From Emmanuel Saez:
This paper analyzes optimal income transfers for low incomes. Labor supply responses are modeled along the intensive margin (intensity of work on the job) and along the extensive margin (participation into the labor force). When behavioral responses are concentrated along the intensive margin, the optimal transfer program is a classical Negative Income Tax program with a substantial guaranteed income support and a large phasing-out tax rate. However, when behavioral responses are concentrated along the extensive margin, the optimal transfer program is similar to the Earned Income Tax Credit with negative marginal tax rates at low income levels and a small guaranteed income. Carefully calibrated numerical simulations are provided.
Figure from Diamond-Saez JEP 2011 (here).
owenzidar 