Measures of fertility

Measures of fertility

1. Measurement of Fertility Dr Inn Kynn Khaing M.B .,B.S, MPH, MSc (Healthcare Administration) (Japan ) Lecturer, Department of Biostatistics

2. 1. Crude Birth Rate (CBR) Ratio of the total number of registered live births among residents in an area during a calendar year to the total mid-year estimated population of the same area, also multiplied by 1,000. The number of births and death are supplied by vital registration system CBR = B P x K B = total number of live birth registered during the calendar year P = total mid-year estimated population or the total population of the middle of the year i.e. as on 1 st July K = a constant usually taken as 1,000

3. 1. Crude Birth Rate (CBR) Advantages Simplest and commonest measure on fertility Easily calculated Limitations The entire population is in the denominator, whereas all members of the population do not contribute equally to births In spite of its limitation, it is widely used due to the availability of data

4. 2. General Fertility Rate (GFR) GFR avoids some of deficiencies of CBR by changing denominator from total population to number of women in the reproductive age groups usually 15 to 49 years GFR is a ratio of total yearly registered live births to the female population of “child bearing age” i.e. from 15 to 49 years GFR = No: of total registered live birth of residents in a community in a year Total female population aged 15 to 49 X 1,000

5. 2. General Fertility Rate (GFR) To restrict the denominator to potential mothers by excluding all men and large group of women not “exposed to the risk” of child bearing by reason of age A step in the direction of measuring fertility against the proper proportion of the population Can be calculated as easily as the CBR and requires only the age and sex distribution of the population Advantages : Can be computed in situation in which the registration of the births and the enumeration of the population are satisfactory but where direct evidence of births by age of parents is lacking

6. 3. Age Specific Fertility (Birth) Ratio (ASFR) One of the most important determinants of the fertility of a population is the age of the mother Refinement: overall fertility measure is obtained by distinguishing the women of the child bearing age according to their ages and similarly subdividing the births according to the ages of the mothers Age means the age of each parent at the time of birth. ASFR : maternal birth rates than paternal birth rates

7. 3. Age Specific Fertility (Birth) Ratio (ASFR) defined as the number of births to one of a specific age group per 1,000 women in that age group usually in 5 year age intervals A set of rate for 5 year age group from 10-14 to 45-49/ 15-19 to 45-49 or 15-19 to 40-44. f i = B i P i x K B = total number of live birth registered during the year to women in the age interval i P = mid-year female population in the same age group K = a constant usually taken as 1,000

8. 3. Age Specific Fertility (Birth) Ratio (ASFR) Formula for ASFR at ages 20-24 is f 20-24 = B 20-24 P 20-24 x 1,000 Age group of mothers (year) Female population Live births ASFR 15-19 2306 154 20-24 1938 429 25-29 1661 382 30-34 1520 251 35-39 1306 199 40-44 1177 77 45-49 971 13 All ages total

9. 4. Total Fertility Rate (TFR) Sum of age specific fertility rates of women over their reproductive span i.e. all ages of child-bearing period from 15 to 49 years of age as observed in a given year. TFR = ∑ B i P i x 1,000 i = 49 i = 15 B = total number of live birth registered during the year to mothers of age i where I is an interval of one year P = mid-year female population in the same age group

10. 4. Total Fertility Rate (TFR) Usual practice, subscript i represents 5 year intervals such as 15-19, 20-24,…. And 45-49 years TFR = 5 ∑ B i P i x 1,000 i = 7 i = 1 B = number of live birth registered during the year to mothers of age I where I is an interval of 5-years P = mid-year female population in the same age group

11. 5. Gross Reproduction Rate (GRR) A special case of TFR Only distinction: the numerator of GRR is based on female births instead of total births TFR measures the total number of children a cohort of women will have GRR measures the number of daughters it will have This rate is of considerable experience in demographic theory, as it shows the extent to replace themselves, as far as the fertility level is concerned GRR shows the average number of female children born to women living through the child bearing ages (i.e. 15 to 49 years), assuming no mortality

12. 5. Gross Reproduction Rate (GRR) Suppose GRR is 3. if a female child is born at that time, and survives through her child-bearing period then she will give birth to 3 female children in her turn, on the average GRR = ∑ B x f P x f x 1,000 w 1 w 2 B x f = number of female infants born to mothers of age x P x f = number of women of age x in the mid-year population w 1 and w 2 = the lower and upper limits of the child bearing period K = 1,000

13. 6. Net Reproduction Rate (NRR) This rate consists of a hypothetical cohort of women, their deaths and their female births during their child-bearing period i.e. 15 to 49 year NRR is a measure of the number of daughters that a cohort of new born girl babies will bear during their life time assuming a fixed schedule of fertility rates and a fixed set of mortality rates NRR is a measure of the extent to which a cohort of newly born girls will replace themselves under given schedule of age specific female of fertility and mortality

14. 6. Net Reproduction Rate (NRR) NRR = B x f P x f x 1,000 f x = age specific female birth rate (daughters only) at age x NRR rate 1 means exact replacement NRR above unity indicates that the population is more than replacing itself NRR below unity indicates that the population is not replacing itself NRR is always lower than GRR because it takes into account that some women die before completing their childbearing years.

15. 7. Child-women ratio Ratio of children under age 5 to women of ‘child bearing ages’ Index – a makeshift designed to furnish a measurement of fertility when birth statistics are lacking Derived entirely form the data by age in one census Serves best as a relative measure to compare the fertility performance of different section of same population, where the disturbing effects of these other factors are presumed to be smaller Disturbing effect: instead of birth, the ratio is based on survivors of previous births

16. 7. Child-women ratio Child-women = ratio No: of children under 5 or 0-4 years of age in a population No: of women of child bearing age i.e. 15-49 X 1,000

17. De-facto method of enumeration Counting of the people actually present at some moment in those places, as of midnight on the census date. Conducted synchronously over the whole area Attempts to count all persons in the actual places where they happened to be at the time of census If de- fato method of enumeration is carried out at different times, there is a danger that a person who has travelled from one place to another – may be counted twice or he may be omitted from the count together

18. De-facto method of enumeration It requires a large staff to carry out a synchronous enumeration This is justified in areas where the population is fairly dense but not justified in areas where the population is thinly distributed A much smaller staff is used to enumerate the population in the thinly populated areas who travel over a wide area and carry out the census at different times in different places In such case, de facto method cannot be used

19. De-jure method of enumeration Counting people usually or normally or permanently present in some places Non synchronous method of enumeration may last two or three months. Suitable for loosely administered and sparsely populated part of the country A person is enumerated only in the place where he or she normally resident even though he or she may not be there at the time of the enumeration

20. De-jure method of enumeration It is assumed that every person has only one normal place of residence It is attempted to reduce the errors of omission or double-counting Some errors still remain because the census idea of normal residence is not well understood and a person may be reported as the normal resident of more than one place or may be omitted altogether.

21. Thank you!