It should be clear of course that for traders to have incentives to gather information required that information not be perfectly disseminated in the… - Joseph E. Stiglitz

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It should be clear of course that for traders to have incentives to gather information required that information not be perfectly disseminated in the market. If, simply by looking at market prices, those who do not spend money to acquire information can glean all the information that the informed traders who have spent money to acquire information have, then the informed traders will not have any informational advantage; they will not be able to obtain any return to their expenditures on information acquisition. Accordingly, if there were a complete set of markets, information would be so well conveyed that investors would have no incentives to gather information. (Of course with all participants having the same [zero] information, incentives to trade would be greatly reduced.) To put the matter differently, the assumptions of "informed" markets and "a complete set of markets" may be mutually exclusive.