Discussion:
Q1: A personnel psychologist studying adjustment to the job of new employees found that employees' amount of education (in number of years) predicts ratings by job supervisors two months later. The regression constant in the linear prediction rule for predicting job ratings from education is 0.5 and the regression coefficient is .40. (a) Indicate the predictor variable, and (b) the criterionvariable. (c) Write the linear prediction rule for this example. Indicate the predicted job rating for employees with each of the following amount of education
(in years): (d) 8, (e) 10, (f) 17, (g) 19, and (h) 21.
Q2: A clinical psychologist has found that scores on a new depression scale predict satisfaction with psychotherapy. The regression constant in the linear prediction rule for predicting satisfaction from the depression score is 12 and the regression coefficient is .4. (a) Indicate the predictor variable, and (b) the criterion variable. (c) Write the linear prediction rule for this example. Indicate the predicted satisfaction for people with each of the following depression scores: (d) 8, (e) 6, (f) 5, (g) 3, and (h) 0.
Q3: Evolutionary theories often emphasize that humans have adapted to their physical environment. One such theory hypothesizes that people should spontaneously follow a 24-hour cycle of sleeping and waking-even if they are not exposed to the usual pattern of sunlight. To test this notion, eight paid volunteers were placed (individually) in a room in which there was no light from the outside and no clocks or other indications of time. They could turn the lights on and off as they wished. After a month in the room, each individual tended to develop a steady cycle. Their cycles at the end of the study were as follows: 25, 27, 25, 23, 24, 25, 26, and 25.
Q4: Using the 5% level of significance, what should we conclude about the theory that 24 hours is the natural cycle? (That is, does the average cycle length under these conditions differ significantly from 24 hours?) (a) Use the steps of hypothesis testing. (b) Sketch the distributions involved. (c) Explain your answer to someone who has never taken a course in statistics.
Q5: Do students at various colleges differ in how sociable they are? Twenty-five students were randomly selected from each of three colleges in a particular region and were asked to report on the amount of time they spent socializing each day with other students. The results for College X was a mean of 5 hours and an estimated population variance of 2 hours; for College Y, M = 4, S2 = 1.5; and for College Z, M = 6, S2 = 2.5. What should you conclude? Use the .05 level. (a) Use the steps of hypothesis testing, (b) figure the effect size for the study; and (c) explain your answers to (a) and (b) to someone who has never had a course in statistics.