Figure 4.

(A) Hypothetical network illustrating an inverted fork type of path configuration in the context of piglet behavior (Merk Manual Veterinary Manual Online at http://www.merckvetmanual.com/behavior/normal-social-behavior-and-behavioral-problems-of-domestic-animals/behavioral-problems-of-swine). (B) The same network is depicted where conditioning (represented in gray) on either aggressive behavior (D₃) or mortality (D₄) creates a spurious association between overcrowding (D₁) and mixing (D₂), represented by the double-headed dashed arrow line. (C) Scatterplot of groups of pigs that either showed aggressive behavior (•) or did not (°), characterized by animal density (expressed as number of piglets/m²) and level of mixing (expressed as number of litters mixed).