https://bugs.freedesktop.org/show_bug.cgi?id=86284
Bug ID: 86284
Summary: t-test wrongly hypothesizes mean difference when using
the statistics assistant
Product: LibreOffice
Version: 4.3.3.2 release
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: major
Priority: medium
Component: Spreadsheet
Assignee: [email protected]
Reporter: [email protected]
Created attachment 109462
--> https://bugs.freedesktop.org/attachment.cgi?id=109462&action=edit
Sample Spreadsheet showing the test
Summary:
When using the Data->Statistics->t-test menu, one can get a dialog box to
auto-generate a paired t-test.
By default, the test is done with the hypothesis that the mean difference is 2
(always the number two), while in almost every case everybody wants to test the
hypothesis of equal means (difference zero).
Once the table is generated, it's easy to work around this bug, by storing 0 in
the cell "Hypothesized Mean Difference" (by default, it's 2).
But, it's very misleading. The hypothesized mean difference is not shown in the
dialog box, and the generated "hypothesized mean difference" cell is hidden in
many cells of various statistics.
Steps to reproduce:
Create two columns of numbers.
Select the data.
Go to Data->Statistics->t-test
Select an output cell
Click OK
Observed behavior:
The p-value of the test is computed based on the null hypothesis : mean((column
A)-(column B)) = 2
Expected behavior:
The p-value of the test is computed based on the null hypothesis : mean((column
A)-(column B)) = 0
Bugfix:
In file sc/source/ui/StatisticsDialogs/TTestDialog.cxx
b/sc/source/ui/StatisticsDialogs/TTestDialog.cxx
Replace the two lines:
aOutput.writeValue(2);
aTemplate.autoReplaceAddress("%HYPOTHESIZED_MEAN_DIFFERENCE%",
aOutput.current());
With:
aOutput.writeValue(0);
aTemplate.autoReplaceAddress("%HYPOTHESIZED_MEAN_DIFFERENCE%",
aOutput.current());
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