We have seen that light at night increases weight gain in mice and increases the percent of

Question:

We have seen that light at night increases weight gain in mice and increases the percent of calories consumed when mice are normally sleeping. What effect does light at night have on glucose tolerance? After four weeks in the experimental light conditions, mice were given a glucose tolerance test (GTT). Glucose levels were measured 15 minutes and 120 minutes after an injection of glucose. In healthy mice, glucose levels are high at the 15-minute mark and then return to normal by the 120-minute mark. If a mouse is glucose intolerant, levels tend to stay high much longer. Computer output is shown giving the summary statistics for both measurements under each of the three light conditions.

Descriptive Statistics: GTT-15 Light N Mean Variable StDev GTT-15 DM 10 338.8 80.6 LD 318.7 106.5 LL 373.6 59.1 Descript

(a) Why is it more appropriate to use a randomization test to compare means for the GTT-120 data?
(b) Describe how we might use the 27 data values in GTT-120 to create one randomization sample.

(c) Using a randomization test in both cases, we obtain a p-value of 0.402 for the GTT-15 data and a p-value of 0.015 for the GTT-120 data. Clearly state the results of the tests, using a 5% significance level. Does light at night appear to affect glucose intolerance?

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.

We have seen that light at night increases weight gain