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Re: Test Failure

From: Ben Pfaff
Subject: Re: Test Failure
Date: Sun, 16 Apr 2006 22:04:23 -0700
User-agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux)

John Darrington <address@hidden> writes:

> I'm not sure what all the columns mean in
> tests/expressions/randist/chisq.out.  Can we add an explanation somewhere?

It'd certainly be a good idea.  It's all generated by a script,
so the script could be modified to add the explanations.

> Is the 5th column the probability? If so, then my book of tables tells
> me that Chi-Squared for 2 degrees of freedom and p = 0.01 is indeed
> 9.21, in which case the test is wrong, and for some reason my machine
> is the only one computing the value correctly.

In this particular table:
    x is computed from P and df.
    sig is computed from x and df.
Thus, if something's wrong it's the sig value that's wrong, not
the x.

The columns for the chisq output are, from left to right, P, df,
x, CDF, PDF, and significance.

       P       df        x      CDF      PDF      sig
     .99     2.00     9.21      .99      .00      .01 

Here's the actual code that prints the table:
    COMPUTE x = IDF.chisq (P, df).
    COMPUTE cdf = cdf.chisq (x, df).
    COMPUTE pdf = pdf.chisq (x, df).
    COMPUTE sig = sig.chisq (x, df).
    PRINT OUTFILE='chisq.out'/P df x cdf pdf sig.
    0.99 2

> Maybe Jason would like to comment on this.

He's much more knowledgeable on this topic than I ever will be.
Ben Pfaff 
email: address@hidden

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