Measures of Fertility

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No. Bio_Stat - 6 Date: 07.09.2008 MEASURES OF FERTILITY Lecture Series on Biostatistics Dr. Bijaya Bhusan Nanda, M. Sc (Gold Medalist) Ph. D. (Stat.) Topper Orissa Statistics & Economics Services, 1988


CONTENTS Introduction Uses of Fertility data Sources of Fertility data Measures of Fertility Crude Birth Rate (CBR) General Fertility Rate (GFR) General Marital fertility Rate (GMFR) Age Specific Fertility Rate (ASFR) Total Fertility Rate (TFR) Gross Reproduction Rate (GRR) Net Reproduction Rate (NRR)


LEARNING OBJECTIVE They will be able to compute different indices of fertility. They will be able to spell out general determinants of fertility. They will be able to spell out usefulness of fertility indicators.

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Fecundity : The physiological capacity of women to reproduce . Fertility : In demography, it is the actual birth performance of a group of women or to the relative frequency with which the birth occurs in total population or in the population exposed to it. This is the Result of fecundity INTRODUCTION

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Importance Fertility behavior of a given time gives shape to the future age-sex structure Hence, studying the fertility behavior has an implication on the overall welfare planning process Produce the alterations in the size of a population Sources of Data : There are three sources: Registration of vital events Sample Registration System (SRS) National family health surveys (NFHS)


Quantify the birth performance of a population over a period of time. Used to compare the fertility levels of a number of population, during a particular time interval Exhibit a time trend in fertility in a population in the study of differential fertility by various socio-economic, racial and ethnic groups. MEASURES OF FERTILITY Uses:

Crude Birth Rate (CBR):

Crude Birth Rate (CBR) Ratio of the total number of live birth to the average population ever lived during a given year and geographical area. Where B = Total No. of live births in a given year & area. P= Mid year population of the year B P × 1000 Crude Birth rate =

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Merits Requires minimum data on fertility Easy to interpret Demerits Cannot be used to compare the levels of fertility for any two populations because they may differ widely in their age-sex composition. It is not a fertility rate as it includes all the population either exposed or not exposed to the risk of child bearing.

General Fertility Rate (GFR):

General Fertility Rate (GFR) Simplest measure of fertility Defined as the number of births per year per thousand mid-year woman of the child bearing ages. W 15-49 = total number of women of child bearing age 15-49 at the mid point of the year in a given geographical area. GFR = B W 15-49 × 1000

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Advantages: It includes the female population in their reproductive ages who are supposed to be exposed to the risk of giving birth. Generally used in population projection using component projection method.

General Marital fertility Rate (GMFR):

General Marital fertility Rate (GMFR) Overall measure of fertility of married women. It is the number of births per year per thousand mid- year married women within reproductive ages. Symbolically, W m 15-49 = total no. of married women of child bearing age 15-49 at the mid-point of the year GMFR = B W m 15-49 × 1000

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Age pattern of child bearing in any population is the best revealed by computing age specific fertility rates. It is the number of births per year per women in a given age group in a given year and geographical area. n B x = No. of Births to the women of ages x to x + n yrs in a given yr and area. n W x = No. of women aged x and x + n years at mid-year in a given year and area n is usually taken as 5 years. Age Specific Fertility Rate (ASFR) ASFR( n f x ) = n B x n W x

Age Specific Marital Fertility Rate(ASMFR):

Age Specific Marital Fertility Rate(ASMFR) Measured as the ratio of no. of births per year in a given age group to the total no. of married women in that age group at mid-year. n W m x = no. of women aged x to x + n years at mid-year in a given year and area n B x = no. of births in a yr to the married women of ages x to x+n yrs in a given yrs and area n M x = proportion of married women at ages x to x+n = ASMFR ( n g x ) = n B x n W m x n f x n M x

Total Marital Fertility Rate (TMFR):

Total Marital Fertility Rate (TMFR) An over all summary measure of marital fertility, Obtained by summing the age- specific marital fertility rate for each age of the child bearing span. for x= 15,20.25…40 In this case n=5 TMFR = 5 × ∑ x 5 g x

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Number of children which a women of hypothetical cohort would bear during her life time if she were to bear children through out her life at the age-specific fertility rates for given year and if none of them dies before crossing the age of reproduction. for single year ASFR. for 5year ASFR. For x = 15, 20, 25.…… In this case n=5 Total Fertility Rate (TFR) TFR = ∑f x X TFR = 5 × ∑ 5 f x X

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Indicates the number of daughters of a hypothetical cohort of women by the end of the reproductive life if she bears the births according to a given schedule of age-specific fertility rates( taking only female births) without experiencing any mortality till the end of reproductive life . 5 B f x = no. of female births to women aged x to x + 5. Limitation of GRR: It dose not consider the mortality of the cohort of women. Gross Reproduction Rate (GRR): Measure of population replacement GRR= 5 ∑ x=15 5 W x 5 B f x GRR f B B  TFR , f B B No. of female Births Total No. of Births = ~ =

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NRR is GRR adjusted for mortality schedule of cohort of women Number of daughter that would be born to a cohort of women during their lifetime if they experience a fixed scheduled of ASFR and ASMR , therefore, Net Reproduction Rate (NRR): NRR = 5 ∑ x=15 n B x × 5 W x f 5 Π x f 5 Π x = survival rate = Mean size of the cohort of women of age x to x+5 Initial size of the cohort

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( Continued……….) Replacement Level Fertility: Women replace with their offspring This is the level of fertility that gives NRR=1. Generally takes the value, the total fertility rate of level 2.1 children per women in a population. It is the precondition for population stabilization (process to achieve zero growth of population)

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Children Surviving (CS) Total number of children , which a women has born as live births and they are still live. Children Ever Born (CEB) It is a cohort measure It is the total number of children a women has born till the date. Also include those children , which a women has born as live births but they died at any time later. Parity Number of birth a women has given

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Exercise: The following table gives the population of a country for the year 1951, together with the estimated numbers of births and deaths based on a special vital statistics enquiry conducted in the country. Calculate 1. Crude death rate for the total population and for males and females. 2. Crude birth rate for the total population, 3. General fertility rate, 4. Total fertility rate, 5. Gross reproduction rate, and 6. Net reproduction rate.

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Age Males Females Births Survival Rates Population Deaths Population Deaths Males Females 0 - 04 442532 18623 434980 17308 05 - 09 419042 1809 416736 1709 10 - 14 393543 984 384616 1638 15 -19 308269 1233 314056 1329 3578 3343 0.914 20 -24 257852 1289 269340 1481 7293 6690 0.899 25 - 29 230629 1776 236187 1677 6775 6361 0.844 30 - 34 204188 1633 203477 1465 4233 4187 0.868 35 - 39 182270 1588 176534 1289 2999 2685 0.852 40 - 44 162509 1967 145037 1233 593 725 0.834 45 - 49 128784 2138 122949 1352 129 128 0.819 50 - 54 102971 1905 96589 1188 55 - 59 80717 2478 78311 1605 60 - 64 58899 3099 58142 1980 65 - 69 37797 2428 39099 2468 70+ 45099 5981 48866 7175

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