In article <[EMAIL PROTECTED]>, les <[EMAIL PROTECTED]> wrote:
>i have 327 data points and i plotted the histogram which >looks like poisson distribution. I want to test the hypothesis that >this distribution is significantly different from uniform and want to get >get some confidence level (say 0.95 ). I was thinking of chi square but >does'nt chi square assume normal distributed data? "chi square" is the name of a distribution, which is often used as the name of a test that uses that distribution. Unfortunately, there are several such tests. One of these is for the variance of a normal distribution, which doesn't apply to your situation. Another "chi square" test, however, is for the fit of discrete data to a known distribution. This would be appropriate for you. At least it would be appropriate if the hypothesis you describe is actually appropriate. I wonder about that, though. You say the data "looks like a poisson distribution". A poisson distribution has no upper limit. You say you want to test the null hypothesis that the data comes from a uniform distribution. Uniform over what set of values? There has to be an upper limit to a uniform distribution. If there is some known upper limit, then perhaps you should really be thinking of the data as "looking" like it comes from a binomial distribution. At that point, one might wonder whether the null hypothesis you should really be testing is that the data is binomial with p=1/2. (I'm assuming your data consists of 327 non-negative integers, since you mention a Poisson distribution.) In general, it's dangerous to ask advice of this nature without saying anything about your real problem. You may well get advice that sounds authoratative (and maybe is, in a narrow sense), which then encourages you to think you're doing the right thing, when actually you're totally confused. By the way, the usual way of expressing the result of a hypothesis test is a "p-value". By "confidence level", I can only assume you mean one minus this p-value. However, you shouldn't say that you "want to get some confidence level (say 0.95)". You do the test, and you get some p-value. Your wants don't come into it. It's not like finding a confidence interval, where you can choose the confidence level. Radford Neal ---------------------------------------------------------------------------- Radford M. Neal [EMAIL PROTECTED] Dept. of Statistics and Dept. of Computer Science [EMAIL PROTECTED] University of Toronto http://www.cs.utoronto.ca/~radford ---------------------------------------------------------------------------- . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
