Question

In Data 4.1 on page 258, we examine a study in which mice were randomly assigned to either a normal light/dark cycle or to have a light on around the clock. According to the paper describing that study, "The global increase in the prevalence of obesity and metabolic disorders coincides with the increase of exposure to light at night." The study is examining whether light at night plays a causal role in the obesity epidemic. In Data 4.1, we examine the effect of the different light conditions on body mass gain after three weeks. In fact, the actual experiment lasted 8 weeks and examined many additional variables. The data referenced here are available in LightatNight8weeks. Some of the variables are summarized in the following table. Variable Name Variable Description Condition Treatment group (Light or Dark) BMGain Change in body mass (in grams) after 8 weeks Corticosterone Blood corticosterone level (a measure of stress) DayPct Percentage of calories consumed during the day Consumption Average daily food consumption (in grams) GlucoseInt Glucose intolerant at end of study? (Yes or No) Activity A measure of physical activity level Higher blood corticosterone levels indicate greater physiological levels of stress. Find and interpret a 90% confidence interval for the difference in mean corticosterone levels between mice with a light on and mice in darkness. Does the confidence interval allow us to conclude that there is a difference in mean corticosterone levels between the two groups? If so, which group has higher mean levels?

In Data 4.1 on page 258, we examine a study in which mice were randomly assigned to either a normal light/dark cycle or to have a light on around the clock. According to the paper describing that study, "The global increase in the prevalence of obesity and metabolic disorders coincides with the increase of exposure to light at night." The study is examining whether light at night plays a causal role in the obesity epidemic. In Data 4.1, we examine the effect of the different light conditions on body mass gain after three weeks. In fact, the actual experiment lasted 8 weeks and examined many additional variables. The data referenced here are available in LightatNight8weeks. Some of the variables are summarized in the following table.

Variable Name
Variable Description
Condition
Treatment group (Light or Dark)
BMGain
Change in body mass (in grams) after 8 weeks
Corticosterone
Blood corticosterone level (a measure of stress)
DayPct
Percentage of calories consumed during the day
Consumption
Average daily food consumption (in grams)
GlucoseInt
Glucose intolerant at end of study? (Yes or No)
Activity
A measure of physical activity level

Higher blood corticosterone levels indicate greater physiological levels of stress. Find and interpret a 90% confidence interval for the difference in mean corticosterone levels between mice with a light on and mice in darkness. Does the confidence interval allow us to conclude that there is a difference in mean corticosterone levels between the two groups? If so, which group has higher mean levels?

Added by Salvador W.

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