[OASIS Issue Tracker] Created: (OFFICE-2311) ZTEST

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ZTEST
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                 Key: OFFICE-2311
                 URL: http://tools.oasis-open.org/issues/browse/OFFICE-2311
             Project: OASIS Open Document Format for Office Applications (OpenDocument) TC
          Issue Type: Sub-task
          Components: OpenFormula
    Affects Versions: ODF 1.2
            Reporter: Robert Weir 


5.) ZTEST
> TODO: OOo Calc and Gnumeric produce the same results. Excel (2007 
> beta) claims to calculate the one-tailed test.
> All produce different results than expected! What OOo Calc and 
> Gnumeric calculate is out of my scope. Excel tries to calculate the 
> probability by integrating from minus infinity to z and substracts 
> this from one. That would only be right, if the absolute value of z is 
> taken, not the signed z! (I speak already of the one-tailed results 
> for this case, so no confusion here.)
> So, either I made a mistake/misinterpretation or all three apps don't 
> get it right(TM)

Well, I'll test it in R. There is NO standard z-test, BUT the t-test 
will do it, too. [There is also the package 'TeachingDemos' wich does 
define the z-test]

> > z.test(x, mu=15, sd=sd(x))
>
>         One Sample z-test
>
> data:  x
> z = 0.3111, n = 30.000, Std. Dev. = 8.803, Std. Dev. of the sample mean
> = 1.607, p-value = 0.7557
> alternative hypothesis: true mean is not equal to 15
> 95 percent confidence interval:
>  12.34980 18.65020
> sample estimates:
> mean of x
>      15.5
where x = 1..30

This same example gives a value of 0.38 in Calc. I have NO idea what 
0.38 stands for. And I just noticed that it is impossible to compute a 
t-test on a single array in Calc against the expected mean - or did I 
miss something?
[The t-test in R gives virtually identical results, because a sample 
size of 30 is large enough to approximate the z-distribution.]


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