A Randomized Controlled Study of Chronically Sleep-Deprived (<6

A randomized controlled study of chronically sleep-deprived (<6.5 hr per night) , morbidly obese subjects examined whether sleep extension is associated with weight loss and metabolic and endocrinal improvements.  The intervention consisted of education regarding sleep hygiene and a gradual change to subjects' bedtimes to earlier in the evening.  Participants underwent general screening at visit 1 with collection of baseline parameters; then, 2 months later, at visit 2, subjects were randomized into either an intervention group or a comparison group.  Researchers evaluated several parameters, including sleep duration, sleepiness, and sleep quality.  The following results were reported: Note: Data is reported as mean ± standard deviation.
^*p < 0.05.
¹ ESS (Epworth Sleepiness Scale [daytime sleepiness]) >10 = sleepy.
² PSQI (Pittsburgh Sleep Quality Index [subjective sleep quality]) >5 = abnormal.
There were statistically significant differences in all 3 parameters between visit 1 and visit 2.  Which of the following is the best explanation for the difference between findings at the screening and randomization visits?

A) Allocation bias
B) Confounding bias
C) Hawthorne effect
D) Placebo effect
E) Selection bias

Correct Answer:

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