Combining Forecasts From Advisors: The Impact of Advice Independence and Verbal Versus Numeric Format.

Past research on advice-taking has suggested that people are often insensitive to the level of advice independence when combining forecasts from advisors. However, this has primarily been tested for cases in which people receive numeric forecasts. Recent work by Mislavsky and Gaertig (2022) shows that people sometimes employ different strategies when combining verbal versus numeric forecasts about the likelihood of future events. Specifically, likelihood judgments based on two verbal forecasts (e.g., "rather likely") are more often extreme (relative to the forecasts) than are likelihood judgments based on two numeric forecasts (e.g., "70% probability"). The goal of the present research was to investigate whether advice-takers' use of combination strategies can be sensitive to advice independence when differences in independence are highly salient and whether sensitivity to advice independence depends on the format in which advice is given. In two studies, we found that advice-takers became more extreme with their own likelihood estimate when combining forecasts from advisors who use separate evidence, as opposed to the same evidence. We also found that two verbal forecasts generally resulted in more extreme combined likelihood estimates than two numeric forecasts. However, the results did not suggest that sensitivity to advice independence depends on the format of advice. Public Significance Statement: An important factor when combining forecasts from advisors is whether advisors are relying on the same or separate evidence to generate their forecasts. People have often been found to be insensitive to such differences in advisor independence. However, in the present work, we found that people can indeed use information about advice independence in a normative matter when differences in advice independence are sufficiently salient. Importantly, we also found that this sensitivity was not moderated by the format in which forecasts are presented. Participants in our studies attended to advice independence both when forecasts were in a verbal format (e.g., rather likely) and when both were in a numeric format (e.g., 70% probability). Replicating prior work (Mislavsky & Gaertig, 2022; Teigen et al., 2023), we also found evidence of a general advice format effect: When combining verbal as opposed to numeric forecasts, people's final likelihood estimates became more extreme (closer to certainty). [ABSTRACT FROM AUTHOR]