• Type: Sub-task
    • Status: Closed
    • Priority: Major
    • Resolution: Duplicate
    • Affects Version/s: None
    • Fix Version/s: ODF 1.2
    • Component/s: OpenFormula
    • Labels:


      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)
      > 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.]




            • Assignee:
              aguelzow Andreas Guelzow
              rcweir Robert Weir (Inactive)
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