1. Last fall, a sample of n=36 freshmen was selected to participate in a new 4hour training program designed to improve study skills. To evaluate the effectiveness of the new program, the sample was compared with the rest of the freshman class. All freshmen must take the same English language skills course, and the mean score on the final exam for the entire freshman class was μ = 74. The students in the new program had a mean score of M=79.4 with a standard deviation of s= 18.
a. On the basis of these data, can the college conclude that the students in the new program performed significantly better than the rest of the freshman class? Use a one-tailed test with α = .05
b. Can the college conclude that the students in the new program are significantly different from the rest of the freshman class? Use a two-tailed test with α = .05
2. 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 infant could feed. 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 was 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 preferences between the two, you would expect the time to be divided evenly, with an average of μ =3 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= 9 infant monkeys average M= 15.3 hours per day with SS=216 with the terry cloth mother. Is this result sufficient to conclude that the monkeys spent significantly more time with the softer mother than would be expected if there were no preference? Use a two tailed test with α = .05
3. A researcher would like to examine the effects of humidity on eating behavior. It is known that laboratory rats normally eat an average of μ = 21 grams of food each day. The researcher selects a random sample of n= 16 rats and places them in a controlled atmosphere room in which the relative humidity is maintained at 90%. The daily food consumption scores for the rats are as follows:
14, 18, 21, 15, 18, 18 , 21, 18, 16, 20, 17, 19, 20, 17, 17, 19
a. Can the researcher conclude that humidity has a significant effect on eating behavior? Use a two-tailed test with
α = .05
b. Compute the estimated d and r^2 to measure the size of the treatment effect.
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