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4. Explain why t distribution tends to be flatter and more spread than the normal distribution.

12. Last fall, a sample of n = 36 freshmen was selected to participate in a new 4-hour training program designed to improve study skills. To evaluate the effectiveness of the new program, the sample was compared with the rest of the freshmen class. All freshmen must take the same English Languages Skills course, and the mean score on the final exam for the entire freshmen class was µ =74. The students in the new program has 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 freshmen class? Use a one-tailed test with ± = .05.

b. Can the college conclude that the students in the new program are significantly different from the rest of freshmen class? Use a two-tailed test with ± = .05.

16. In a classic study of infant attachment, Harlow (1959) placed infant monkeys in cages with two artificial surrogate mother. One â??mother was made from bare wire mesh and contained a baby bottle which the bottle from infants could feed. He other mother was made from soft terry cloth and did not provide any access to food. Harlow observed the infants and recorded how much time per day was spent with each mother. In a typical day, the infant 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 of µ =9 hours for each of the mothers. However, the typical hours monkey spent around 15 hours per day with the terry cloth mother, indicating a strong preference for the soft, cuddly mother. Suppose a sample on n = 9 infant monkeys averaged M = 15.3 hours per day with SS = 216 with the terry 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 ± =.05.

22. 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= 21grams of food each day. He researcher selects a random of n =16 and places them in controlled atmosphere room in which the relative humidity is maintained at 90%. The daily food consumption scores for the rats are as follows:

a. Can the researcher conclude that humidity has a significant effect on eating behavior? Use a two-tailed test with ± =.05.

b. Compute the estimated d and r2 to measure the size of the treatment effect.

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