The “ever-vaccinated” stock–flow bias in adult RSV vaccine policy evaluation: A methodological caution and a flow-based remedy

= .008 post hoc, did not persist); these underpowered analyses are illustrative only, not identified for the policy effect. To our knowledge, this is the first portable flow-metric operationalization for survey and registry data, released as open code. Registry data exploratorily show the stock metric can obscure equity monitoring (Gini 0.210→0.202; range 39.7→43.5 pp; not significant). As a mid-season snapshot, these figures are an upper bound on the end-of-season value; the conclusion that coverage is dominated by prior-season stock holds through the season. RSV policy evaluation should pre-specify current-season flow as the primary outcome and report the stock share as a strongly recommended diagnostic.