LIGHT AT NIGHT MAKES FAT MICE

Studies have shown that exposure to light at night is harmful to human health. A study in mice shows that light at night has an effect on weight gain after just three weeks. 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.

Body Mass Gain

The mice in the study had body mass measured throughout the study. Computer output showing an analysis of variance table to test for a difference in mean body mass gain (in grams) after four weeks between mice in the three different light conditions is shown below. The conditions for ANOVA are met. The null hypothesis is that the amount of light at night does not affect how much weight is gained. The alternative hypothesis is that the amount of light at night has some effect on mean weight gain.

Level N Mean StDev

DM 10 7.859 3.009

LD 8 5.926 1.899

LL 9 11.010 2.624

One-way ANOVA: BM Gain versus Light

Source DF SS MS F P

Light 2 113.08 56.54 8.38 0.002

Error 24 161.84 6.74

Total 26 274.92

(a)What is theF-statistic?

What is thep-value?