Infants, even newborns, prefer to look at attractive faces compared to less attractive faces (Slater, et al., 1998). In the study, infants from 1 to 6 days old were shown two photographs of women’s faces. Previously, a group of adults had rated one of the faces as significantly more attractive than the other. The babies were positioned in front of a screen on which the photographs were presented. The pair of faces remained on the screen until the baby accumulated a total of 20 seconds of looking at one or the other. The number of seconds looking at the attractive face was recorded for each infant. Suppose that the study used a sample of n 5 9 infants and the data produced an average of M 5 13 seconds for the attractive face with SS 5 72.

If there were no preference, the 20 seconds should be divided equally between the two photographs. Note that all the available information comes from the sample. Specifically, we do not know the population mean or the population standard deviation. State the null hypothesis and use a two-tailed test with a 5 .05 to evaluate the hypothesis.