Five synthetic markets, each with its truth built in: two platforms’ reported reach and what the site saw: visitors from each, and visitors from both. The method counts the visitors exactly, then turns the visitors from both into a floor on the unique reach, sets a ceiling from the chance formula, and refuses a point in between. Move the shared-visitor count and watch the floor and its interval move. Move the keenness to see how far a floor can be from the truth, and move the population to see the ceiling. The figures here are pooled. The stratified floor (the same arithmetic within a segment both platforms report, then summed) lives in the notebook. Synthetic data throughout.
Self-check: running…