10.3 Assignment Instructions

10.3.1 R Script

Produce the following in R:

  1. M and SD of stress at pre- and post-intervention for the whole sample and for each subgroup.
  2. Directional paired samples t test of the effect of the change in stress for the whole sample (i.e., not separately for each group). Include Cohen’s dz with its associated 95% CI.
  3. A column added to the data frame which shows each participant’s change in stress from pre- to post-intervention.
  4. A 2x2 ANOVA model as described in the analytic strategy.
  5. Estimated marginal means of each of the four conditions.
  6. Pairwise comparisons of stress between the four conditions.
  7. An interaction plot showing the mean of each of the four conditions.

10.3.2 Results

Write a results section, consistent with APA style that includes the following:

  • Results of the tests of the four hypotheses.
  • M and SD of stress at pre- and post-intervention for the whole sample and for each subgroup. These could be efficiently reported in a table.
  • The interaction plot.

10.3.3 Discussion Questions

Provide short answer responses to the following:

  • Provide a statement of support or non-support for each hypothesis.
  • The scale only included 5 response options. The authors provide justification for why this is; but it is still less than ideal. What problems might result from using such a brief measure?
  • This study was testing a specific intervention under four conditions. Based on the results of the study, would you recommend that the intervention be implemented? Under what conditions? Consider not only the results of the significance tests but the size of the effects. Also, consider the relative difficulty of implementing the intervention in each of the four conditions. The greater the difficulty of implementing an intervention, the stronger the evidence it requires.