Question

Albert Bandura has conducted a number of studies on aggression in children. In one study, one group of nursery school children were shown a film of adults punching, hitting (with a hammer), kicking, and throwing a large rubber Bobo doll. Another group was not shown the film. Afterward, both groups were allowed to play with Bobo dolls in a playroom, and the number of violent contacts were measured in each child. Let us imagine that we replicated this study and obtained the following data :scores are the number of violent contacts with the Bobo doll): Film Group: 20, 65, 41,80,52,35, 15, 75,60,50,47,33 No Film Group: 5,20, 0,0,10, 8, 30, 13,0,25 a) State formally the hypotheses necessary to conduct a directional test of no difference between the two population means. b) Complete the test at the .01 level of significance, and state your conclusion.

Answer 1

Albert Bandura has conducted a number of studies on aggression in children. In one study, one group of nursery school children were shown a film of adults punching, hitting (with a hammer), kicking, and throwing a large rubber Bobo doll. Another group was not shown the film. Afterward, both groups were allowed to play with Bobo dolls in a playroom, and the number of violent contacts were measured in each child. Let us imagine that we replicated this study and obtained the following data :scores are the number of violent contacts with the Bobo doll): Film Group: 20, 65, 41,80,52,35, 15, 75,60,50,47,33 No Film Group: 5,20, 0,0,10, 8, 30, 13,0,25

a) State formally the hypotheses necessary to conduct a directional test of no difference between the two population means.

Two tailed test

b) Complete the test at the .01 level of significance, and state your conclusion.

Calculated t=5.1276

DF = n₁+n₂-2 =20

Table value of t with 20 DF at 0.01 level = 2.8453

Rejection Region: Reject Ho if t < -2.8453 or t > 2.8453

Calculated t = 5.1276, falls in the rejection region

The null hypothesis is rejected.

We conclude that there is significant difference between the two population means.

Pooled-Variance t Test for the Difference Between Two Means
(assumes equal population variances)
Data
Hypothesized Difference	0
Level of Significance	0.01
Population 1 Sample
Sample Size	12
Sample Mean	47.75
Sample Standard Deviation	20.2759
Population 2 Sample
Sample Size	10
Sample Mean	11.1
Sample Standard Deviation	10.8059
Intermediate Calculations
Population 1 Sample Degrees of Freedom	11
Population 2 Sample Degrees of Freedom	9
Total Degrees of Freedom	20
Pooled Variance	278.6575
Standard Error	7.1475
Difference in Sample Means	36.6500
t Test Statistic	5.1276
Two-Tail Test
Lower Critical Value	-2.8453
Upper Critical Value	2.8453
p-Value	0.0001
Reject the null hypothesis