Microsoft KB Archive/117362

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Excel: Incorrect F-Test F Critical One-Tail Value Returned

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The information in this article applies to:


 * Microsoft Excel for Windows, versions 4.0, 4.0a

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SYMPTOMS
In Microsoft Excel, when you use the F-Test: Two-Sample For Variances tool in the Analysis ToolPak to compare two data ranges, the F Critical one-tail result that is returned is incorrect.

CAUSE
This error occurs when the variance in the second range is greater than the variance in the first range. In this case, the F-Critical One-Tail value returned is for that of alpha*2. The value should be for that of 1-alpha. The F-Test: Two-Sample For Variances tool uses 0.5 as the value of alpha.

For example, if you use the F-Test: Two Sample For Variances tool to perform a two-sample F-test using the following ranges of data:

A1: 1 B1: 1

A2: 2 B2: 2

A3: 3 B3: 3

A4: 3 B4: 4 The variance in the range B1:B4 is greater than in A1:A4. If you use the range A1:A4 as the variable one input range, the F Critical One-Tail value returned is 5.390774. This matches the F distribution tables for alpha=.10 (alpha*2), instead of the correct value of .107798 (F distribution tables for alpha=.95 (1-alpha)).

STATUS
Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. This problem has been corrected in Microsoft Excel version 5.0.

MORE INFORMATION
The F-Test: Two-Sample for Variances tool is available in the Analysis Tools dialog box by choosing Analysis Tools from the Options menu when the Analysis ToolPak add-in (ANALYSIS.XLA) is loaded.