Question

Does stress affect the recall ability of police eyewitnesses? This issue was studied in an experiment that tested eyewitness memory a week after a nonstressful interrogation of a cooperative suspect and a stressful interrogation of an uncooperative and belligerent suspect. The numbers of details recalled a week after the incident was recorded, and the summary statistics are given below (based on data from “Eyewitness Memory of Police Trainees for Realistic Role Plays,” by Yuille, et al., Journal of Applied Psychology, Vol. 79, No. 6). Use a 0.01 significance level to test the claim in the article that “stress decreases the amount recalled.” USE THE CONFIDENCE INTERVAL METHOD FOR THIS PROBLEM!! Nonstress: n = 40, x = 53.3, s = 11.6 Stress: n = 40, x = 45.3, s = 13.2

Answer 1

Hypothesis:

Since alternative hypothesis is less than type lower limit of confidence interval is minus infinity. Now we find upper limit of 95% confidence interval,

we assume equal variance.

Degrees of freedom = n1 + n2 -2 = 40+40-2 = 78

Thus confidence interval is . This interval does not contain zero, hence we reject null hypothesis at 5% level of significance and conclude that stress decreases the amount recalled.