Are individual or institutional investors the agents of bubbles?

Behavioral bubble models typically assume that uninformed trend-chasers, presumably individual investors, cause bubbles, while informed contrarian investors such as institutions, trade against bubbles. DeLong et al. (1990a) highlight that to be considered a "bubble", the mis-pricing must prevail in a large, diversified portfolio. To meet this criterion, we use a unique dataset of all transactions by investor type for all non-financial Korean firms, and find evidence at odds with such assumptions. Domestic individual investors systematically apply aggressive contrarian trades, while foreign and some domestic institutions are mostly trend-chasers. These findings suggest that institutional investors rather than individuals are agents of bubbles.