Learning,diversification and the nature of risk

In many economic settings, faster learning is achievable only through greater exposure to risk. We study this conflict in the context of project choice, where a risk-averse agent must choose whether to invest in two projects of the same type (focus) or of different types (diversification). Focus enables faster learning across periods, but is riskier due to common type-specific shocks. Optimal choice involves balancing these two considerations. We show that focus is preferred for intermediate learning speeds, and that higher prior uncertainty may encourage focus. Thus, what matters for the focus-diversification choice is not only the level of risk, but also whether the risk is permanent or can be “learned away.” We are grateful to two anonymous referees, Serkan Bahceci, Steve Cecchetti, Adam Jaffe, Bojan Jovanovic, Kala Krishna, Blake LeBaron, Rachel McCulloch, Yana Rodgers, participants at the 2004 AEA-CSWEP Meetings and the 2003 North East Universities Development Conference, and seminar participants at Brandeis University for comments and suggestions.