Chapter 12: Misconceptions

When people read, hear, or prepare research summaries, they sometimes have misconceptions about what is or isn't "sound practice" regarding the collection, analysis, and interpretation of data. Here are some of these common (and dangerous) misconceptions associated with the content of Chapter 12.

  1. The Fisher, Duncan, Newman-Keuls, Tukey, and Scheffé test procedures produce valid result only if they are used in post hoc investigation.
  2. If the omnibus F from a one-way ANOVA turns out to be significant, at least one of the pairwise comparisons in the post hoc investigation will definitely turn out significant.
  3. If pairwise comparisons (either planned or post hoc) reveal that Group A is not significantly different from Group B and that Group B is not significantly different from Group C, then it will also be the case that Group A is not significantly different from Group C.
  4. Dunnett's test should be used only if one of the groups in the study is either a true control group or a placebo group.
  5. Pairwise comparisons can legitimately be conducted only if the ANOVA's omnibus F has first turned out to be significant.
  6. In deciding which specific test procedure to use for making pairwise comparisons, the typical researcher weighs the risks associated with procedures that are overly liberal vs. the risks associated with procedures that are overly conservative.
  7. Scheffé's procedure is good for making pairwise comparisons in a post hoc investigation.
  8. Planned and post hoc comparisons cannot logically be used together in the same study.

Copyright © 2012

Schuyler W. Huck
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