The developers plan a study in a sleep lab to test their theory. The test group will use their app and the control group will just go to sleep without it. (A real study might have a slightly more complicated design, but this simple design will let us better explain the statistical models.) The statistical setup behind most experiments (including this one) starts with a hypothesis that there is no difference between the groups, called the null hypothesis. If the developers collect sufficient evidence to reject this hypothesis, then they will conclude that their app really does help people fall
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