Demographic and Health Surveys Methodology - Measure DHS

III. Guide to Individual StatisticsFERTILITYCURRENT FERTILITY RATESStatistics: Age-Specific Fertility Rate (ASFR) Also Known As Age-Period Fertility Rate inthe Three Years That Precede the Date of the Survey, Presented as anAnnual RateDefinitionA. Coverage: All women age 15–49 years in seven five-year age groups (15–19, 20-24, 45–49 years).B. Numerator: Number of births that occurred in the 1–36 months before the survey to women in theage group at the time of the birth.C. Denominator: Number of women-years of exposure in the 1–36 months before the survey ofwomen in the age group.D. Rate is the quotient of the numerator divided by the denominator.CalculationA. Numerator: Births are tabulated according to period of birth and the age of mother at the time ofthe birth.1. Period of birth: The period of birth is calculated as the difference in months between thedate of interview and the date of birth, both in century-month code format (CMC). Births areincluded in the tabulation if they occur 1–36 months before the survey.2. Age of mother at the time of the birth: The difference in months between the date of birthof the child and the date of birth of the mother both in CMC. The difference is then dividedby 60 and truncated to whole numbers to form the age groups. Births are tabulated by agegroup.B. Denominator: Women-years of exposure are calculated as the sum of the number of monthsexposed in the five-year age group during the time period divided by 12. A woman can contributeexposure to just two five-year age groups during the 36-month period.1. Higher age group: A woman’s age at the end of the period determines the higher age group.The high age group is calculated by subtracting the women’s date of birth from the date ofinterview minus one (in CMC), dividing the difference by 60 and truncating to a wholenumber. The number of months spent in the higher age group is the difference in monthsbetween her age at the end of the period of exposure (date of interview less one month) andthe lower age limit of the age group plus one month. If the number of months in the agegroup is less than the duration of the time period (36 months), then the woman contributesexposure to both the higher age group and the next lower age group.Guide to DHS Statistics 26 Updated September 2006