# **3. Data and Descriptive Statistics**

## **Demographic and Health Survey**

The data on child health come from two rounds of the Demographic and Health Survey (DHS) conducted in 2003 and 2008.<sup>11</sup> The DHS are nationally representative household surveys with a large sample size that contain detailed information on demographic characteristics, fertility, contraceptive use, infant and child mortality, immunization levels, use of family planning, maternal and child health, breastfeeding practices, and nutritional status of mother and young children.<sup>12</sup> Nutritional status, especially in children, has been widely and successfully assessed by anthropometric measures in both developing and developed countries (Mei and Grummer-Strawn, 2007). Thus, following the norm in the literature we proxy the health status of children with their anthropometric measures and information on recent symptoms of illness, specifically diarrhea.<sup>13</sup> Children height and weight are converted into standardized Z-scores (height-for-age and weight-forheight), using the WHO Anthro program (WHO, 2006). For each child, depending on their sex and age, the Z-score system expresses anthropometric values in terms of standard deviations below or above the median of an international reference group.<sup>14</sup> Height-for-age Z-score (HAZ) indicates chronic malnutrition and is considered a good measure of long-term health. In contrast, weight varies in the short run due to acute starvation or severe disease. Therefore, the weight-for-height Z-score (WHZ) provides a more current indicator of health status.

The Nigeria DHS samples were selected using a stratified two-stage cluster design. The 2003 DHS consist of 7,864 households in 365 clusters or villages -with 54% of them being rural villages. In contrast, the 2008 DHS had a much larger sample size consisting of 36,800 household in 886 clusters (69% in rural areas).<sup>15</sup> We restrict the sample to those born outside of urban areas because our causal factor of

> 11 There have been some concerns about the quality of household surveys in Nigeria. However, we expect that a standardized survey like the DHS, which has been used in many countries (including two previous rounds in Nigeria), would have reasonable quality controls.

> 12 The DHS has been widely used to perform indirect estimation of population dynamics, such as fertility and mortality, in those places where there is no reliable census data.

> 13 According to the protocols used by the DHS, for children younger than 60 months of age, height is measures to the nearest 0.1 centimeter. While the standing height is measured for children 24 month or older, a measuring board is used to measure child’s length when children are younger than 24 month of age. Weight is measured to the nearest 0.1 kilogram.

14 An international reference is useful since growth in height and weight of well fed, healthy children under 5 years of age from different ethnic backgrounds and different continents is reasonably similar (WHO Multicentre Growth Reference Study Group, 2006).

15 The 2003 DHS used the 1991census frame while the 2008 DHS used the 2006 census frame. There is no available information regarding the definition of a rural area in the 2006 census frame. Some observers have suggested that 13