with intervals shorter than 15 months (i.e., less than six months from birth to conception of the next child) are: 1.3 times less likely to avoid anemia; 1.7 times less likely to avoid third-trimester bleeding; and 2.5 times less likely to survive childbirth.<sup>16</sup> Therefore, short spacing is found to affect maternal mortality both directly and indirectly through increased risk of anemia.

# **3 Data**

The data used in this paper are from the India National Family Health Survey (NFHS) which contains detailed information on women’s entire birth histories, birth intervals (at the child level), health indicators (for children and their mothers), domestic violence, and other demographic and socioeconomic characteristics of women and the households they live in. The NFHSs are repeated cross-sectional surveys for a representative sample of women in India.<sup>17</sup> The women sampled for individual interviews in the NFHS are aged 15–49, and I consider the sample of all those who had at least one child ever born. Moreover, I exclude women with 9 or more children ever born to reduce heterogeneity due to women with extraordinarily high fertility (the 98<sup>_th_</sup> percentile of the pooled sample of women).<sup>18</sup> I pool the three available surveys, conducted in 1992/93 (NFHS-I), 1998/99 (NFHS-II), and 2005/06 (NFHS-III).

Using the pooled NFHS birth history data, the sex ratio at birth (here defined as the fraction of male births) is 0.519 for first births and 0.521 for all births. Among women who had their first birth during the ten years before the survey the sex ratios for first and all births are 0.513 and 0.518, respectively.<sup>19</sup><sup>_,_20</sup> Figures 1 and 2 show the sex ratio at birth (for _all_ births) by birth year in the pooled dataset and separately by survey year, respectively. Pooling different survey rounds allows me to distinguish between age and cohort-specific effects. The figures show a decreasing trend of 16 see Conde-Agudelo, Rosas-Bermdez, and Kafury-Goeta (2007) for a review of medical studies on the relationship between birth spacing and maternal health.

> 17While NFHS-I and II only interviewed ever-married women, NFHS-III includes those never married. To ensure comparability, I exclude never married women from the analysis. Since I only consider women with at least one child ever born (the vast majority of whom are or have been married), the fraction of excluded women is quite small: 72 women, equivalent to 0.02% of all women interviewed in NFHS-III.

> 18Total fertility rate (TFR) in the NFHS-III is 2.7, down from 3.4 in NFHS-I. Therefore, on average, an Indian woman in NFHS-III will give birth to 2.7 children by the end of her childbearing years. The TFR is based on age-specific fertility rates during the three years preceding the survey (IIPS and Macro International, 2007).

> 19The biologically “normal” sex ratio at birth ranges from 1.03 to 1.06 (male to female births), corresponding to a fraction of male births approximately in the range of 0.507 – 0.515 (Arnold, Kishor, and Roy, 2002).

> 20Sex ratios have been found to be affected by several biological, environmental, and genetic factors (other than behavioral factors). These include improvements in maternal health status (Bhat 2002a), mother’s malnutrition (Mathews, Johnson, and Neil, 2008; Almond and Mazumder, 2011; Andersson and Bergstrom, 1998), prevalence of Hepatitis B (Oster, 2005), birth order, timing of conception, hormonal conditions (James, 1987). Some of these biological factors and how they might affect the findings of this paper are discussed in more detail in section 6.1.

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