In Case Study 1.1, Lee Salk did an experiment to see if hearing the sound of a human heartbeat would help infants gain weight during the first few days of life. By comparing weight gains for two sample groups of infants, he concluded that it did. One group listened to a heartbeat and the other did not.
a. What are the null and alternative hypotheses for this study?
b. Was this a one-sided test or a two-sided test? Explain.
c. What would a type 1 and type 2 error be for this study?
d. Given the conclusion made by Dr. Salk, explain which error he could possi bly have committed and which one he could not have committed.
e. Rather than simply knowing whether there was a difference in average weight gains for the two groups, what statistical technique would have provided additional information? The following information is for Exercises 23 and 24: In Original Source 17 (link provided on the companion website), “ Monkeys reject unequal pay,” the researchers found that female monkeys were less willing to participate in an exchange of a small token for a piece of cucumber if they noticed that another monkey got a better deal. In one part of the experiment, a condition called “effort control,” the monkey witnessed another monkey being given a grape without having to give up a token (or anything else) in return. The first monkey was then cued to perform as usual, giving up a small token in return for a piece of cucumber. The proportion of times the monkeys were willing to do so was recorded, and the results are shown in Figure 1 (page 297) of the report. This “effort control” con­dition was compared with the “equality condition” in which the first monkey was also required to exchange a token for cucumber. For this part of the study, the researchers reported, “ Despite the small number of subjects, the overall exchange tendency varied significantly . . . comparing effort controls with equality tests, P , 0.05” (p 298). (The symbol, means “less than.”)