Age-Specific Wanted Fertility Rate (ASWFR) and Total Wanted Fertility Rate (TWFR): Based on Age-Period Rates
Coverage:
Population base: All women age 15-49 years in seven five-year age groups (15-19, 20-24, 25-29, 30-34, 35-39, 40-44, 45-49 years) (IR file)
Time period: Three years preceding the survey
Numerator: Number of wanted births that occurred in a period (typically the 1-36 months before the survey) to women in the age group at the time of the birth (v008 - b3 in 1:36) (BR file)
Denominator: Number of women-years of exposure in the same period (1-36 months before the survey) of women in the age group (IR file)
The age-specific wanted fertility rates (ASFWRs) is calculated as the quotient of the numerator divided by the denominator for each age group, multiplied by 1000. The ASWFRs are an average rate over the 36-month period, expressed as an annual rate per 1000 women.
The total wanted fertility rate (TWFR) is the sum of the seven age-specific wanted fertility rates multiplied by five and divided by 1000.
Numerator: Births are tabulated according to period of birth, age of mother at the time of the birth, and wantedness of the birth.
Period of birth: The period of birth is calculated as the difference in months between the date of interview and the date of birth, both in century month code format (CDC). Births are included in the tabulation if they occur 1 to 36 months before the survey (v008 - b3 in 1:36).
Age of mother at the time of the birth: The difference in months between the date of birth of the child and the date of birth of the mother, both in CMC. The difference is then divided by 60 and truncated to whole numbers to form the age groups (agegroup = int( (b3 - v011) /60) ). Note that age group 15-19 is classified as age group 3 here, not age group 1. Births are tabulated by age group.
Wantedness: A birth is considered wanted if the number of living children at the time of conception of the birth is less than the ideal number of children as reported by the respondent. Special responses such “don’t know” (98), “up to God” (95), or other non-numeric responses (96) for the ideal number of children are assumed to be a high ideal number of children and are included in the numerator (number of living children at the time of conception < v613, if v613 <= 98).
For the calculation of the time of conception, nine months are subtracted from the date of birth. A preceding child is considered living at the time of conception if it was born before the date of conception and a) is living at the time of the survey or b) died at or before the date of conception (calculations based on century month codes). The date of death of preceding children who died is calculated by adding the age at death in months to the child’s birth date in century month code. If a child’s age at death is reported in years, then the child is assumed to have died at ages 6 months higher than the number of years (30 months for children who died at 2 years of age, 42 months for children who died at 3 years of age, etc.).
Variables: BR file.
|
b3 |
CMC date of birth of child |
|
b5 |
Child is alive |
|
b6 |
Age at death |
|
b7 |
Age at death (imputed) |
|
v613 |
Ideal number of children |
|
v011 |
CMC date of birth of respondent |
|
v008 |
CMC date of interview |
|
v005 |
Woman’s individual sample weight |
Denominator: Women-years of exposure are calculated as the sum of the number of months exposed in the five-year age group during the time period divided by 12. A woman can contribute exposure to several age groups in the period, depending on the length of the period. For periods exceeding five years a woman can contribute to more than two age groups. For a period of three years or five years a women will contribute to no more than two five-year age groups during the 36- or 59-month period. The description below assumes a period of 1-36 months preceding the survey, and that a woman contributes to at most two age groups, described here as the higher age group and the lower age group:
Higher age group: A woman’s age at the end of the period determines the higher age group. The higher age group is calculated by subtracting the women’s date of birth from the date of interview minus one (in CMC), dividing the difference by 60 and truncating to a whole number (agegroup = int( (v008-1-v011)/60 ). The -1 is to ignore the month of interview and use just the 36 months prior to but not including the month of interview.
The number of months spent in the higher age group is the difference in months between her age at the end of the period of exposure (date of interview less one month) and the lower age limit of the age group plus one month (exposure = v008-1-v011 - agegroup*60 + 1). As the -1 and the +1 cancel out this can be simplified to (exposure = v008-v011 - agegroup*60). If the number of months in the age group exceeds 36 then the exposure is truncated to 36 for the period (exposure = 36 if exposure > 36). If the number of months in the age group is less than the duration of the time period (36 months), then the woman contributes exposure to both the higher age group and the next lower age group (agegroup-1).
Lower age group: The contribution to the lower age group is 36 less the number of months of exposure in the higher age group. If the number of months in the higher age group is greater than or equal to the duration of the time period (i.e., >=36 months), then the exposure in the higher group is the duration of the period (36 months) and the exposure in the lower age group is zero.
Tabulation: Each woman is tallied twice, once according to her higher age group accumulating the exposure she contributes to that group and once in the lower age group accumulating lower age group exposure. For samples of ever-married women, the exposure is adjusted to represent all women by multiplying the exposure by the woman’s “all women factor” (awfactt), which is derived from the proportion of women ever-married from the persons data file (PR file). See the section on All Women Factors for details on their calculation. The total exposure in each age group is then the sum of the exposure in each age group from the first and second tallying.
Variables: IR file.
|
v011 |
CMC date of birth of respondent |
|
v008 |
CMC date of interview |
|
v005 |
Woman’s individual sample weight |
|
awfactt |
All women factor (only needed with ever-married samples) |
See the Age-Specific Fertility Rates (ASFRs) for examples of the calculation of the denominators.
The total number of children to which a woman has given birth is recorded obligatorily by the interviewer; no unknown numbers of children are allowed. There are six values involved in the calculation of ASWFR: interview date, birth date of woman, birth dates of children, survival of children, ages at death of dead children, and ideal number of children. The interview date is always known from fieldwork dates. If missing or unknown, the birth dates of interviewed women and her children are imputed before the formation of the standard recode file. For dead children with missing age at death, the age at death in months is imputed in the standard recode dataset, using a hot deck technique based on birth order. See Date Variables in Chapter 1.
For ideal number of children, non-numeric and “don’t know” responses are considered to be high numbers, so that all births are considered wanted. Births to women with missing information on ideal number of children are considered as unwanted.
The calculation of age-specific and total wanted fertility rates is the same as age-specific and total fertility rates with the addition of the classification of births to wanted or unwanted at the time of conception.
Births to women younger than 15 years or older than 49 years at the time of the birth are not included.
Births in the month of interview are excluded. This exclusion is because this month does not represent a full month but is censored by the date of interview.
A three-year (36 month) time period is taken for calculating current AFSR. This period is a compromise between the need for recency and reduction of sampling variation. This time period was selected during the World Fertility Survey, when sample sizes were on average about 5,000 women. For comparability over time and across surveys, this period has been maintained by The DHS Program.
No adjustment is made for truncation by age. Women who are at most 49 years at the time of interview were 48 years the year before and 47 years two years before the interview. The reason no adjustment is made is that the tiny probability of women age 48 and 49 years of age giving birth in the three years preceding the survey outweighs the complication of adjusting by single years of age.
In line with general DHS policy, no adjustment is made for possible omission or date misreporting of the dates of birth of children or misreporting of the date of birth of the woman.
For samples of ever-married women, it is assumed that never-married women have not had any births. Only the denominator of the rates is adjusted to estimate the number of all women.
Bankole, A. and C. F. Westoff. 1995. Childbearing attitudes and intentions. DHS Comparative Studies No. 17. Calverton, Maryland, USA: Macro International. https://dhsprogram.com/publications/publication-CS17-Comparative-Reports.cfm
Bongaarts, J. 1990. The Measurement of Unwanted Fertility. Working Papers, No. 10. New York: Population Council.
Croft, T. 1991. Date Editing and Imputation. Demographic and Health Surveys World Conference Proceedings, II: 1337-1356, Columbia, Maryland: IRD/ORC Macro. https://dhsprogram.com/publications/publication-dhsg3-dhs-questionnaires-and-manuals.cfm
Lightbourne, R.E. 1985. “Desired Number of Births and Prospects for Fertility Decline in 40 Countries.” International Family Planning Perspectives 11(2):34-47.
Lightbourne, R. 1987. Reproductive Preferences and Behaviour. In The World Fertility Survey: An Assessment, ed. John Cleland and Chris Scott, 836-861. London: Oxford University Press.
Measure Evaluation Family Planning and Reproductive Health Indicators Database
Westoff, C. F. 1991. Reproductive preferences: a comparative view. DHS Comparative Studies No. 3. Columbia, Maryland, USA: Institute for Resource Development. https://dhsprogram.com/publications/publication-CS3-Comparative-Reports.cfm
DHS-8 Tabulation plan: Table 6.6
API Indicator IDs:
PR_WTFR_W_WFR