Limits of rcts Balance between treatment and control groups occurs only in expectation Sample is a trial sample, rarely a true random sample from population Most rcts in economics are still not double blinded Stable Unit Treatment Value Assumption ( SUTVA) Average treatment effects only identified if no spillovers GE Spillovers are important features of key trade insights (e. g. Eaton and Kortum 02: Hornbeck donaldson 16 External validity Good RCTs work hard to generate externally-valid research designs Can be achieved over time through many studiesLimits of RCTs • Balance between treatment and control groups occurs only in expectation – Sample is a trial sample, rarely a true random sample from population • Most RCTs in economics are still not double blinded • Stable Unit Treatment Value Assumption (SUTVA) – Average treatment effects only identified if no spillovers – GE/Spillovers are important features of key trade insights (e.g., Eaton and Kortum 02; Hornbeck Donaldson 16) • External validity – Good RCTs work hard to generate externally-valid research designs – Can be achieved over time through many studies 7