The standardization or decomposition approach is suitable where the overall fertility decline has rested largely upon the marital fertility components, and where contraceptive use rested largely upon programme supply (Ross and Lloyd, 1992:350. The standardization approach measures changes in the general fertility rates, the crude birth rate or total fertility rate of a specified population. Since these rates are composite rates, it is necessary to decompose them in order to ascertain what part of the change is achieved by various demographic parameters and what part results from actual changes in fertility. Through this method the changes in crude birth rates and total fertility rates in Pakistan over the past two decades, that is, from 1965 to 1985, were decomposed.
The decomposition of the crude birth rate into its four components follows the United Nations (1979:7-33) method. Accordingly, the crude birth rate can be decomposed into its components as follows:
CBR = GFR . W/P = (LAiMi.Fi)W/P i
where CBR = Crude birth rate. GFR = General fertility rate;
W/P = Proportion of female population of reproductive ages 15-49 years out of total population;
i = Age group;
Ai = Age distribution of females in age group i among women of reproductive ages.
Mi = Proportion of married women in each five-year age group of the female population aged 15-49 years; Fi = Marital fertility rates in each five year age
group of the female population aged 15-49 years.
The absolute difference between the crude birth rates corresponding to the years 1965, 1975 and 1985 is attributed to the changes occurring during that period in (a) the proportion of female population of reproductive ages in the total population; (b) the marital status distribution of females; (c) the age structure of female population of reproductive ages; and (d) the marital fertility rates. The effect of changes in each of these four factors on changes in the crude birth rate is additive, and thus, the effect of each factor is treated separately. The assumption underlying the evaluation of the effect of one factor is that each of the other factors remains constant in the base year. The formulae for comparing the contribution of each of the four components of the crude birth rate are as follows:
Age structure = W l/Pl L(A2j-Alj) M lj.Flj i
Marital structure = W l/Pl EA1 j (M2j-Mlj) F lj i
Marital fertility = W l/Pl ZAlj.M lj (F2i-F li) i
Proportion of women in the reproductive ages 15-49 years to
total population = (W2/P2-W1/P1) ZA lj.M li.Flj i
where subscripts 1 and 2 refer to the beginning and end periods of the changes examined respectively.
The data used in the standardization approach are based on the three National Demographic Surveys undertaken in Pakistan during the periods 1962-65, 1974-75 and 1984-85. As the national Family Planning Programme was launched during 1965, data from the Population Growth Estimation Survey for the period 1963-1965 were considered appropriate for the initial (base) year of the standardization. The data for the mid-period 1975 and the end period 1985 have been obtained from the Pakistan Fertility Survey 1975 and Pakistan Contraceptive Prevalence Survey 1984-85 respectively. Data for the computation of the components of the crude birth rate for these periods are compiled in Appendix 5.4.
A consistency test for all data sets was applied to determine compatibility between the crude birth rate and its four components. These tests reveal that the crude birth rate for all periods, derived from the components, compares very closely with those derived directly from the data itself (Appendix 5.5). The consistency test applied, therefore, suggests the appropriateness of the crude birth rate for standardization purposes.
Due to changes in age structure, marital structure, and marital fertility, the results of the decomposition of changes in general fertility rate are separately calculated for each age group and overall changes in the crude birth rate are calculated from its relation with gross reproduction rate for the period 1965-75, 1975-85 and 1965-85 as given in Appendix 5.6. Analysis of results of Appendix 5.6 shows that because of more changes in the combined contributions of age structure, marital structure and marital fertility, the decline in the general fertility rate and the crude birth rate has been greater during the 1965-75 period, compared to the 1975-85 period. The decomposition of changes in the crude birth rate for the period 1965-75, 1975-85 and 1965-85 due to changes in age structure, marital structure, marital fertility and proportion of women of reproductive age is summarized in Table 5.5. It is evident that the largest share of the decline in the crude birth rate is explained by the changes in marital fertility in all the
periods, followed by changes in marital structure. Marital fertility explained 56 per cent of the decline during the period 1965-75 and 72 per cent during the period 1975-85. Changes in marital structure were also important for the decline in the birth rate accounting for about one-third of the total change. Overall, the four factors in the model for the period 1965-1975 and for the period 1975-1985 jointly explained 98 per cent and 92 per cent of the decline in the crude birth rate respectively.
Table 5.5: Decomposition of changes in the crude birth rate, Pakistan, 1965-85
Change accounted for by Absolute change
per 1,000
Relative change per 1,000
Age structure
Period: 1965-75 with base year 1965
-0.919 -15.420 Marital structure -1.881 -31.560 Marital fertility -3.326 -55.805 PWRA* +0.299 +5.017 Change explained -5.827 -97.768 Change observed -5.960 100.000 Interaction -0.133 -2.232 Age structure
Period: 1975-85 with base year 1975
+0.673 + 17.081 Marital structure -1.490 -37.817 Marital fertility -2.819 -71.548 PWRA* +0.013 +0.330 Change explained -3.623 -91.954 Change observed -3.940 100.000 Interaction -0.317 -8.046 Age structure
Period: 1965-85 with base year 1965
-0.516 -5.212 Marital structure -4.277 -43.202 Marital fertility -6.848 -69.172 PWRA* +0.314 +3.172 Change explained -11.327 -114.414 Change observed -9.900 100.000 Interaction +1.427 +14.414
Note: * -Proportion of women of reproductive age. Source: Calculated from Appendix 5.6
Finally, through the standardization approach, the number of births averted by changes occurring in the crude birth rate due to changes in the four factors contained in the model have been estimated (Table 5.6). Births averted during 1975 due to change factors of the period 1965-75 amount to 421068 and more than half (56 per cent) of
Births Averted
Change Factors Number Percentage
(A ) B ir th s a v erted in 1975 du e to c h a n g e fa c to r s o f 1965-75
Age structure 64929 (-15.4)
Marital structure 132889 (-31.6)
Marital fertility 234977 (-55.8)
Proportion of women of reproductive age -21125 (+5.0)
Birth averted due to above factors 411670 (-97.8)
Births adjusted for interaction 9398 (-2.2)
Total births averted 421068 (100.0)
(B) B irth s a v e rted in 1985 due to c h a n g e fa cto rs o f 1975-85
Age structure -63931 (+17.1)
Marital structure 141543 (-37.8)
Marital fertility 267792 (-71.6)
Proportion of women of reproductive age -1235 (+0.3)
Births averted due to above factors 344168 (-92.0)
Births adjusted for interaction 30115 (-8.0)
Total births averted 374283 (100.0)
(C ) B irth s a v erted in 1985 du e to c h a n g e fa ctors o f 1965-85
Age structure 49017 (-5.2)
Marital structure 406296 (-43.2)
Marital fertility 650533 (-69.2)
Proportion of women of reproductive age -29831 (+3.2)
Births averted due to above factors 1076015 (-114.4)
Births adjusted for interaction 135558 (+14.4)
Total births averted 940457 (100.0)
Note: The assumptions considered for births averted during different periods were: (A) For births averted in 1975 due to change factors of the period 1965-75: (i) Crude birth rate (CBR) in 1965 = 46.46 per 1000; (ii) Hypothetical CBR in 1975 = 46.46 per 1000; (iii) Total population in 1975 = 70649000; (iv) Hypothetical births in 1975 = 3282353; (v) Actual births in 1975 (CBR 40.5) = 2861285; (vi) Hypothetical births averted in 1975 = 421068.
(B) For births averted in 1985 due to change factors of the period 1975-85: (i) CBR 1975 = 40.5 per 1000; (ii) Hypothetical CBR 1985 = 40.5 per 1000; (iii) Total population in 1985 = 94995718; (iv) Hypothetical births in 1985 = 3847327; (v) Actual births in 1985 (CBR 36.56) = 3473044; (vi)
Hypothetical births averted in 1985 = 374283.
(C) For births averted in 1985 due to change factors of the period 1965-85: (i) CBR 1965 = 46.46 per 1000; (ii) Hypothetical CBR 1985 =46.46 per 1000; (iii) Total population in 1985 = 94995718; (iv) Hypothetical births in 1985 = 4413501; (v) Actual births in 1985 (CBR 36.56) = 3473044; (vi) Hypothetical births averted in 1985 = 940457.
Source: Calculated from Appendix 5.6
these have been due to changes occurring in marital fertility. Births averted during 1985, on account of change factors of the period 1975-85, amount to 374283 indicating a decline of 46785 (421068-374283) births averted in 1985 compared to 1975.
However, during this period, the marital fertility even contributed to a substantial decline (72 per cent) in births averted compared to other factors. The decline in fertility due to changes in marital fertility decline may have accounted for the family planning programme effect.
Marital structure and marital fertility are related to policy measures such as the minimum age at marriage or the family planning programme. Therefore, the decomposition of the total fertility rate (TFR) into marital structure and marital fertility is carried out using the technique originally developed by Kitagawa (1955) and subsequently adapted by Retherford and Ogawa (1978). The total fertility rate can be written as follows:
TFR = 5 I F j ; Also, TFR = 5SMi.Fi
i i
where TFR = total fertility rate; Fi = marital fertility; Mi = marital structure; i = age group.
The changes in TFR can then be decomposed into components according to the formula indicated by Retherford and Ogawa (1978) as follows:
A TFR = 5SFpA + 5XM{A
where A denotes changes and Fi and Mi are average values
of marital fertility and marital structure respectively over the period, obtained by summing the beginning and end values and dividing by two.
From the above equation a sum of two components of change in TFRs is obtained: the first on the right hand side of the equation is the contribution of the changes in the TFR due to changes in marital structure and the second indicates the changes in the TFR due to changes in marital fertility. Each of the two components can also be broken down by five-year age groups. The advantage of this method is that the
observed changes in the TFR are fully explained by the changes in marital structure and marital fertility.
Table 5.7: Decomposition of changes in total fertility rate, Pakistan 1965-1985
Components 15-19 20-24 Age Groups 25-29 30-34 35-39 40-44 45-49 15-49 1965-1975 Marital structure 0.02 -0.32 -0.15 -0.08 -0.01 0.03 0.01 -0.41 Marital fertility -0.51 0.26 0.11 0.43 -0.11 -0.05 -0.48 -0.29 Total -0.49 -0.06 -0.04 -0.35 -0.12 -0.02 -0.47 -0.70 TFR 1965 =7.00, TFR 1975 = 6.30 1975-85 Marital structure -0.32 -0.15 0.09 0.06 0.05 0.05 0.02 -0.12 Marital fertility -0.04 -0.28 -0.61 -0.35 0.01 0.29 0.61 -0.23 Total -0.36 -0.43 -0.52 -0.29 0.06 0.34 0.63 -0.35 TFR 1975 = 6.30, TFR 1985 = 5.95 1965-85 Marital structure -0.39 -0.45 -0.05 -0.01 0.04 0.09 0.06 -0.32 Marital fertility -0.47 -0.05 -0.52 -0.80 -0.10 0.23 0.11 -0.73 Total -0.86 -0.50 -0.57 -0.81 -0.06 0.32 0.17 -1.05 TFR 1965 =: 7.00, TFR 1985 = 5.95
Source: Rukanuddin et al., 1985; Population Planning Council of Pakistan, 1976; Population Welfare Division, 1986.
The results of the decomposition of the age specific and total fertility rate, which is a function of marital structure and marital fertility, are presented in Table 5.7. It is evident that in Pakistan a decline of about one child per woman has occurred over the last two decades. The magnitude of decline in fertility was more visible for the 1965- 1975 period (0.7), compared to the 1975-1985 period (0.4). A substantial decline, about 60 per cent, in fertility during 1965-75 period has occurred because of the changes in marital structure. One explanation for this could be the legal restriction on minimum age at marriage (16 for females and 18 for males) imposed in Pakistan by the Government for the first time in the early 1960s. During 1975-85, the marginal decline
in fertility has occurred mainly because of marital fertility compared to marital structure.