similar, indicating that past health does not seem to be associated with the sex of the first-born.<sup>43</sup> Second, this interpretation would not be compatible with a pattern in which differential incidence of anemia between women with a first-born girl or boy is not present at the time of birth and arises only some time _after_ first birth. To understand the timing of the emergence of differences in anemia status, I plot the prevalence of anemia among women by the sex of their first-born child and the time since their first birth (using Kernel-weighted local polynomial smoothing). Figure 10 shows that there is no differential incidence of anemia at the time of first birth, and that women with a first-born girl start developing anemia approximately 16 months after the birth of their daughter and that differences increase over time.<sup>44</sup> I also estimate a probit regression for the probability of being anemic on ‘first-born girl’ and its interaction with the interval of time since birth (controlling for height and other covariates). Column (1) of table 10 shows that from the time of birth until the 11<sup>_th_</sup> month there is no differential anemia status, while differences seem to develop gradually over time, though not significantly. As expected, differential incidence of anemia develops much faster among uneducated women, for which the increase becomes significant about three years after the birth of the first child. No similar pattern is found for educated women (columns (2)–(3)).

A third check explores whether there is differential incidence of anemia at the time of _each_ birth from birth order 1 to 3. This is to make sure that anemia status does not affect the sex of the child at any birth. I run a probit regression for the probability of a female birth at birth order 1 to 3 on whether the mother is anemic (and the different levels of anemia severity) restricting the dataset to women who gave birth less than a year before the time of the survey. Table 11 shows no association between anemia status and the sex of the child at any birth order.<sup>45</sup> None of these results is consistent with explanations based on biological differences.

# **6.2 Reporting bias**

Another concern is that, as they are based on self-reported retrospective information, birth histories in the NFHS might suffer from misreporting and recall bias especially in relation to births (and deaths) occurred many years before the time of the survey (Smith, 1994; Byass et al., 2007).

> 43The results of the regressions for fertility behavior are robust to the inclusion of height (including height implies restricting the sample to second and third surveys in which measurements were taken). Results shown in table A.2.

> 44The timing of emergence of anemia is consistent with higher iron requirements particularly in the third trimester of pregnancy. Iron stores are especially depleted for women who had a short interval. Therefore, women with a first-born girl (found to be more likely to have a short interval) appear to develop anemia towards the end of their second pregnancy and these anemia differences seem to persist over time.

> 45No association (from birth order 1 to 3) is found even when using other nutritional indicators such as BMI (and the two cutoffs for underweight and obesity) and shortness. This is in contrast with Andersson and Bergstrom (1998) who find that short maternal stature and obesity are independently related to low sex ratio at birth using data for 684 women from the Central African Republic.

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