Estimates of the Economic Return to Schooling from a New Sample of Twins

Abstract

This paper uses a new survey to contrast the wages of genetically identical twins with different schooling levels. Multiple measurements of schooling levels were also collected to assess the effect of reporting error on the estimated economic returns to schooling. The data indicate that omitted ability variables do not bias the estimated return to schooling upward, but that measurement error does bias it downward. Adjustment for measurement error indicates that an additional year of schooling increases wages by 12-16 percent, a higher estimate of the economic retums to schooling than has been previously found. (JEL J31) This paper uses a new survey of identical twins to study the economic returns to schooling. We estimate the returns to schooling by contrasting the wage rates of identical twins with different schooling levels. Our goal is to ensure that the correlation we observe between schooling and wage rates is not due to a correlation between schooling and a worker's ability or other characteristics. We do this by taking advantage of the fact that monozygotic (from the same egg) twins are genetically identical and have similar family backgrounds. In our survey we also took some unusual steps to measure a worker's schooling level accurately. We obtained independent estimates of each sibling's schooling level by asking the twins to report on both their own and their twin's schooling. These new data provide a simple and powerful method for assessing the role of measurement error in estimates of the economic returns to schooling.