Investment in concealable information by biased experts

We study a persuasion game in which biased—possibly opposed—experts strategically acquire costly information that they can then conceal or reveal. We show that information acquisition decisions are strategic substitutes when experts have linear preferences over a decision maker's beliefs. The logic turns on how each expert expects the decision maker's posterior to be affected by the presence of other experts should he not acquire information that would turn out to be favorable. The decision maker may prefer to solicit advice from just one biased expert even when others—including those biased in the opposite direction (singular)—are available.