Machine Forecast Disagreement

We propose a statistical model of differences in beliefs in which heterogeneous investors are represented as different machine learning model specifications.Each investor forms return forecasts from their own specific model using data inputs that are available to all investors.We measure disagreement as dispersion in forecasts across investor-models.Our measure aligns with extant measures of disagreement (e.g., analyst forecast dispersion), but is a significantly stronger predictor of future returns.We document a large, significant, and highly robust negative crosssectional relation between belief disagreement and future returns.A decile spread portfolio that is short stocks with high forecast disagreement and long stocks with low disagreement earns a value-weighted alpha of 15% per year.A range of analyses suggest the alpha is mispricing induced by short-sale costs and limits-to-arbitrage.