Post hoc tests

Definition

Post hoc tests are statistical analyses conducted after an initial analysis (like ANOVA) to explore which specific group means are different when the overall results are significant. They help in determining the exact nature of the differences between groups, especially in complex designs with multiple groups or factors, providing clarity on main effects and interactions.

5 Must Know Facts For Your Next Test

1. Post hoc tests are only conducted after finding a significant F-statistic in ANOVA, indicating that at least one group mean is different.
2. Common post hoc tests include Tukey's HSD, Bonferroni, and Scheffé, each with different methods for controlling Type I error rates.
3. These tests adjust for multiple comparisons, helping to prevent false positives when testing for differences across multiple groups.
4. Post hoc tests can be used not only in ANOVA but also in more complex models like Two-Way ANOVA and ANCOVA, aiding in understanding interactions and main effects.
5. Choosing the appropriate post hoc test depends on the study design, sample size, and number of comparisons being made.

Review Questions

• How do post hoc tests enhance the interpretation of results from ANOVA?
  • Post hoc tests enhance interpretation by specifying which group means differ when ANOVA reveals a significant F-statistic. While ANOVA tells us that at least one mean is different, it doesn't indicate where those differences lie. By applying post hoc tests like Tukey's HSD or Bonferroni after finding significance, researchers can pinpoint exact group comparisons that contribute to overall variance, leading to clearer insights into main effects and potential interactions.
• In what scenarios would you choose to perform post hoc tests after conducting a Two-Way ANOVA rather than a One-Way ANOVA?
  • Post hoc tests after a Two-Way ANOVA are essential when there are two independent variables, and we need to explore how their interaction affects the dependent variable. If we find significant interaction effects, it becomes crucial to analyze simple main effects using post hoc tests. In contrast, a One-Way ANOVA would only require post hoc testing if there are three or more levels within a single factor. Thus, the decision hinges on the complexity of the design and the number of factors involved.
• Evaluate how post hoc tests can impact the reporting of results in an ANCOVA study.
  • Post hoc tests significantly influence how results are reported in an ANCOVA study by providing detailed comparisons among adjusted group means. When conducting ANCOVA, researchers control for covariates which can alter mean comparisons; therefore, post hoc tests help clarify which groups still differ after adjustments. Reporting these findings adds rigor and transparency to the results, allowing readers to understand not just that differences exist but where they lie—an important aspect when discussing implications and potential applications of findings.

Related terms

ANOVA: Analysis of Variance (ANOVA) is a statistical method used to compare the means of three or more groups to understand if at least one group mean is significantly different from the others.

Main Effects: Main effects refer to the direct influence of an independent variable on a dependent variable, measured in the context of factorial designs or ANOVA.

Interaction Effects: Interaction effects occur when the effect of one independent variable on a dependent variable changes depending on the level of another independent variable.