This article provides a microfoundation for the rise in optimism that seems to precede market crashes. Small, young markets are more likely to experience stock-price run-ups and crashes. We use a Zeira-Rob type of model in which demand size is uncertain. Optimism then grows rationally if...

Stock-market crashes tend to follow run-ups in prices. These episodes look like bubbles that gradually inflate and then suddenly burst. We show that such bubbles can form in a Zeira-Rob type of model in which demand size is uncertain. Two conditions are sufficient for this to happen: A declining...

Stock-market crashes tend to follow run-ups in prices. These episodes look like bubbles that gradually inflate and then suddenly burst. We show that such bubbles can form in a Zeira-Rob type of model in which demand size is uncertain. Two conditions are sufficient for this to happen: A declining...