PMC

Illustration of collider stratification bias.

Association (OR) between A and Y in the null case for varying values of α_A,α_U, β_U, and α_AU. In each panel, along the x axis, one of these variables is varied from −3 to 3 (left panel: α_A, mid-left panel: α_U, mid-right panel: β_U, right panel: α_AU), and the other parameters are set to default values.

Association (OR) between A and Y in the null case for varying values of α_A,α_U, and β_U, without interaction (α_AU = 0, solid line) and with interaction (α_AU = 1, dotted line). Each column (row) in the lattice corresponds to the given value of β_U (α_A). Within each subgraph, along the x axis, α_U is varied from −3 to 3.

Association (OR) between A and Y versus causal effect (log odds) of A on Y for varying values of α_A,α_U, and β_U, with β_B = 1. Each column (row) in the lattice corresponds to the given of β_U (α_A). Within each subgraph, along the x axis, α_U is varied from −3 to 3. Association without interaction (α_AU = 0): solid line; association with interaction (α_AU = 1): dotted line; causal effect: dashed line.

Association (OR) between A and Y (solid line) versus causal effect (log odds) of A on Y (dashed line) for a range of values of α_A,α_U, β_U, and α_AU. In each panel, along the x axis, one of these variables is varied from −3 to 3 (left panel: α_A, mid-left panel: α_U, mid-right panel: β_U, right panel: α_AU), and the other parameters are set to default values.