Psychology Statistics ANOVA
Psy2100 Statistical Methods Name: ______________

Assignment 7

Please show your work, neatly and in enough detail for us to give partial credit when due.

1. The following data are from an experiment comparing illness symptoms for 3 treatment conditions with a separate sample of n = 5 in each treatment. These are the data from the groups.

Treatment

Treatment

Treatment

T = 45

Group 1

Group 2

Group 3

∑X2 = 229

M1 = 1

M2 = 2

M3 = 6

N = 15

SS1 = 4

SS2 = 10

SS3 = 10

k = 3

Using an ANOVA, test whether there are any significant differences among the 3 treatments (α = .05).

a. Define hypotheses (1 point)

b. Find the critical value/region. (1 point)

c. Calculate the test statistic (1 point)

Source

SS

df

MS

F

Between

Within

Total

d. Make a decision regarding the hypothesis based on your results and write a conclusion statement summarizing the results. (1 point)

e. Given the results, what would be an appropriate next step for the analysis? (You don’t need to calculate anything, just state what you would do given what you found in 1d above.) (1 point)

2. Researchers were interested in whether certain health behaviors can reduce the number of sick days employees take. Employees were randomly assigned to three groups, with a separate sample of n = 10 in each group. Group 1 was asked to eat 5 servings of fruits and vegetables a day for a year. Group 2 was asked to eat 5 servings of fruits and vegetables a day, as well as exercise 5 times a week, for a year. Group 3 served as the control group and was not asked to change their behaviors. At the end of the year, the number of sick days were compared.

Healthy Diet

Healthy Diet & Exercise

Control

T = 156

∑X2 = 860

M1 = 5

M2 = 4.4

M3 = 6.2

N = 30

SS1 = 10

SS2 = 10.4

SS3 = 11.8

k = 3

a. Define hypotheses (1 point)

b. Using the dataset provided to you, conduct a one-way ANOVA in SPSS. This means you will have SPSS conduct the test just specified above, comparing the number of sick days for the 3 groups. Under Analyze, select Compare Means > One-Way ANOVA. Put the Group variable as the Factor and the Sick_Days variable under the Dependent List. Click OK. Paste your output below. (2 points)

c. Using = .05, make a decision regarding the hypothesis based on the output (the “Sig.” value) and write a conclusion statement summarizing the results. (The “Sig.” value in the output tells you the probability of obtaining the observed group differences under the null.) (1 point)

3. When researchers are interested in finding differences among 3 or more groups, why don’t they use a bunch of t-tests to look for differences for each possible pair of means/groups? (1 point)

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