Comparative Cheap Talk

Abstract

When are comparative statements credible? For instance, when can a professor rank different students for an employer, or a stock analyst rank different stocks for a client? We show that simple complementarity conditions ensure that an expert with private information about multiple issues can credibly rank the issues for a decision maker. By restricting the expert's ability to exaggerate, multidimensional cheap talk of this form permits communication when it would not be credible in a single dimension. The communication gains can be substantial with even a couple of issues, and the complete ranking is asymptotically equivalent to full revelation as the number of issues becomes large. Nevertheless, partial rankings are sometimes more credible and/or more profitable for the expert than the complete ranking. We confirm the robustness of comparative cheap talk to asymmetries that are not too large. Moreover, we show that for a sufficiently large number of independent issues there are always some issues sufficiently symmetric to permit influential cheap talk.

Keywords: Multidimensional cheap talk, complementarities

JEL Classification: D82, D74, D72, C72