Past exam of the experimental design and methods course of the year 2 of the psychology (experimental) course of the University of Oxford / 2022 / 5 / e / Solution

TODO: no definite follow-up decision can be made without the fitted model, uncertainty and diagnostics. An included interaction can be clarified with simple-effects analysis, fitted cell summaries and confidence intervals on scientifically relevant differences. If the study aims to test whether the predictors combine additively but only an additive model was fitted, an adequately supported, prespecified interaction comparison may be relevant. Respect multiple testing when several comparisons are examined.

Check model fit, influential observations and heteroscedasticity; a response bounded between zero and one thousand may require particular care near its bounds, but that scale alone does not choose a replacement model. If observations are dependent, the analysis must account for that structure. Such checks are possible recommendations; the missing supplementary sheet prevents identifying which problems, if any, actually occurred.