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>"For example, consider the ‘null’ hypothesis that the new drug has exactly the same effectiveness as the old drug." I'd encourage people to ask: Why should I

• andrewflnr 11y ago
  A strawman argument is a distorted version of someone else's position, formulated to be easy to knock down for the purpose of appearing to win debates. A null hypothesis is just a starting point for reasoning.
  • nonbel 11y ago
    And whose position is it that a drug/treatment/whatever has exactly zero effect? Also that there are exactly zero differences between two or more groups at baseline and this continues to be true for the duration of the study (except if due to the treatment)? Really, who is advocating that hypothesis? Also, a null hypothesis was originally the hypothesis to be nullified. There may be confusion due to the use of "null" here. Null != nil
    • evmar 11y ago
      From your comment history you appear to have some background in statistics, but what you're written here is curiously missing the fundamentals. It's not exactly clear what you're arguing, but I am definitely curious because I must be missing it! To answer your last question directly: nobody argues that there are zero differences between groups in an experiment, but rather that the central limit theorem applies, which is a statement about the distribution of means in particular circumstances. https://en.wikipedia.org/wiki/Central_limit_theorem https://en.wikipedia.org/wiki/Central_limit_theorem
      • nonbel 11y ago
        >"nobody argues that there are zero differences between groups in an experiment" The null hypothesis (usually) assumes that the two groups are samples from the same distribution. Do you agree?
        • evmar 11y ago
          Yes. Isn't that fundamental to experimental design, that group membership is random? (You certainly know this as well, so I'm again confused about what your question is intended to provoke.)
          • nonbel 11y ago
            And so what? Forget the math, say the two groups come from different distributions. Omniscient Jones told us so. What can we learn from that?
  • loup-vaillant 11y ago
    Interesting: how do you chose that starting point in the first place? Sounds like the null hypothesis is just as arbitrary than any Bayesian "prior" (prior probability distribution, I mean).
    • 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 ago
        Okay, 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 ago
          Exactly, 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 ago
  Let us see what Ronald Fisher said towards the end of his life regarding confusion over the null hypothesis: "We are quite in danger of sending highly trained and highly intelligent young men out into the world with tables of erroneous numbers under their arms, and with a dense fog in the place where their brains ought to be. In this century, of course, they will be working on guided missiles and advising the medical profession on the control of disease, and there is no limit to the extent to which they could impede every sort of national effort." Fisher, R N (1958). "The Nature of Probability". Centennial Review 2: 261–274 That is you downvoters.
• Confusion 11y ago
  Because any other null hypothesis has the same problem, but at least this one isn't biased.