How to Calculate T Value in Excel

Written by dan howard
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How to Calculate T Value in Excel
Researchers in most fields consider a T value of less than .05 statistically significant. (BananaStock/BananaStock/Getty Images)

The student's t-test is a statistical operation that calculates the probability that two arrays of data are statistically identical to one another. You can perform a student's t-test in Microsoft Excel using the TTEST function. In order to use the function, you must have two arrays that contain the same number of members, and you must determine the appropriate type of t-test for your data.

Skill level:
Moderately Easy

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  1. 1

    Determine the cell addresses for the two data arrays that you wish to compare with a student's t-test. If your data is housed in cells A and B, rows one through 15, then the addresses of your arrays are "A1:A15" and "B1:B15." Both arrays must have the same number of entries to complete the test.

  2. 2

    Determine whether you want to perform a one-tailed or two-tailed test. If you are testing a pre-existing hypothesis that one array is larger than the other, then use a one-tailed test; if you are simply comparing whether the means are the same or different, then use a two-tailed test.

  3. 3

    Determine the type of t-test that you should perform. The type of test that you choose must be specified within the Excel TTEST formula. You must perform a paired t-test if the values in the two columns are related, such as when you are comparing measurements at two points in time from a single subject. If you obtained your two data arrays from two different samples, such as comparing independent control and test groups, then you perform a two-sample t-test. If you have reason to assume that your two independent samples should display similar levels of variance, then perform a two-sample equal variance t-test; otherwise, perform a two-sample unequal variance t-test.

  4. 4

    Click an empty cell that you'd like to use to calculate the value of the t-test.

  5. 5

    Type the following in the cell:

    =TTEST(Array1, Array2, Tails, Test Type)

    Substitute the cell addresses of your two data arrays in place of "Array1" and "Array2." Substitute the number of distribution tails that you are comparing in place of "Tails." Substitute the code for your t-test type in place of "Test Type"; type in "1" for a paired t-test, "2" for a two-sample equal variance t-test, and "3" for a two-sample unequal variance t-test.

    For example, to perform a paired, two-tailed t-test on two 15-item arrays in columns A and B, type:

    =TTEST(A1:A15, B1:B15, 2, 1)

  6. 6

    Press "Enter" once you've typed the appropriate formula in for your data ranges and t-test type. The probability that your data arrays are not significantly different is returned in the formula cell.

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