Factors affecting paternity

We have established that there is a strong association between parental education and other indicators of SES, such as family income, rooms/home, number of residents/home, etc. We have therefore used maternal and paternal education as the SES selection factors. In order to minimize loss to follow up, infants living more than 10 km from the hospital have been excluded in each town. Other exclusion criteria include twins major central nervous system defects and chromosomal abnormalities or other conditions (e.g. microcephaly, hydrocephaly) likely to profoundly affect growth or mental development. 

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