Late Night Eating It is well-known that lack of sleep impairs concentration and alertness, and this might be due partly to late night food consumption. A 2015 study took 44 people aged 21 to 50 and gave them unlimited access to food and drink during the day, but allowed them only 4 hours of sleep per night for three consecutive nights. On the fourth night, all participants again had to stay up until $4 \mathrm{am}$, but this time participants were randomized into two groups; one group was only given access to water from $10 \mathrm{pm}$ until their bedtime at $4 \mathrm{am}$ while the other group still had unlimited access to food and drink for all hours. The group forced to fast from $10 \mathrm{pm}$ on performed significantly better on tests of reaction time and had fewer attention lapses than the group with access to late night food.

(a) What are the explanatory and response variables?

(b) Is this an observational study or a randomized experiment?

(c) Can we conclude that eating late at night worsens some of the typical effects of sleep deprivation (reaction time and attention lapses)?

(d) Are there likely to be confounding variables? Why or why not?