Stock market behavior of individual investors is highly correlated with stock market behavior of their co-workers. For example, a ten percentage point increase in the fraction of co-workers that purchase stocks in a given month is associated with a two percentage point increase in the likelihood...

Stock market investment decisions of individuals are positively correlated with that of co-workers. Sorting of unobservably similar individuals to the same workplaces is unlikely to explain our results, as evidenced by the investment behavior of individuals that move between plants. Purchases...