Researchers often hold out data from the estimation of econometric models to use for external validation. However, the use of holdout samples is suboptimal from a Bayesian perspective, which prescribes using the entire sample to form posterior model weights. This paper examines a possible
rationale for the use of holdout samples: data-inspired modifications of structural models are likely to lead to an exaggeration of model fit. The use of holdout samples can, in principle, set an incentive for the modeler not to exaggerate model fit.
The American Economic Review is a general-interest economics journal. The journal is published quarterly and contains articles on a broad range of topics. Established in 1911, the AER is among the nation's oldest and most respected scholarly journals in the economics profession.