智慧元素的力量:碘缺乏病防治对我国经济发展的长期影响
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摘要
碘缺乏病曾是广泛威胁我国民众健康,并对婴幼儿智力发育有着严重阻碍的疾病。我国政府于20世纪70年代中后期开展的大规模补碘运动显著地改善了民众的碘营养状况,因而很可能通过提升个体智力水平而对人力资本积累和经济发展产生深远影响。文章利用2012年中国劳动力动态调查微观数据,对碘缺乏病防治的长期影响进行考察。双重差分的估计结果显示,尽管婴幼儿时期补碘对身高的影响并不明显,但却能够显著地提高个体受教育年限和年收入水平;并且补碘对教育的影响主要产生于初中阶段,对小学阶段和高中阶段的影响并不显著。此外,研究还发现胎儿期是补碘的关键时期,出生后补碘对个体的影响较小。因此,加强对盐业市场的监管,增强民众的补碘意识,对我国的经济发展和脱贫工作有着极其重要的意义。
Disease is an important factor affecting economic development. Researches show the diseases like malaria,hookworm and HIV can significantly impede the human capital accumulation and economic development in the endemic regions around the world. Compared with diseases caused by parasite or virus,the diseases caused by micronutrients deficiency are less noticed. However,the impact of micronutrients deficiency could be severe,especially the deficiency of iodine. Iodine deficiency during pregnancy can hamper the brain development of fetus,leading to permanent intelligence damage. Because intelligence is an important factor for human capital accumulation,the widespread popularity of iodine deficiency is likely to have a negative impact on economic development.China's large-scale campaign to prevent and control iodine deficiency since 1970s could have significant impacts on economic development. Before the campaign,endemic iodine deficiency was found among all the provincial administration regions except Shanghai; the number of iodine deficiency patients was estimated to be 35 million; about 200 thousand people were diagnosed as cretinism; and the population whose intelligence was slightly affected by iodine deficiency(subclinical cretinism)could be much larger than cretinism. Considering the severe threat of iodine deficiency,the Chinese government launched a large-scale campaign of iodine supplementation across the country since 1975. By 1985,83.23% of the endemic countries and 87.3% of the population in endemic regions had been covered by salt iodization program. More than 22 million iodine deficiency patients had been treated in this period,and the birthrate of cretinism had been decreased by a great magnitude. Since the iodine supplementation campaign improved the iodine nutrition for a large population of China,it's likely to increase people's intelligence and affect human capital accumulation and economic development in China deeply.This paper studies the long-term impact of iodine supplementation on individual height,education and income by using the micro data provided by China Labor-force Dynamic Survey(CLDS)in 2012. Difference-in-difference model is used as our empirical strategy. The results show that:iodine supplementation during the early childhood has no significant impact on individual height,but iodine supplementation significantly improves individual education and income. If the incidence of cretinism increased by 1‰ before the iodine supplementation,the years of education for individuals born in that region after the iodine supplementation would increase by 0.562 year while the annual income would increase by 7.83%. Besides,we find the fetal stage is the most important period for iodine supplementation,and the effect of iodine supplementation after fetal stage is much smaller. Therefore,iodine supplementation is an effective measure to boost economic growth by improving people's intelligence and promoting human capital accumulation.This paper contributes to the current researches in the following aspects. Firstly,for the remarkable economic growth of China since the reform and opening-up policy,although many scholars have provided the explanation from the channels like political institution,economic institution and infrastructure,little attention has been paid to the important role of large-scale campaign of disease prevention and treatment.Thus,this paper deepens our understanding of China's economic miracle from a new perspective. Secondly,by studying the long-term impact of iodine deficiency prevention campaign,this paper also enriches the field of the long-term impact of historical events. Finally,our empirical findings provide guidance for the further insurance of people's iodine nutrition and prevention of intelligence damage in poor regions.
Disease is an important factor affecting economic development. Researches show the diseases like malaria,hookworm and HIV can significantly impede the human capital accumulation and economic development in the endemic regions around the world. Compared with diseases caused by parasite or virus,the diseases caused by micronutrients deficiency are less noticed. However,the impact of micronutrients deficiency could be severe,especially the deficiency of iodine. Iodine deficiency during pregnancy can hamper the brain development of fetus,leading to permanent intelligence damage. Because intelligence is an important factor for human capital accumulation,the widespread popularity of iodine deficiency is likely to have a negative impact on economic development.China's large-scale campaign to prevent and control iodine deficiency since 1970s could have significant impacts on economic development. Before the campaign,endemic iodine deficiency was found among all the provincial administration regions except Shanghai; the number of iodine deficiency patients was estimated to be 35 million; about 200 thousand people were diagnosed as cretinism; and the population whose intelligence was slightly affected by iodine deficiency(subclinical cretinism)could be much larger than cretinism. Considering the severe threat of iodine deficiency,the Chinese government launched a large-scale campaign of iodine supplementation across the country since 1975. By 1985,83.23% of the endemic countries and 87.3% of the population in endemic regions had been covered by salt iodization program. More than 22 million iodine deficiency patients had been treated in this period,and the birthrate of cretinism had been decreased by a great magnitude. Since the iodine supplementation campaign improved the iodine nutrition for a large population of China,it's likely to increase people's intelligence and affect human capital accumulation and economic development in China deeply.This paper studies the long-term impact of iodine supplementation on individual height,education and income by using the micro data provided by China Labor-force Dynamic Survey(CLDS)in 2012. Difference-in-difference model is used as our empirical strategy. The results show that:iodine supplementation during the early childhood has no significant impact on individual height,but iodine supplementation significantly improves individual education and income. If the incidence of cretinism increased by 1‰ before the iodine supplementation,the years of education for individuals born in that region after the iodine supplementation would increase by 0.562 year while the annual income would increase by 7.83%. Besides,we find the fetal stage is the most important period for iodine supplementation,and the effect of iodine supplementation after fetal stage is much smaller. Therefore,iodine supplementation is an effective measure to boost economic growth by improving people's intelligence and promoting human capital accumulation.This paper contributes to the current researches in the following aspects. Firstly,for the remarkable economic growth of China since the reform and opening-up policy,although many scholars have provided the explanation from the channels like political institution,economic institution and infrastructure,little attention has been paid to the important role of large-scale campaign of disease prevention and treatment.Thus,this paper deepens our understanding of China's economic miracle from a new perspective. Secondly,by studying the long-term impact of iodine deficiency prevention campaign,this paper also enriches the field of the long-term impact of historical events. Finally,our empirical findings provide guidance for the further insurance of people's iodine nutrition and prevention of intelligence damage in poor regions.
引文
[1]陈吉祥,李忠之,许弘凯.95中国碘缺乏病监测[M].北京:人民卫生出版社,1999.
[2]陈祖培.全民食盐加碘的意义及对当前人群碘营养状况的基本评价[J].中国地方病防治杂志,2002,(4):251-254.
[3]龚胜生.2000年来中国地甲病的地理分布变迁[J].地理学报,1999,(4):335-346.
[4]李楠,林友宏.管治方式转变与经济发展——基于清代西南地区“改土归流”历史经验的考察[J].经济研究,2016,(7):173-188.
[5]李楠,卫辛.新中国血吸虫病防治对人口增长影响的实证分析(1953-1990)[J].中国经济史研究,2017,(1):84-95.
[6]马泰,卢倜章,于志恒.碘缺乏病:地方性甲状腺肿与地方性克汀病[M].北京:人民卫生出版社,1993.
[7]谭见安.中华人民共和国地方病与环境图集[M].北京:科学出版社,1989.
[8]滕瑞涛.我国地甲病防治现状及今后工作的展望[J].实用地方病学杂志,1986,(3):50-55.
[9]肖东楼,孙殿军,白呼群,等.2005年中国碘缺乏病监测[M].北京:人民卫生出版社,2007.
[10]中华人民共和国卫生部地方病防治司.碘缺乏病防治手册[M].哈尔滨:中国地方病防治研究中心,1989.
[11]Acemoglu D,Johnson S,Robinson J A.The colonial origins of comparative development:An empirical investigation[J].The American Economic Review,2001,91(5):1369-1401.
[12]Alsan M.The effect of the tsetse fly on African development[J].American Economic Review,2015,105(1):382-410.
[13]Bleakley H.Disease and development:Evidence from hookworm eradication in the American South[J].The Quarterly Journal of Economics,2007,122(1):73-117.
[14]Bleakley H.Malaria eradication in the Americas:A retrospective analysis of childhood exposure[J].American Economic Journal:Applied Economics,2010,2(2):1-45.
[15]Cutler D,Fung W,Kremer M,et al.Early-life malaria exposure and adult outcomes:Evidence from malaria eradication in India[J].American Economic Journal:Applied Economics,2010,2(2):72-94.
[16]Feyrer J,Politi D,Weil D N.The cognitive effects of micronutrient deficiency:Evidence from salt iodization in the United States[J].Journal of the European Economic Association,2017,15(2):355-387.
[17]Field E,Robles O,Torero M.Iodine deficiency and schooling attainment in Tanzania[J].American Economic Journal:Applied Economics,2009,1(4):140-169.
[18]Fortson J G.Mortality risk and human capital investment:The impact of HIV/AIDS in Sub-Saharan Africa[J].The Review of Economics and Statistics,2011,93(1):1-15.
[19]Gallup J L,Sachs J D.The economic burden of malaria[J].The American Journal of Tropical Medicine and Hygiene,2001,64(S1-2):85-96.
[20]Politi D.The impact of iodine deficiency eradication on schooling:Evidence from the introduction of iodized salt in Switzerland[R].Working Paper,2010.
[21]Venkataramani A S.Early life exposure to malaria and cognition in adulthood:Evidence from Mexico[J].Journal of Health Economics,2012,31(5):767-780.
(1)关于历史文献中对碘缺乏病的记载及其所反映的碘缺乏病分布概况,可参见龚胜生(1999)。
(2)例如,姚寻源等于1940-1942年对云南省37个县的碘缺乏病情况进行了调查,查出甲状腺肿大患者28 879例,平均患病率15.4%。参见《云南省志·卫生志》(2002)。
(1)当时的克汀病诊断标准为:出生、居住于低碘地方性甲状腺肿病区、有精神发育不全(不同程度的智力障碍),具有神经系统或甲状腺功能低下症,并排除了分娩损伤、脑炎、脑膜炎及药物中毒等病史者(参见1981年地方性克汀病诊断标准)。
(2)限于篇幅,未给出关于防治前我国碘缺乏病的详细分布情况。需要者可向作者索取。
(3)相关调查依据的亚克汀病诊断标准为:出生、居住于低碘地方性甲状腺肿、地方性克汀病流行区,有轻度智力落后(智商在69-50之间),并伴有轻微神经系统损伤、体格发育障碍或激素性甲状腺功能低下的人。参见《碘缺乏病防治手册》(中华人民共和国卫生部地方病防治司,1989)。
(4)针对全国范围内亚克汀病患者的数量统计并未有过系统的调查,20世纪90年代曾有学者估计亚克汀病患者数为800余万人(祁嘉义,2000)。
(5)相关数据来自滕瑞涛(1986)。
(6)尽管并没有针对全国新生克汀病儿的统计数据,但许多地区性的研究都证实了克汀病患儿出生率在供应碘盐后的大幅下降。例如,朱宪彝(1981)发现,贵州东南部某公社供应碘盐前两年的克汀病患儿出生率为70%,供碘后一年内克汀病患儿出生率仅为1/60。
(7)20世纪80年代后期非碘盐的大规模冲击,使得许多病区病情严重回升。例如,1988年全国碘缺乏地区流入的非碘盐竟占碘盐需求量的1/6(何光临,1991)。
(8)我国于1994年和1995年相继实施食盐专营政策和全民食用加碘盐政策,使得非碘盐冲击问题得到显著的改观(王海潜,1994;谭洽,1996;陈吉祥等,1999;肖东楼等,2007)。
(1)如需了解有关此数据的更多信息,请登录http://css.sysu.edu.cn。
(2)目前,双重差分模型已被广泛用于对疾病防治影响的考察,具体参见Bleakley(2010)、Cutler等(2010)和Lucas(2010)的研究。
(1)高林等(1992)调查了甘肃两个乡,其中重病区乡的克汀病患病率为1.19%,亚克汀病患病率为24%;轻病区乡的克汀病患病率为0.72%,亚克汀病患病率为4%。
(2)由于图集只显示了各县市患病率所属的区间,因而我们用所属区间的中间值作为真实患病率的近似。如果克汀病患病率位于小于0.05%的区间,则近似值为0.025%;患病率位于0.05%-0.20%区间,则近似值为0.125%;患病率位于0.20%-0.50%区间,则近似值为0.35%;患病率位于0.50%-1%区间,则近似值为0.75%;患病率>1%,则近似值为1.15%。
(3)出身类型包括贫(雇)农、下中农、富裕中农、工人等13类;职业类型为第五次全国人口普查所使用的职业分类。
(1)这里的出生年份维度是分省别的,即年龄相同但省份不同的个体被设为不同的聚类。这是由于本研究的双重差分模型控制了省级固定效应与个体出生时期变量的交互项,因而模型在识别补碘影响时比较的是同一省份内部的样本。
(1)例如,包爱民等(2000)发现,6岁以后开始补碘的儿童较同年龄未补碘儿童有着更高的身高。
(1)样本中,小学毕业个体占87.58%,初中毕业个体占65.98%,高中毕业个体占23.29%。
(1)|k|表示对k取绝对值。
(2)这样,补碘开始年份4年前出生个体的区域差异被地区固定效应吸收,无需额外控制。
(1)CLDS调查仅对过去一年内有工作的个体询问年收入情况,因而未工作个体的年收入变量为缺失值。
[2]陈祖培.全民食盐加碘的意义及对当前人群碘营养状况的基本评价[J].中国地方病防治杂志,2002,(4):251-254.
[3]龚胜生.2000年来中国地甲病的地理分布变迁[J].地理学报,1999,(4):335-346.
[4]李楠,林友宏.管治方式转变与经济发展——基于清代西南地区“改土归流”历史经验的考察[J].经济研究,2016,(7):173-188.
[5]李楠,卫辛.新中国血吸虫病防治对人口增长影响的实证分析(1953-1990)[J].中国经济史研究,2017,(1):84-95.
[6]马泰,卢倜章,于志恒.碘缺乏病:地方性甲状腺肿与地方性克汀病[M].北京:人民卫生出版社,1993.
[7]谭见安.中华人民共和国地方病与环境图集[M].北京:科学出版社,1989.
[8]滕瑞涛.我国地甲病防治现状及今后工作的展望[J].实用地方病学杂志,1986,(3):50-55.
[9]肖东楼,孙殿军,白呼群,等.2005年中国碘缺乏病监测[M].北京:人民卫生出版社,2007.
[10]中华人民共和国卫生部地方病防治司.碘缺乏病防治手册[M].哈尔滨:中国地方病防治研究中心,1989.
[11]Acemoglu D,Johnson S,Robinson J A.The colonial origins of comparative development:An empirical investigation[J].The American Economic Review,2001,91(5):1369-1401.
[12]Alsan M.The effect of the tsetse fly on African development[J].American Economic Review,2015,105(1):382-410.
[13]Bleakley H.Disease and development:Evidence from hookworm eradication in the American South[J].The Quarterly Journal of Economics,2007,122(1):73-117.
[14]Bleakley H.Malaria eradication in the Americas:A retrospective analysis of childhood exposure[J].American Economic Journal:Applied Economics,2010,2(2):1-45.
[15]Cutler D,Fung W,Kremer M,et al.Early-life malaria exposure and adult outcomes:Evidence from malaria eradication in India[J].American Economic Journal:Applied Economics,2010,2(2):72-94.
[16]Feyrer J,Politi D,Weil D N.The cognitive effects of micronutrient deficiency:Evidence from salt iodization in the United States[J].Journal of the European Economic Association,2017,15(2):355-387.
[17]Field E,Robles O,Torero M.Iodine deficiency and schooling attainment in Tanzania[J].American Economic Journal:Applied Economics,2009,1(4):140-169.
[18]Fortson J G.Mortality risk and human capital investment:The impact of HIV/AIDS in Sub-Saharan Africa[J].The Review of Economics and Statistics,2011,93(1):1-15.
[19]Gallup J L,Sachs J D.The economic burden of malaria[J].The American Journal of Tropical Medicine and Hygiene,2001,64(S1-2):85-96.
[20]Politi D.The impact of iodine deficiency eradication on schooling:Evidence from the introduction of iodized salt in Switzerland[R].Working Paper,2010.
[21]Venkataramani A S.Early life exposure to malaria and cognition in adulthood:Evidence from Mexico[J].Journal of Health Economics,2012,31(5):767-780.
(1)关于历史文献中对碘缺乏病的记载及其所反映的碘缺乏病分布概况,可参见龚胜生(1999)。
(2)例如,姚寻源等于1940-1942年对云南省37个县的碘缺乏病情况进行了调查,查出甲状腺肿大患者28 879例,平均患病率15.4%。参见《云南省志·卫生志》(2002)。
(1)当时的克汀病诊断标准为:出生、居住于低碘地方性甲状腺肿病区、有精神发育不全(不同程度的智力障碍),具有神经系统或甲状腺功能低下症,并排除了分娩损伤、脑炎、脑膜炎及药物中毒等病史者(参见1981年地方性克汀病诊断标准)。
(2)限于篇幅,未给出关于防治前我国碘缺乏病的详细分布情况。需要者可向作者索取。
(3)相关调查依据的亚克汀病诊断标准为:出生、居住于低碘地方性甲状腺肿、地方性克汀病流行区,有轻度智力落后(智商在69-50之间),并伴有轻微神经系统损伤、体格发育障碍或激素性甲状腺功能低下的人。参见《碘缺乏病防治手册》(中华人民共和国卫生部地方病防治司,1989)。
(4)针对全国范围内亚克汀病患者的数量统计并未有过系统的调查,20世纪90年代曾有学者估计亚克汀病患者数为800余万人(祁嘉义,2000)。
(5)相关数据来自滕瑞涛(1986)。
(6)尽管并没有针对全国新生克汀病儿的统计数据,但许多地区性的研究都证实了克汀病患儿出生率在供应碘盐后的大幅下降。例如,朱宪彝(1981)发现,贵州东南部某公社供应碘盐前两年的克汀病患儿出生率为70%,供碘后一年内克汀病患儿出生率仅为1/60。
(7)20世纪80年代后期非碘盐的大规模冲击,使得许多病区病情严重回升。例如,1988年全国碘缺乏地区流入的非碘盐竟占碘盐需求量的1/6(何光临,1991)。
(8)我国于1994年和1995年相继实施食盐专营政策和全民食用加碘盐政策,使得非碘盐冲击问题得到显著的改观(王海潜,1994;谭洽,1996;陈吉祥等,1999;肖东楼等,2007)。
(1)如需了解有关此数据的更多信息,请登录http://css.sysu.edu.cn。
(2)目前,双重差分模型已被广泛用于对疾病防治影响的考察,具体参见Bleakley(2010)、Cutler等(2010)和Lucas(2010)的研究。
(1)高林等(1992)调查了甘肃两个乡,其中重病区乡的克汀病患病率为1.19%,亚克汀病患病率为24%;轻病区乡的克汀病患病率为0.72%,亚克汀病患病率为4%。
(2)由于图集只显示了各县市患病率所属的区间,因而我们用所属区间的中间值作为真实患病率的近似。如果克汀病患病率位于小于0.05%的区间,则近似值为0.025%;患病率位于0.05%-0.20%区间,则近似值为0.125%;患病率位于0.20%-0.50%区间,则近似值为0.35%;患病率位于0.50%-1%区间,则近似值为0.75%;患病率>1%,则近似值为1.15%。
(3)出身类型包括贫(雇)农、下中农、富裕中农、工人等13类;职业类型为第五次全国人口普查所使用的职业分类。
(1)这里的出生年份维度是分省别的,即年龄相同但省份不同的个体被设为不同的聚类。这是由于本研究的双重差分模型控制了省级固定效应与个体出生时期变量的交互项,因而模型在识别补碘影响时比较的是同一省份内部的样本。
(1)例如,包爱民等(2000)发现,6岁以后开始补碘的儿童较同年龄未补碘儿童有着更高的身高。
(1)样本中,小学毕业个体占87.58%,初中毕业个体占65.98%,高中毕业个体占23.29%。
(1)|k|表示对k取绝对值。
(2)这样,补碘开始年份4年前出生个体的区域差异被地区固定效应吸收,无需额外控制。
(1)CLDS调查仅对过去一年内有工作的个体询问年收入情况,因而未工作个体的年收入变量为缺失值。