Computer output showing body mass gain (in grams) for the mice after four weeks in each of the three light conditions is shown, along with the relevant ANOVA output. Which light conditions give significantly different mean body mass gain?

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. 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 Mean StDev DM 10 7.859 3.009 LD 5.987 1.786 LL 11.010 2.624 One-way ANOVA: BM4Gain versus Light Source DF MS Light 116.18 2 58.09 8.96 0.001 Error 25 162.10 6.48 Total 27 278.28