Article ID: 829247  View products that this article applies to. On This PageSUMMARYThis article describes the misleading labels that exist in
the output of each of the three Analysis ToolPak tTest tools, and that are common
to the output of all three tools. The reader must also be aware of the fact that the tTest: Paired Two Sample for Means tool can give incorrect results. For additional information about the tTest: Paired Two Sample for Means tool, click the following article number to view the article in the Microsoft Knowledge Base: 829252
(http://support.microsoft.com/kb/829252/
)
Excel Statistical Functions: Analysis ToolPak tTest: Paired Two Sample For Means
Microsoft Excel 2004 for Macintosh informationThe statistical functions in Excel 2004 for Mac were updated by using the same algorithms that were used to update the statistical functions in Microsoft Office Excel 2003 and later versions of Excel. Any information in this article that describes how a function works or how a function was modified for Excel 2003 and later versions of Excel also applies to Excel 2004 for Mac.MORE INFORMATIONProblems with misleading labels are illustrated and
discussed in this article. Example of usageTo illustrate the tTest tools, create a blank Excel worksheet, copy the following table, and then select cell A1 in your blank Excel worksheet. Then, paste the entries so that the following table fills cells A1:C20 in your worksheet.Collapse this table
The focus of this article is to understand the information in rows 16 to 20. In each tool, a tStatistic value, t, is computed and shown as "t Stat" in the output tables. Depending on the data, this value, t, can be negative or nonnegative. If you assume equal underlying population means, and if t is less than 0, "P(T <= t) onetail" gives the probability that a value of the tStatistic would be observed that is more negative than t. If t is greater than or equal to 0, "P(T <= t) onetail" gives the probability that a value of the tStatistic would be observed that is more positive than t. Therefore, if the label is replaced with one that is more accurate, the label would be "P(T > t) one tail". "t Critical onetail" gives the cutoff value so that the probability that an observation from the tdistribution with df degrees of freedom is greater than or equal to "t Critical onetail" is Alpha. The default level of Alpha is 0.05 for each tool and this can be changed in the input dialog box. The value of t Critical onetail can also be found by using the TINV(2*Alpha, df) function in Excel. Because TINV gives the cutoff for a twotailed ttest, use 2*Alpha instead of Alpha. If the twotailed probability of a t value higher in absolute value than this cutoff is 0.10, the onetailed probability of a t value higher than this cutoff is 0.05 (as is the onetailed probability of a t value less than the negative of this cutoff). "P(T <= t) twotail" gives the probability that a value of the tstatistic would be observed that is larger in absolute value than t. Therefore, if the label is replaced with one that is more accurate, the label would be "P(T > t) two tail". "t Critical twotail" gives the cutoff value so that the probability of an observed tStatistic larger in absolute value than "t Critical twotail" is Alpha. The value of t Critical twotail can also be found by using the TINV(Alpha, df) function in Excel. PropertiesArticle ID: 829247  Last Review: January 17, 2007  Revision: 3.2
