Population censuses and sample surveys as a source of fertility statistics

1. Population censuses and sample surveys as a source of fertility statistics

2. Methods used for fertility statistics Birth histories Reverse survival Fertility statistics The own-child Recent births Birth history reconstruction Children ever born

3. Reverse survival – the rational • Number of births in the population during the year prior to the census = population under 1 year of age in the census * reverse survival factor • Reverse survival – adjustment for mortality (persons died before the census was taken) • If no complete civil registration data, reverse survival can be used to estimate the following for 15 years prior to census (some surveys): • Number of births • Crude birth rates • General fertility rates • Assumption: No migration! (or can be neglected)

4. Reverse survival - Information needed • Age – by single years • Better if collected as date of birth • Level of mortality, can be obtained from • Children ever-born and surviving (for estimated life tables) • Total number of persons in a year (for crude birth rate) • Number of reproductive age women (general fertility rate)

5. Reverse survival - Estimation • Total number of births x years before the census = population x year of age in the census * reverse survival factor

6. Reverse survival - tabulation • Population by single years of age

7. Reverse survival - quality • The quality of reverse survival estimates of births and birth rates depends on the accuracy of • Age distribution (most important) • Reverse survival factors • Extend of migration (may be important to small areas) • Assessment of quality: compare estimates from different sources at different times

8. The own-children method the rational • Match the children reverse-survived with their mother  disaggregate reverse-survived births by age and/or other characteristics of mother • Any person under age 15  child • Note: biological children only

9. The own-children method - information needed • Age, by single years • Is mother of the child alive and living in the same household? • If yes, which person is the mother? • Line number of the mother (for this child) OR • Relation to head of household (applies for nuclear households or similar types)

10. The own-children method - tabulation

11. The own-children method - estimation • Age specific birth rate 10-15 years preceding a census or survey

12. The own-children method - quality • The quality of own-children estimates of age-specific fertility rates depends on the accuracy of • The quality of matching! • Age distribution (more important if age exaggeration) • Reverse survival factors • Extend of migration (may be important to small areas)

13. Birth history reconstruction – the rational • Own-children methods: • If number of own-children = number of children ever-born  birth history • If number of own-children < number of children ever-born  some children live elsewhere or died • Birth history reconstruction: • Imputes years of births for surviving children living elsewhere and deceased children

14. Birth history reconstruction- information needed • Age, by single years • Identify mother (line number or relation to the household head) • Number of children ever born • Number of surviving children

15. Birth history reconstruction- Tabulation (age-parity)

16. Birth history reconstruction- Tabulation (parity-duration)

17. Birth history reconstruction-estimation • Age-parity-specific birth rates (all women at certain age) • Birth rates specific for parity and duration in parity

18. Birth history reconstruction- quality • Additional quality concerns: • Imputation of dates of birth for non-own and deceased children • If level of mortality is low and most children under age 15 lives in the same household as their mother, the influence of imputation is minimum.

19. Children ever born – some background • Widely used for over 50 years (although still a lot of problems) • Important for countries do not have complete birth registration • Also important for countries with complete birth registration • Provide fertility measures on birth order and parity of women • Study fertility by socio-economic characteristics

20. Children ever born- information needed • How many children has [this woman] had in her lifetime? • incl. all live births • Could be elaborated into a number of questions • Asked to all women • Sex of the child  sex ratio at birth

21. Children ever born- tabulation

22. Children ever born- tabulation • A few important issues: • Do not group the numbers of children, except the last open category • Distinguish children ever born not stated from no children

23. Children ever born- estimation • Parity distribution • Parity progression ratios • Average number of children ever born • Completed fertility • Total fertility rates • Age-specific birth rates

24. Children ever born- quality • Underreporting of children ever born • More serious for older women • Can use certain adjustment to fix • Failure to record childless • Proportion of childless women too low and average number of children born too high. • Still a serious problem in many countries • Selection error • Use women enumerated in census/survey to represent past experience – not a big problem though

25. Recent births- information needed • Did [this woman] have any live birth during the past 12 months (if multiple, indicate number)? OR • What was the year and month of your most recent birth OR • Have there been any live births in this household during the last 12 months?

26. Recent births- tabulations Question 1 and 3: Question 2:

27. Recent births- estimation • The questions are subject to under-reporting of births – certain adjustment is needed • Age of women during the census to be adjusted to age at giving birth

28. Recent births- quality • Reporting errors: • Poor performance of fieldworkers • “reference period error”: uncertain of the date of birth vs the reference period • Reluctant to report • Selection errors: • Excluded women had a birth recently but died before the census • Excluded household had a birth recently but dissolved before the census • Not significant in most cases, however could become an issue when many deaths occurred in a short period (HIV/AIDS)

29. Birth histories – some background • An important source on infant and child mortality • Include many questions, limited to 5000 or 10000 women • WFS or DHS • Age-specific birth rates or mortality rates

30. Birth histories – information needed • Birth history of a woman: • All children she has had • Living or deceased? • Characteristics of the children: • Sex • Date of birth • Type of birth (single, twin etc)

31. Birth histories – quality • Reporting errors

32. Conclusion • Methods are available when complete civil registration system does not exist. Civil registration, however, is still the best source. • Can also be used to evaluate the quality of civil registration data • Quality concerns

33. References: • Handbook on the Collection of Fertility and Mortality Data, United Nations (2003) • Manual X Indirect Techniques for Demographic Estimation, United Nations (1983)

34. Example – Romania Source: United Nations Demographic Yearbook

35. Example - Bahrain Source: United Nations Demographic Yearbook

36. Example - Kazakhstan Source: United Nations Demographic Yearbook

37. Data availability - children ever born* Source: United Nations Demographic Yearbook