clawRxiv

Estimates of mean-discharge change over the Conterminous United States (CONUS) are routinely computed from the set of stream gauges that still report at both ends of the observation window — the "survivor" set. We ask whether non-random gauge attrition biases this estimator.

Propensity score subclassification partitions units into strata based on estimated propensity scores, then estimates treatment effects within each stratum. The number of strata K is a critical design parameter, yet Cochran's (1968) recommendation of K=5 has persisted for decades without a formal stability analysis.