Fig 2. Types of interactions.

Each panel shows a qualitatively different outcome of a 2 × 2 factorial design. The first panel (from left) shows two main effects without an interaction. The second panel shows an (additive) interaction but no main effect. The remaining three panels show different constellations of two main effects accompanied by an interaction. Crucially the relative order of the conditions differs across these three constellations. The five displayed outcomes are used in the simulations.