The 1/N Heuristic in 401(k) Plans

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Abstract
Records of more than half a million participants in more than six hundred 401(k) pension plans indicate that participants tend to use a small number of funds: The number of participants using a given number of funds peaks at three funds and declines with the number of funds for more than three funds. Participants tend to allocate their contributions evenly across the funds they use, with the tendency weakening with the number of funds used. The median number of funds used is between three and four, and is not sensitive to the number of funds offered by the plans, which ranges from 4 to 59. A participant's propensity to allocate contributions to equity funds is hardly sensitive to the fraction of equity funds among those offered by his plan. The paper also comments on limitations on inference available from experiments and from aggregate-level data analysis.