levels of each.

c. Identify the dependent variable(s)?

d. State the null hypothesis (if only 1) or hypotheses (if more than 1).

 

2. A study examined the effects of four doses of a new drug on symptoms of schizophrenia.

a. How many independent variables are there?

b. Identify the independent variable(s) and the levels of each.

c. Identify the dependent variable(s)?

d. State the null hypothesis (if only 1) or hypotheses (if more than 1).

 

3. A study compared brain development (i.e. weight of cortex) of rats as a function of the effects of a positive, challenging, and diverse environment (called an enriched environment) with an environment that is relatively impoverished and isolated for two different species of rats, "hooded" rats and "Sprague-Dawley" rats.

a. How many independent variables are there?

b. Identify the independent variable(s) and the levels of each.

c. Identify the dependent variable(s)?

d. State the null hypothesis (if only 1) or hypotheses (if more than 1).

 

4. An experiment was designed to examine the effects of a new antianxiety drug (versus a placebo) on male and female college students who were previously identified as either low or high in text anxiety.

a. How many independent variables are there?

b. Identify the independent variable(s) and the levels of each.

c. Identify the dependent variable(s)?

d. State the null hypothesis (if only 1) or hypotheses (if more than 1).

 

5. Consider the following scores in an experiment involving three groups, A, B, and C, with five subjects in each group.

Without actually computing the sum of squares error term (SS_error), what must its value be? Why?

 

6. What does a mean square represent in analysis of variance?

7. State the critical value of F that would be used to reject the null hypothesis for a one-way between-subjects analysis of variance at an alpha level of .05 under each of the following conditions:

a. k = 3, n = 21

b. k = 4, n = 20

c. k = 3, n = 30

d. k = 5, n = 75

8. In a one-way between-subjects analysis of variance, what are the possible sources of between-groups variability?

9. In a one-way between-subjects analysis of variance, what are the possible sources of within-groups variability?

9. Under what circumstances will the F ratio, over the long run, approach 1.00? Under what circumstances will the F ratio, over the long run, be greater than 1.00?

10. Complete the missing entries in the ANOVA summary table for a one-way analysis of variance having 3 levels of the independent variable and n = 30 per group.

11. Complete the missing entries in the ANOVA summary table for a one-way analysis of variance having 4 levels of the independent variable.

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