A study was done on female mice to see whether the amount of light affects the risk of develop ing tumors. Fifty mice were randomly assigned to a regimen of 12 hours of light and 12 hours of dark (LD). Fifty similar mice were assigned to 24 hours of light (LL). The study began when the mice were 2 months old. The mice were observed for about two years. Four of the LD mice developed tumors, and 15 of the LL mice developed tumors.
a. What percentage of the LD mice in the sample developed tumors? And what percentage of the LL mice developed tumors? Compare these percentages and comment.
b. Create a two-way table showing the observed values. Label the columns (across the top) with LD and LL.
c. Test the hypothesis that the amount of light is associated with tumors (at the 0.05 level of significance).
d. Some researchers are now starting to investigate whether this phenomenon occurs in humans. They are concerned about shift workers- workers (such as nurses) who may have night shifts. Why would this be a concern?