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Dependent Samples T-test

Dependent Samples T-test

The dependent samples t-test is used to compare the sample means from two related groups.  This means that the scores for both groups being compared come from the same people. The purpose of this test is to determine if there is a change from one measurement (group) to the other.

Basic Hypotheses

Null: The mean difference between the two groups is not different from 0.
Alternative: The mean difference between the two groups is different from 0.

Real-World Examples
  • Pre-test/Post-test
    • Is there an improvement in reading scores after participating in the Read Like a Pro course?
    • Do people recall more words after learning a memorization strategy?
  • Comparing different treatments
    • Do people perform better when given praise or punishment?
    • Is there a difference in how many miles a car can be driven when using AC versus having the windows down?

Reporting Results in APA Style

When reporting the results of the dependent-samples t-test, APA Style has very specific requirements on what information should be included. Below is the key information required for reporting the results of the. You want to replace the red text with the appropriate values from your output.

t(degrees of freedom) = the t statistic, p = p value.

Example:
A dependent-samples t-test was run to determine if long-term recall improved with the introduction of the Say it Again memorization technique. The results showed that the average number of words recalled without this technique (M = 13.5, SD = 2.4) was significantly less than the average number of words recalled with this technique (M = 16.2, SD = 2.7), (t(52) = 4.8, p < .001).
 

Notes:
  • When reporting the p-value, there are two ways to approach it. One is when the results are not significant. In that case, you want to report the p-value exactly: p = .24. The other is when the results are significant. In this case, you can report the p-value as being less than the level of significance: p < .05.
  • The t statistic should be reported to two decimal places without a 0 before the decimal point: .36
  • Degrees of freedom for this test are n - 1, where "n" represents the number of pairs in the sample. n can be found in the SPSS output.
     
Additional Resources

Laerd Statistics - Dependent T-test for Paired Samples guide
Statistics Solutions - Paired Samples T-test

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