Problem set 7

Complete this task in teams of two or three students.

Submission information: please submit on ZoneCours

Look at the ANCOVA example; this should be helpful in completing the problem set.

We consider Experiment 3 of Stekelenburg et al. (2021); (download the paper). The database can be found in SSVB21_S3 in the hecedsm package. You can also download the SPSS database via this link.

  1. Have a quick look at the exclusion guidelines in the preregistration. Do they make sense? think about other potential criteria that could have been listed.
  2. Write down potential improvement points related to statistics and experimental setup that you could raise if you were assigned to peer-review the paper.
  3. The author proceed with splitting the data set in three groups and performing each pairwise comparisons in turn, corresponding to the different hypotheses (circa lines 499-533 of the script). Why might this approach be suboptimal relative to the one that consists in fitting a model to the three categories (pooled variance) and proceeding later with computing pairwise differences and contrasts?
  4. Test the assumptions of
    1. equal variance per experimental condition with the ANCOVA
    2. proper randomization based only on Prior scores
    3. equality of slopes
  5. If the variance are unequal, fit the model with unequal variances per group (see the ANCOVA example) — otherwise proceed as usual.
    • Look at the pairwise difference between between Boost+ and consensus only condition and report the results of this test.
    • Does the conclusion of the test change relative to that reported in the paper?


Stekelenburg, A. van, Schaap, G., Veling, H., & Buijzen, M. (2021). Boosting understanding and identification of scientific consensus can help to correct false beliefs. Psychological Science, 32(10), 1549–1565.