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Modified t-Test Procedures
To safely conduct post hoc comparisons without inflating the risk of making a Type I error, researchers use modified -test procedures rather than standard -tests. Techniques such as the Bonferroni procedure, Fisher's least significant difference (LSD) test, and Tukey's honestly significant difference (HSD) test are designed specifically for this purpose. While their mathematical details differ, their shared goal is to keep the overall risk of mistakenly rejecting a true null hypothesis at an acceptable level (typically close to ) across multiple comparisons.
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Research Methods in Psychology - 4th American Edition @ KPU
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Modified t-Test Procedures
What is the primary statistical problem that arises when conducting multiple independent-samples t-tests to compare every pair of group means in an experiment?
A researcher conducts six separate t-tests to compare every pair of means among four experimental groups, using an alpha level of .05 for each test. Because each individual test maintains only a 5% chance of a Type I error, the overall probability of making at least one Type I error across all six tests also remains at 5%.
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Bonferroni Procedure
Fisher's Least Significant Difference (LSD) Test
Tukey's Honestly Significant Difference (HSD) Test
Why do researchers use modified t-test procedures, such as the Bonferroni procedure or Tukey's honestly significant difference (HSD) test, rather than standard t-tests when conducting post hoc comparisons?
If a researcher decides to use standard t-tests rather than modified t-test procedures for multiple post hoc comparisons, they will successfully keep their overall risk of mistakenly rejecting a true null hypothesis at an acceptable level.