上大学会多大程度上推迟初婚年龄?——基于IV-Tobit模型的估计

How Does Higher Education Delay the Age at the First Marriage?——Estimate Based on the IV-Tobit Model

在估计高等教育会多大程度上推迟初婚年龄时会同时面临生存数据结构(Duration data)与内生性问题,以往文献无法很好地解决这个问题。基于已有研究方法,本文设计了一种计量策略来解决这一问题。首先将该问题等价转化为研究在给定年龄的条件下高等教育对已婚时间的影响,从而将数据转化为一个单方向截尾的数据结构并使用Tobit模型进行估计。然后用是否在扩招后参加高考作为高等教育的工具变量,用IV-Tobit模型估计高等教育对初婚年龄的推迟效应。估计结果显示,相对于高中毕业生,每多接受1年高等教育平均初婚年龄将推迟1.5年;相应地,大专、本科教育会将初婚年龄推迟4.5和6年。由于女性生育存在一个最佳的年龄阶段,因此该推迟效应可能会严重影响生育率和母婴健康。另外,高等教育对男性初婚推迟的效应大于女性,对非农业户口的影响大于农业户口,在东、中、西部地区没有差异。本文发现这种推迟效应主要是在校接受高等教育带来的顺延,高等教育并没有显著降低接受者的结婚意愿,上大学只是推迟婚姻,而不是终身不婚。人口普查数据显示我国高等教育人口与较低教育人口的最终结婚率几乎没有差异。不同于其他发达国家,我国的高等教育群体仍然具有较高的结婚率。政府应该采取积极措施降低他们步入婚姻的经济成本,延缓这种婚姻推迟的趋势。

It is usually hard to estimate the causal effect of higher education on the age at the first marriage because of the existence of endogeneity problem in a duration data. In this paper,we try to solve this problem using IV-Tobit model to a transformed data. First,we transform the research question on the effect of higher education on the years since the marriage till the survey year,which is censored from the left. Second,we use Tobit and IV-Tobit models to estimate the effect of higher education on years since the marriage. Using the natural experiment,the higher education expansion since 1999,as the instrument,we find that higher education delays the age at the first marriage. Compared to the case had not admitted to colleges/ universities,one additional year of higher education postpones the first marriage by 1.5 years. This corresponds 4-6 years postpone of the age of the first marriage due to the higher education. Given that there is an optimal fertility age period for women,this 4-6 years of postpone may have a strong negative effect on fertility and maternal and child health. In addition,we find the delay effect is stronger for the male than female,greater for the non-agriculture Hukou than agricultural Hukou,and has no difference across regions. We also find that this delay effect is mainly due to the extra years of higher education,and does not find higher education changes the willingness to marry. Different from other developed countries,the higher education group of China remains a high marriage rate. The government should take active measures to decrease the economic cost of their marriage and slow down their marriage delay trend.