December 12, 2022, Paper: "We document new patterns in investment behavior using a comprehensive dataset of 401(k) plans from 2009 through 2019. We show that there is substantial heterogeneity in asset allocations across plans, which is not explained by differences in available investment options. To understand observed investment behavior, we use a revealed preference approach that allows us to recover heterogeneity in investors’ (subjective) expectations and risk preferences. We demonstrate how exogenous variation in mutual fund expense ratios can nonparametrically identify investors’ expectations and preferences based on their portfolio choices. Our estimates indicate that differences in expectations play a first-order role in explaining portfolios. Further, we show that investors appear to form expectations based on local sources of information such as county-level GDP growth and employer past performance. Overall, our findings are consistent with a model in which heterogeneity in investor expectations reflects idiosyncratic experiences and local environments."