 Validity is proven by other means, including deliberately balanced and stratified experiments, small series of independent and repeated samples controlling for real not merely random error, and an economic approach to the logic of uncertainty.His work showing the history and power of balanced over randomized controlled trials, rival techniques which Ziliak traces back to the early 1900s and the Guinness Brewery in Dublin, has been noted by Tim Harford, Casey Mulligan, and others for its deep challenge to randomized field experiments after John List, Steve Levitt, Esther Duflo, and others.In July 2008 Ziliak was invited by the International Biometric Society and the Irish Statistical Association to present his work in Dublin on "Guinnessometrics