我国留守儿童健康：现状、成因与影响机制 - 基于异方差限定估计方法和面板数据的实证分析

China has recently undergone large-scale migration, driven primarily by the pursuit of off-farm job opportunities in China’s booming coastal regions, fueling rapid industrialization and urbanization. However, most migrants leave their hometown without their family, which lead to a sizeable Left-behind family in the sending communities. According to the 2010 Census data, the population of left-behind children has reached over 61 million, accounting for about 38 percent of rural children population, and 22 percent of the total children population in China. Due to their lack of parental care, the left-behind children are facing a risky change in their living environment and family structure, and thus raised the concern of many researchers and policy makers. This project aims at understanding the living situation of left-behind children in China over time, estimating the causal impact of parental migration on their health outcomes, as well as exploring the mechanism through which the absence of parenthood caused health problems. Identification is achieved based on Lewbel approach (2012), by having regressors that are uncorrelated with the product of heteroskedastic errors and higher moments, which is a feature of many models where error correlations are due to an unobserved common factor. Particularly, we plan to use data from the China health and nutrition survey 1991-2011, Rural-Urban Migration in China and Indonesia 2008-2013, and China Household Finance Survey 2011-2013 to firstly exam the heterogeneous impact of parental migration- including the duration of parent absence, the timing of migration, and the family migration history- on children’s health. Secondly, we link such impact with the possible effect from intra-household time allocation, grandparent care, nutrition intake, and health facility utilization, to provide policy-makers a better understanding about how parental migration plays a role in children’s health production function.

在我国劳动力大规模流动的背景下，因父母外出务工而留守农村的儿童数目占农村儿童37.7%，占全国儿童21.9%。由于父母照料角色的缺失, 这一群体面临着生活和成长环境的剧烈变动。本课题研究现今农村留守儿童的健康状况、父母外出务工对其健康状况产生的影响、这些影响的形成机理，以及政策制定者如何在现有条件下规避风险。立足于面板数据和最新的Lewbel估计方法(2012)，本项目利用自变量与异方差的协方差矩阵的独立性和高阶矩条件来识别父母移民和其子女健康的因果关系，从而解决文献普遍面临的内生性和有效工具变量缺失的问题。本课题具体考察了不同的移民时长、移民时机（父母离开时儿童的年龄）、家庭移民经历（累积效果与当期效果）对子女健康的异质性影响，并且从家庭成员时间分配、留守模式、营养摄取、和卫生服务利用等多方面分析父母移民对其子女健康造成影响的原因，最后给出相关政策建议。

伴随着快速的经济发展和产业变革, 我国正经历着前所未有的大规模人口流动。值得注意的是，这一现象并不囿于传统研究中关注的城乡移民。随着着城市化进程的深入，相当数目的城市劳动力也开始进行城市间的流动，成为新生代的城城移民。本研究首先考察移民群里的人口特征、地理分布以及影响因素，然后进一步探索城镇化进程中微观家庭受到的影响。根据2013年中国家庭金融调查（CHFS）数据，中国每10个居民中，就有1个人是移民；每3个移民中，就有1个是城市移民。目前，我国城市间移民依然存在“孔雀东南飞”的趋势，大量的人口从中西部流向东部，近年西部地区接受的移民的数量开始逐渐增加。移民目的地的选择主要受到当地的经济发展情况，社会福利情况以及自然环境因素的影响。同时，城市的人口组成，特别是人力资本聚集程度也开始成为吸引移民的重要因素。考虑到中国产业正从东部向中西部转移，而面临劳动力流失的中国中部地区和小城市将在未来的经济增长中面临严峻的挑战。从家庭成员的角度，我国城乡初中学生在认知能力上存在巨大差距。根据中国教育追踪调查（CEPS）2013-2014年度数据研究显示，大约一半的城乡差距是由于可见特征的差异造成，尤其是兄弟姊妹数量，父母教育以及父母和老师的互动等。基于这些结果，儿童早期干预政策包括父母育儿知识培训、学前教育义务化、对特定家庭的儿童早期教育补贴有助于缩小城乡学生认知能力差距。此外，由于父母外出务工而不能和父母生活在一起的儿童在发育指标和患病率方面都有处于明显的劣势。可能的原因是父母由于外出务工不在子女身边而导致对子女缺乏照料，或者由于家庭劳动力的急缺，迫使留守子女承担更多的农业劳动和家务活。从长期来看，有移民经历的家庭通过社会学习，更重视对子女健康的投入，具体表现为更好饮食习惯，营养摄入，就医观念，医疗保险的消费等等。