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The null hypothesis is the hypothesis that your control and experimental groups behave roughly the same* . This is the baseline assumption when group membershi
by evmar 11y ago
The null hypothesis is the hypothesis that your control and experimental groups behave roughly the same* . This is the baseline assumption when group membership is randomly assigned. It is not at all arbitrary.
* see my below comment for elaboration on what "same" means
- loup-vaillant 11y agoOkay, but, it's like expecting the two groups to be the same, which is a bit ridiculous. I'd rather just measure how much evidence the experiment provides either way.
- nonbel 11y agoExactly, we do not care they are different (usually). We care in what way and how much they are different. Then we care about what possible explanations there may be for that difference. I would say an exception is studies of ESP, etc where the existence of any effect would be surprising. However, in practice, everyone just assumes paranormal researchers messed up the experiment somehow. Small effects are not taken seriously even if they are "significant" because there are many explanations for such differences.
- loup-vaillant 11y ago> I would say an exception is studies of ESP Actually, E.T. Jaynes touched that topic a bit, and argued that it's not really an exception: probability theory applies to this phenomenons (or lack thereof) as usual. If I recall correctly, he reached the same conclusion as you just did: if a study looks like it demonstrated an instance of ESP, it probably went wrong.
- nonbel 11y agoCheck out this paper: http://arxiv.org/abs/1311.0081 http://arxiv.org/abs/1311.0081 Your interpretation is fine up until we start using a cutoff and talking about significant or not significant results, whether the null hypothesis is true, etc. It is using significance levels that introduces the nonsense.