Scientists interested in the effect of exercise on the duration of sleep conducted the following study: 180180180 overweight men were randomly assigned to two groups. One group was instructed to perform aerobic exercise for about an hour per day, and the other group was instructed to continue with their exercise-less routine. The sleep duration of each subject was measured at two points: before the randomization and 101010 weeks after it. Then, the scientists calculated the change in sleep duration for each subject, where a positive value means the duration increased, and a negative value means it decreased.
What type of a statistical study did the scientists use?
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(Choice A)
A
Sample study

(Choice B)
B
Experiment

(Choice C)
C
Observational study
The scientists found that the mean change in sleep duration of the group who exercised is 656565 minutes greater than the mean change of the group who didn’t. Based on some re-randomization simulations, they concluded that the result is significant and not due to the randomization of the groups.
What valid conclusion can be made from this result?
Mark the most suitable choice.
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(Choice A)
A
The result suggests a positive correlation between daily exercise and sleep duration among overweight men.

(Choice B)
B
The result suggests that people who exercise daily sleep better than people who don’t.

(Choice C)
C
The results suggest that adopting an exercise regime may increase sleep duration among overweight men.

(Choice D)
D
The result suggests a positive correlation between daily exercise and sleep duration.