Hi all,
David King schrieb:
[..]
Whatever :). Yours is certainly clearer, mine a bit faster.
I've attached a patch with your proposal to the issue.
But both ways would have
fSumSqr - fSum*fSum/rValCount
which might give similar problems like in issue 78250.
Yes - really should use the same algorithm as VAR, DVAR, STDEV
etc.
The real problem I see is, that a function, even corrected in
one of
this ways, does not follow the definition in ODF1.2. What to
do?
I don't think that ODFF (draft of 16May08) has the definitive
answer to this:
"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)."
We've gone back to basics and understand exactly what Excel does,
which is
admittedly daft, and is not what they say in their knowledge base
article
(revised Jan08) or Help. We can reproduce the results in R. It
all supports
what 'TM' says. We can document how to use the function sensibly,
even if
Excel's documentation is faulty.
I read in http://office.microsoft.com/en-us/excel/HP100625561033.aspx:
ZTEST is calculated as follows when sigma is not omitted:
ZTEST(array,µ0)=1-NORMSDIST((xquer-µ0)/(sigma/sqrt(n)))
or when sigma is omitted:
ZTEST(array,µ0)=1-NORMSDIST((xquer-µ0)/(s/sqrt(n)))
where xquer is the sample mean AVERAGE(array); s is the sample standard
deviation STDEV(array); and n is the number of observations in the
sample COUNT(array).
And so does Calc work.
So as far as I can see we've got the thing nailed... Do you
agree?
Yes.
I have a load of things to feed back to ODFF anyway; I'll just
add this to the
list.
I thing, that further work on ZTEST should be postponed, until the
specification in ODF1.2 is finished.
kind regards
Regina
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