Question

1. In a classic study of infant attachment, Harlow (1959) placed infant monkeys in cages with two artificial surrogate mothers. One “mother” was made from bare wire mesh and contained a baby bottle from which the infants could be fed. The other mother was made from soft terry cloth and did not provide any access to food. Harlow observed the infant monkeys and recorded how much time per day they spent with each mother. In a typical day, the infants spent a total of 18 hours clinging to one of the two mothers. If there were no preference between the two, you would expect the time to be divided evenly, with an average µ = 9 hours for each of the mothers. However, the typical monkey spent around 15 hours per day with the terry-cloth mother, indicating a strong preference for the soft, cuddly mother. Suppose a sample of n = 25 infant monkeys averaged M = 15.3 hours per day with SS = 1800 with the terry-cloth mothers. Is this result sufficient to concluded that the monkeys spent significantly more time with the

softer mother than would be expected if there were not preference? Use a one-tailed test with α = .01.

a. State the null hypothesis in words and in a statistical form

b.State the alternative hypothesis in words and a statistical form

c. Compute the appropriate statistic to test the hypotheses. Sketch the distribution with the estimated standard error and locate the critical region(s) with the critical value(s)

d. State your statistical decision

e. Compute Cohen’s d. Interpret what this d really means in this context

f. What is your conclusion? Interpret the result. Don’t forget to provide statistical information as well (e.g., t-score, df, α, Cohen’s d)

Answer 1