7.142 Weight-loss programs. In a study of the effectiveness of weight-loss programs, 47 subjects who were at least 20% overweight took part in a group support program for 10 weeks. Private weighings determined each subject’s weight at the beginning of the program and six months after the program’s end. The matched pairs t test was used to assess the significance of the average weight loss. The paper reporting the study said, “The subjects lost a significant amount of weight over time, t(46) = 4.68, p < 0.01.’’ It is common to report the results of statistical tests in this abbreviated style.53
(a) Why was the matched pairs statistic appropriate?
(b) Explain to someone who knows no statistics but is interested in weight-loss programs what the practical conclusion is.
(c) The paper follows the tradition of reporting significance only at fixed levels such as α = 0.01. In fact, the results are more significant than “p < 0.01’’ suggests. What can you say about the P-value of the t test?