Microsoft Office Tutorials and References
In Depth Information
Testing to the T
The Student t-distribution has nothing to do with students. The originator of
the method was not allowed to use his real name due to his employer’s rules.
Instead, he used the name Student.
Testing to the T
The TTEST function returns the probability that two samples come from
populations that have the same mean. For example, a comparison of the
salaries of accountants and professors in New York City is under way. Are the
salaries, overall (on average), the same for these two groups? Each group is a
separate population, but if the means are the same, then the average salaries
are the same.
Polling all the accountants and professors isn’t possible, so a sample of each
is taken. Twenty-five random members of each group divulge their salary
in the interest of the comparison. Figure 10-1 shows the salaries of the two
groups, as well as the results of the TTEST function.
Student t-testing is generally used when the sample size is 30 items or fewer.
Figure 10-1:
Comparing
salaries.
The TTEST function returns 10.6 percent (0.106437) based on how the
arguments to the function were entered. This percentage says there is a 10.6
percent probability that the mean of the underlying populations are the same.
Said another way, this is the likelihood that the mean of all accountant
salaries in New York City matches the mean of all professor salaries in New York
City. The formula in cell E8 is =TTEST(A2:A26,B2:B26,2,2).
 
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