Selection Bias: Interactive Explorer

Drag the ellipse handles to define the enrollment zone. Adjust sliders to set each group's probability of being assigned to treatment.

General Population n = 90

Drag handles to resize/move the enrollment zone

Study Population n = ?

Treatment ?

Control ?

STEP 1 Enrollment Zone

Drag the blue center handle to move, red edge handles to resize

enrolled

enrollment rate

STEP 2 Assignment Weights by Group

P(treatment) for each group; top 50% of scored enrollees receive treatment

① Sample Selection Bias

TVD = —

TVD = ½ Σ|study_i − pop_i| 0 = fully representative · 0.8 = maximally biased (5 groups)

② Selection Bias in Assignment

TVD = —

TVD = ½ Σ|treat_i − ctrl_i| 0 = balanced groups · higher = systematic confounding