Question

10. Albert Bandura has conducted a studies on aggression in children. In one study (Bandura, Ross, & Ross, 1963), 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 num- ber 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 NO FILM GROUP 5 20 0 20 65 41 80 52 35 15 75 60 50 47 33 10 8 30 13 0 25 (a) State formally the hypotheses necessary to conduct a directional test of no difference be- tween the two population means. (b) Com- plete the test at the .01 level of significance, and state your conclusion. (c) Compute the estimated effect size, g, and

Answer 1

Ho :   µ1 - µ2 =   0                  
Ha :   µ1-µ2 >   0                  
                          
Level of Significance ,    α =    0.01                  
                          
Sample #1   ---->   sample 1                  
mean of sample 1,    x̅1=   47.75                  
standard deviation of sample 1,   s1 =    20.28                  
size of sample 1,    n1=   12                  
                          
Sample #2   ---->   sample 2                  
mean of sample 2,    x̅2=   12.33                  
standard deviation of sample 2,   s2 =    10.69                  
size of sample 2,    n2=   9                  
                          
difference in sample means =    x̅1-x̅2 =    47.7500   -   12.3   =   35.42  
                          
pooled std dev , Sp=   √([(n1 - 1)s1² + (n2 - 1)s2²]/(n1+n2-2)) =    16.9150                  
std error , SE =    Sp*√(1/n1+1/n2) =    7.4588                  
                          
t-statistic = ((x̅1-x̅2)-µd)/SE = (   35.4167   -   0   ) /    7.46   =   4.748
                          
Degree of freedom, DF=   n1+n2-2 =    19                  

p-value =        0.000070   [excel function: =T.DIST.RT(t stat,df) ]              
Conclusion:     p-value <α , Reject null hypothesis  

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