In addition to monitoring weight gain, food consumed, and activity level, the study measured stress levels in the mice by measuring corticosterone levels in the blood (higher levels indicate more stress). Conditions for ANOVA are met and computer output for corticosterone levels for each of the three light conditions is shown.

(a) What is the conclusion of the analysis of variance test?
(b) One group of mice in the sample appears to have very different corticosterone levels than the other two. Which group is different? What aspect of the data explains why the ANOVA test does not find this difference significant? How is this aspect reflected in both the summary statistics and the ANOVA table?

Studies have shown that exposure to light at night is harmful to human health. Data A.1 on page 136 introduces a study in mice showing that even low-level light at night can interfere with normal eating and sleeping cycles and can have an effect on weight gain and glucose intolerance. In the study, mice were randomly assigned to live in one of three light conditions: LD had a standard light/dark cycle, LL had bright light all the time, and DM had dim light when there normally would have been darkness.

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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Level N Mean StDev DM 10 73.40 67.49 LD 70.02 54.15 LL 50.83 42.22 One-way ANOVA: Corticosterone versus Light Source Light DF MS 2 2713 1357 0.43 0.656 Error 75782 3158 24 Total 26 78495