Estimating Returns to Education Using Different Natural Experiment Techniques

We compare three quasi-experimental approaches to estimating the returns to schooling in Australia: instrumenting schooling using month of birth, instrumenting schooling using changes in compulsory schooling laws, and comparing outcomes for twins. With annual pre-tax income as our measure of income, we find that the naïve (OLS) returns to an additional year of schooling is 13%. The month of birth IV approach gives an 8% rate of return to schooling, while using changes in compulsory schooling laws as an IV produces a 12% rate of return. Finally, we review estimates from twins studies. While these studies have tended to estimate a lower return to education, we believe that this is primarily due to the better measurement of income and schooling in our dataset. Australian twins studies are consistent with our findings insofar as they find little evidence of ability bias in the OLS rate of return to schooling. Our estimates of the ability bias in OLS estimates of the rate of return to schooling range from 9% to 39%. Overall, our findings suggest the Australian rate of return to education, corrected for ability bias, is around 10%, which is similar to the rate in Britain, Canada, the Netherlands, Norway and the United States.

本研究针对澳大利亚教育回报率的估算问题，对比了三类准实验研究方法：以出生月份作为教育年限的工具变量（Instrumental Variable, IV）、利用义务教育法案修订作为教育年限的工具变量，以及通过双胞胎样本对比法。以年度税前收入作为收入的衡量标准，本文发现朴素普通最小二乘法（OLS）估计得到的每增加一年教育的回报率为13%。出生月份工具变量法得到的教育回报率为8%，而以义务教育法案修订作为工具变量的估计结果则为12%。最后，本文梳理了双胞胎研究的相关估计结果。尽管过往双胞胎研究往往得到更低的教育回报率，但我们认为这主要源于本数据集对收入与教育水平的测量更为精准。澳大利亚本土的双胞胎研究结论与本文结果一致，均未发现教育回报率OLS估计中存在显著的能力偏差。本文对教育回报率OLS估计中能力偏差的估计值介于9%至39%之间。综合来看，本文结果表明，经能力偏差修正后的澳大利亚教育回报率约为10%，这一水平与英国、加拿大、荷兰、挪威及美国的教育回报率相近。