TY - JOUR A1 - Rosenzweig, M.R. A1 - Wolpin, K.I. T1 - Testing the Quantity-Quality Fertility Model: The Use of Twins as a Natural Experiment Y1 - 1980 DO - 10.2307/1912026 JF - Econometrica VL - 48 IS - 1 SP - 227 EP - -240 ER -