Distributional overlap means that two groups share values within the ranges of their distributions. With propensity scores, overlap provides comparable treated and control patients at similar scores. section 5.3.3
Propensity-score distributions
If treated patients have scores from 0.55 to 1 and controls from 0 to 0.5, the supports do not overlap, assignment is deterministic, and the positivity assumption fails. If both groups span roughly 0 to 1, overlap is full and ATE calculation can proceed. With overlap only from 0.25 to 0.75, restrict ATE analysis to that common-support region. section 5.3.3
Figure 5.11 Partial overlap in a distribution’s supports. We can calculate the ATE only for patients within the common support region.
Use the partial-overlap figure to identify the common-support region and see why ATE estimation is limited to patients inside it. section 5.3.3
