“Tell all the truth, but tell it slant”: Documenting media bias

Media outlets often appear to bias news reports, but it is often difficult to document bias cleanly and to ascribe motivation when bias is detected. We test for media bias in a novel setting. We show that in the late 19th century The New York Times weather reports were correlated with the schedule of the Giants, the local professional baseball team: On home game days weather reports were more “optimistic” (i.e., relatively more accurate at predicting sunny weather). The size of optimism is large — when producing in-house forecasts, The New York Times predicted fair weather 14.2 percentage points more often on days when the Giants were scheduled to play at home. We provide a framework for evaluating such bias, and show that the bias is consistent with a demand-driven motivation.