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    Forschungsinstitut zur Zukunft der ArbeitInstitute for the Study of Labor

    Estimating the Effect of the One-Child Policy onSex Ratio Imbalance in China: Identifi cation Based on the Difference-in-Differences

    IZA DP No. 5149

    August 2010

    Hongbin LiJunjian YiJunsen Zhang

  • Estimating the Effect of the One-Child Policy on Sex Ratio Imbalance in China:

    Identification Based on the Difference-in-Differences

    Hongbin Li Tsinghua University

    and IZA

    Junjian Yi Chinese University of Hong Kong

    Junsen Zhang

    Chinese University of Hong Kong and IZA

    Discussion Paper No. 5149 August 2010


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  • IZA Discussion Paper No. 5149 August 2010


    Estimating the Effect of the One-Child Policy on Sex Ratio Imbalance in China:

    Identification Based on the Difference-in-Differences* In China, the male-biased sex ratio has increased significantly. Because the one-child policy only applied to the Han Chinese but not to minorities, this unique affirmative policy allows us to identify the causal effect of the one-child policy on the increase in sex ratios by a difference-in-differences (DD) estimator. Using the 1990 census, we find that the strict enforcement of the one-child policy has led to 4.4 extra boys per 100 girls in the 1980s, accounting for about 94% of the total increase in sex ratios during this period. The robust tests indicate that the estimated policy effect is not likely confounded by other omitted policy shocks or socioeconomic changes. Moreover, we conduct the DD estimation using both the 2000 census and the 2005 mini-census. Our estimates suggest that the one-child policy has resulted in about 7.0 extra boys per 100 girls for the 1991-2005 birth cohort. The effect of the one-child policy accounts for about 57% and 54% of the total increases in sex ratios for the 1990s and the 2001-2005 birth cohorts, respectively. JEL Classification: J13, J15, J18, O10 Keywords: one-child policy, sex ratio imbalance, difference-in-differences estimator Corresponding author: Junsen Zhang Department of Economics Chinese University of Hong Kong Shatin, NT Hong Kong E-mail:

    * The work described in this paper was substantially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project no. CUHK 454608).

  • 1 Introduction

    According to three recent waves of population censuses in China, the sex ratio at birth has

    drastically increased from 108.5 in 1982, to 113.8 in 1990, and to 119.9 in 2000, deviating

    far from the biologically stable range from 103 to 107 (NBS, 2002).1 Considering the far-

    reaching consequences of the persisting sex ratio imbalance on both the marriage market

    and the labor market (Angrist, 2002; Becker, 1991; Chiappori, Fortin & Lacroix, 2002; Rao,

    1993), and even on the crime market (Dreze & Khera, 2000; Edlund et al., 2008; Hudson

    & Boer, 2002),2 the problem of the male-biased sex ratio in China has drawn increasing

    attention from demographers, economists, and other social scientists (e.g., Banister, 2004;

    Coale & Banister, 1994; Hesketh & Xing, 2006; Qian, 2008; Tuljapurkar, Li & Feldman,

    1995; Zeng et al., 1993).3

    However, the cause for the increase in sex ratio has been a subject of heated debate. Oster

    (2005) raises the possibility that a biological factor, hepatitis B, accounts for about 70% of

    the "missing women" in China. The hepatitis B story is questioned by Das Gupta (2005).

    Lin & Luoh (2008) show direct micro evidence that hepatitis B does not aect the sex ratio in

    Taiwan. Oster and Chen (2008) also admit that hepatitis B does not explain male-biased sex

    ratios in China. Although the biological factor of hepatitis B seems to have been excluded

    from this "missing women" story originally discovered by Sen (1990), the debate has not

    totally resolved. Many economists and demographers argue that the one-child policy has

    been the major reason for the increase in sex ratios in China (Ebenstein, 2009; Li, 2002; Das

    Gupta, 2005; Zeng et al., 1993). Guilmoto (2009) discusses that the increase in sex ratios

    in Asia may be triggered by the progress in gender selection technology. Qian (2008) claims

    that a substantial percentage of the increase in sex ratio is attributable to the gender wage

    1The sex ratio is dened as the number of males per 100 females in the reference population.2It has also been suggested that the endogenized sex ratio by the son preference may systematically

    degenerate girls to be born in low status families (Edlund, 1999).3Porter (2007, 2008) has analyzed the eects of the male biased sex ratio on marriage, intrahousehold bar-

    gaining, and intergenerational transfers; Wei & Zhang (2008) have explored the eect of sex ratio imbalanceon saving behavior in China.


  • gap.

    This paper argues that the increase in sex ratios in China has been a result of a combina-

    tion of son preference, a decrease in fertility induced by the one-child policy, and the progress

    of gender selection technology. These elements are the three indispensable ingredients in the

    increase in sex ratios in China. Son preference is a cultural background; gender selection,

    such as gender-selective abortion, is a necessary tool through which a desired gender can be

    pursued; and the decrease in fertility induced by the one-child policy leads to increasing sex

    ratios. Given son preference and gender selection technology, the frequency or intensity of

    gender selection usage is dierent at dierent fertility levels. The increase in sex ratios is a

    manifestation of the decline in fertility caused by the one-child policy. With lower fertility

    coupled with gender selection to realize the desired gender, the impact of any factor on the

    sex ratio is higher.4

    Previous research has tried to identify the causal relationship between the one-child policy

    and the increase in sex ratio by exploiting spatial and time variations in the implementation

    of the one-child policy. For example, Ebenstein (2009) utilizes the regional and temporal

    variation in nes at provincial level for unauthorized births, and nds that higher ne regimes

    are associated with higher sex ratios but lower fertility. The spatial and time variations of the

    one-child policy, however, may be endogenous to gender selection and sex ratios in empirical


    Our paper avoids this problem by designing a dierence-in-dierences estimator based

    on an exogenous dierential treatment between the Han and minorities under the one-child

    policy. In the quasi-experiment design of the DD estimator, both the ethnic-specic het-

    4The interaction between sex preference, fertility, and sex ratio has long been noticed in the literature(Becker, 1991; Ben-Porath & Welch, 1976). Ben-Porath & Welch (1976) conjecture a possibility that parentsindirectly choose fertility to satisfy their sex preference. To test this hypothesis, however, there exists anidentication problem because the number and gender composition of children are simultaneously deter-mined. The Chinese experience may shed light on this problem because the fertility behavior there had beenexogenously targeted by the one-child policy since 1979. Therefore, identifying the eect of the one-childpolicy on sex ratio imbalance in China can help our understanding of the interaction between fertility andsex ratios in countries where son preference is prevalent.

    5It will be discussed in detail in Subsection 2.2.


  • erogeneity and the eects of socioeconomic development have been swept out. Therefore,

    the DD estimate is very clean, and we are able to rigorously identify the causal eect and

    obtained the quantitative eect of the one-child policy on sex ratio imbalance in China.

    The one-child policy stipulates that each couple is allowed only one-child. Couples are

    given birth quotas, and they are penalized for "above-quota" births. However, a unique

    feature of the one-child policy is that minority women were generally allowed to have at least

    two children whereas the Han can only have one child.6 Th