Propeller Head Plaza

RE: statistics question

75.50.157.189

In Reply to: RE: statistics question posted by Jon Risch on July 08, 2009 at 23:19:20

Something you don't mention is the problem of Type II error. (The chance that we fail to reject the null hypothesis when it is false.)

Let p be the probability that a listener picks the right answer on a single trial. For a perfect test subject, p=1.0. For someone who's guessing, p=0.5. In reality, p is somewhere in-between. Maybe it's 0.9, maybe it's 0.7, maybe it's 0.6. Something that rather shocked me was that for p=0.6, you need a LOT of trials to minimize Type II error. On the order of 50 trials if your significance level is 5%.

This may be one reason few amateur cable tests have shown a positive result. In a long-term listening style of test, who has time to do 50 trials? If we are dealing with a small p, the differences are real, but it takes many trials to reach a 5% significance level.

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RE: statistics question - Jon Risch 13:55:58 07/09/09 (0)

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