Personality and aggressive behavior. How does personality impact aggressive behavior? A team of university psychologists conducted a review of studies that examined the relationship between personality and aggressive behavior (Psychological Bulletin, Vol. 132, 2006). One variable of interest to the researchers was the difference between the aggressive behavior level of individuals in the study who scored high on a personality test and those who scored low on the test. This variable, standardized to be between -7 and 7, was called ‘‘effect size.''

(A large positive effect size indicates that those who score high on the personality test are more aggressive than those who score low.) The researchers collected the effect sizes for a sample of n = 109 studies published in psychological journals. This data are saved in the PERAGGR file. A dot plot and summary statistics for effect size are shown in the accompanying MINITAB printouts (bottom of p. 40). Of interest to the researchers is the true mean effect size μ for all psychological studies of personality and aggressive behavior.

(a) Identify the parameter of interest to the researchers.

(b) Examine the dot plot. Does effect size have a normal distribution? Explain why your answer is irrelevant to the subsequent analysis.

(c) Locate and interpret a 95% confidence interval for μ on the accompanying printout.

(d) If the true mean effect size exceeds 0, then the researchers will conclude that in the population, those who score high on a personality test are more aggressive than those who score low. Can the researchers draw this conclusion? Explain.