Thanks Felipe.
I think we must describe what the software currently does in the Calc
Guide - enhancements can be requested via Bugzilla but they may or may
not happen depending on volunteer effort.
In summary, it appears that we need to update the description in Chapter
9 (and maybe the Help) as follows:
Include a statement that normally, if the sample size is not large (n <
30), the Paired t-test tool may be more appropriate.
After selecting the tool, the user should enter the variances of the two
datasets into the fields provided. In the example given the user could
enter the formula =VAR(A1:A13) into cell E5 and the formula =VAR(B1:B13)
into cell F5. The subsequent z and P values will be updated
automatically.
The user can also update the required Alpha (cell E2) and Hypothesised
Mean Difference (cell E3) values. Again, the subsequent z and P values
will be updated automatically.
State that the user should compare the selected Alpha level to the
appropriate calculated P value (depending whether a one-tailed or a
two-tailed test is required). If the calculated P value is smaller than
the Alpha level, then the user should reject the hypothesis (which, in
the example given, is that the means of the two data sets are the same).
Update the figure accordingly.
Does that make sense?
Regards,
Steve
------ Original Message ------
From: "Felipe Viggiano" <[email protected]>
To: "Steve (GMail)" <[email protected]>
Cc: "Documentation Team" <[email protected]>
Sent: 04/09/2020 03:12:40
Subject: Re: Re[2]: [libreoffice-documentation] Calc's Z-test tool
Hello everyone,
About the matter, I'm currently reviewing the
CG7009-DataAnalysis-SF-12Aug2020, and got to the Z-test tool part.
After creating the results table, is possible to insert the variance in
their respective cells, but I was looking to the Z-test wiki page
referred in the chapter and it says this:
"If the population variance is unknown (and therefore has to be
estimated from the sample itself) and the sample size is not large (n <
30), the Student's t-test may be more appropriate."
I just did a little research on google and found this website doing
some explanation about Z-Test:
https://www.solver.com/z-test-two-sample-means
When running the example in Calc and manually inserting the variances
in the cells of the Z-Test results, the output was identical to the
example on the website.
So I'm guessing that LO Calc should be able to calculate the variance
from the given data, and this should be fixed in the software.
Or, maybe we can put a note to the user to insert the variances after
creating the table.
Best regards,
Felipe Viggiano
Em qua., 2 de set. de 2020 às 07:55, Steve (GMail)
<[email protected]> escreveu:
Thanks Ilmari and Mark,
I'm happy to update the section in the 7.0 Calc Guide (which is
currently in preparation) but I'm still confused. Why does the z-test
tool think that the variance of the given data sets is zero? As you
say
Ilmari, that is not a number that the user currently enters.
Regards,
Steve
------ Original Message ------
From: "Ilmari Lauhakangas" <[email protected]>
To: [email protected]
Sent: 02/09/2020 11:40:06
Subject: Re: [libreoffice-documentation] Calc's Z-test tool
>Thanks! That was my gut feeling.
>
>So the immediate action would be to change the screenshots in Help
and Calc guide so the variance cells have non-zero values, also adding
a note to the instructions.
>
>A further question is, should we consider adding fields for inputting
variance values into the Z-test tool itself? Looking at Microsoft
Office docs, Excel has these. This would become an enhancement request
in Bugzilla.
>
>Ilmari
>
>Mark Morin kirjoitti 2.9.2020 klo 2.57:
>>Variance can't be zero for analysis of variance tests (t test, F
test,
>>etc). Statistical testing assumes that you have variance otherwise
you
>>really wouldn't need a test.
>>
>>On 9/1/2020 4:48 PM, Ilmari Lauhakangas wrote:
>>>I was looking at a bug report again:
>>>https://bugs.documentfoundation.org/show_bug.cgi?id=132983
>>>
>>>The reporter is scratching their head over the "division by zero"
>>>result for z.
>>>
>>> From what I can see, the "Known variance" values can't both be
zero,
>>>if you want to avoid the #DIV/0! results. You have to give at least
>>>one of them a positive non-zero value.
>>>
>>>Now, looking at Help:
>>>https://help.libreoffice.org/7.1/en-US/text/scalc/01/statistics_test_z.html
>>>
>>>
>>>and the Calc guide chapter CG7009-DataAnalysis-SF-12Aug2020, we see
>>>this same "division by zero" result and the reader is left holding
it.
>>>
>>>How to present this better in the docs? I have no experience on the
>>>topic, but I hope we can find some statistician to shed light on
this!
>>>
>>>Ilmari
>>>
>>
>
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