In Data A.1 on page 136, we introduce a study in which mice are randomly separated into one group on a normal light dark cycle and one group with bright light on all the time. Although the mice ate the same amounts and exercised the same, the sample mice with the light at night gained more weight. We wish to determine whether there is evidence that mean weight gain for all mice (not just this sample) is higher in the presence of light at night. The body mass gain, in grams, after four weeks is shown (rounded to the nearest whole number) inTable 4.11.

(a) What are the null and alternative hypotheses?
(b) How can we create one randomization sample? Create one (using cards or some other physical simulation) and record the results of your simulated sample in a table similar to Table 4.11.

Data A, 1 on page 136

Numerous studies have shown that exposure to light at night is harmful to human health. A recent study in mice shows that even low-level light at night can interfere with normal eating and sleeping cycles. Furthermore, the study finds that food is especially fattening if consumed at the wrong time of day, at least in mice. In the study, 27 mice were randomly split into three groups. One group was on a normal light€“dark cycle (LD), one group had bright light on all the time (LL), and one group had light during the day and dim light at night (DM). The dim light was equivalent to having a television set on in a room. The mice in darkness ate most of their food during their active (nighttime) period, matching the behavior of mice in the wild. The mice in both dim light and bright light, however, consumed more than half of their food during the well-lit rest period, when most mice are sleeping. Although the data collected show that the three groups of mice ate approximately the same amount of food and had the same levels of physical activity, the mice exposed to light at night gained substantially more weight, ate a greater percent of calories during the day, and were more likely to be classified as glucose intolerant at the end of the study. An absence of darkness seems to be associated with fatter mice.

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Bright light (LL) Light/Dark (LD) 10 10 11 9 12 9 11 9 17 5 6 7 8 3 8 6 6 4