Demographic and Health Surveys Methodology - Measure DHS

Statistics: Median Age at First BirthDefinitionMedian age in years at birth of first child.A. Coverage: Women of all marital statuses.B. Median: Interpolated calculated median.CalculationA. Age at first birth: Difference between birth date of first-born child and birth date of woman (inCMC format), truncated to single years of age.B. Numerators: Number of women within single age group categories. Women with no births areincluded in a separate category.C. Denominator is the number of women of all marital statuses. Ever-married samples denominatorsare adjusted by the all women factors.D. Numerators for each age group category are divided by the same denominator and multiplied by100 to obtain percentages.E. Medians are calculated from cumulated single year of age percent distributions of age at firstbirth. Median is linearly interpolated between the age values by which 50 percent or more of thewomen had a first birth.Handling of Missing ValuesNot applicable—Birth dates of children are imputed if missing; therefore birth dates do not have missingvalues.Notes and Considerations1. Since the difference in mother’s and child’s birth dates are truncated to years, differencebetween them is taken as including up to next completed year of age (cumulated percentagefor women with a difference of 19 years actually includes all women below 20 years of age atfirst birth). Therefore an adjustment is made to the interpolated median by increasing theinterpolated value by one year.2. Since the median is based on all women including those without a birth, there may not be amedian for younger cohorts of women (since fewer than 50 percent of the cohort may havehad a birth).Guide to DHS Statistics 39 Updated September 2006