Threats to Internal Validity
Null Hypothesis
What the Null Hypothesis Let’s use a simple example. How Does a Blind Man Know It’s Raining? Imagine a blind man walking outside. He can’t see a thing in front of him and can only rely on his sense of smell and touch. While he’s walking outside, he starts to feel water droplets on his head. He thinks it might be raining, but he can’t say for sure because he can’t actually see the rain coming down from the sky. In frequentist statistics, the hypothesis that says “it’s raining” is the alternative. The hypothesis that says there’s “there’s no rain” is the null hypothesis. The null hypothesis generally assumes that there’s normality (i.e., no rain). Since the blind man can’t actually prove that there’s rain (from his lack of vision), he has to find evidence against the idea that there’s no rain. That’s what statisticians do when they employ frequentist methods. They’re blind people who can’t actually prove that it’s raining. Instead, they provide evidence that whatever is hap...
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