Hill (1987) generalized the Brass Growth Balance method [1] for estimating the completeness of the reporting of deaths relative to an estimate of the population on the assumption that the population was demographically stable, to nonstable populations closed to migration. This generalization can be used where one has data on the numbers by age group from two censuses and an estimate of the number of deaths by age group between the dates of the two censuses. With the additional information from two censuses it is possible to estimate agespecific growth rates in place of the constant growth rate implied by the assumption of stability. The method still assumes, however, that the proportion of deaths reported and the completeness of the census counts is the same at all adult ages and that, apart from this, the data are accurately reported. Moreover, in its common formulation it assumes that the population is closed to migration, although the method can be adapted to accommodate migration if data are available.
In all closed populations,
, where the ‘partial birth’ rate,
, is defined as the rate at which people turn age x in the population aged x and older and the partial death rate,
, is the rate of mortality of people aged x and older. If, in this population, the deaths are underreported to the same extent at each age then
, where
is the recorded death rate for ages x and older and c is the proportion of deaths that are reported. In practice, the count of the census populations from which r(x+) is estimated may not be complete but the assumption that the undercount is the same at each age makes it possible to solve for c from the slope of the line fitted to the
and
data points. Mortality rates can then be estimated by dividing the numbers of deaths reported in each age group by c and dividing these numbers by an estimate of the population exposed to risk, to estimate the partial birth, growth and death rates. Moreover, as a byproduct of the procedure, the less complete census counts can be adjusted to be mutually consistent, although not necessarily accurate.
Before applying this method, you should investigate the quality of the data in at least the following dimensions:
If the reported deaths are for a period other than that between the censuses, the numbers that would have been reported in the intercensal period need to be estimated. If one has annual vital registration data, this adjustment involves apportioning deaths in the first and last year of the period. If one has deaths reported by households the year before the dates of each of the first and second censuses, one has to estimate the numbers of deaths by interpolating between these estimates for the intercensal period (using the Estimating deaths.xlsx [2] spreadsheet).
In applying this method, analysts must take particular care with the following.
The interpretation and estimating processes need to take into account the source of death data (vital registration, reported by households in censuses, or recorded in hospitals) as explained below. However, the biases associated with the source of death data tend to have less impact on the estimate of completeness from the Growth Balance method than on the Synthetic Extinct Generations method [3].
Although technically one could apply this method to data in single year age categories, the data one typically works with are subject to age misstatement, so in practice one usually works with data grouped into fiveyear age groups. For convenience, since most data are published in this format, the spreadsheet is set up to work with data in the standard fiveyear groupings. However, as Blacker (1988) has shown, if this grouping fails to remove the effect of digit preference, the method should be adapted to work with an alternative fiveyear grouping of ages centred on, rather than starting with, ages at which heaping occurs.
In the case where one has annual vital registration data, this adjustment involves apportioning deaths in the first and last year of the period to the parts of the year before and after the mean dates of fieldwork of the two inquiries. Unless the age pattern of deaths is changing very rapidly, this approximation will have no effect on the results.
If one lacks data on the number of deaths between the two inquiries but this interval falls between two periods for which one does have such estimates (for example, because each inquiry included a question about deaths in the household during the previous year), one can use the Estimating deaths [2] spreadsheet. This spreadsheet estimates the number of deaths between two points in time given estimates of deaths over two other periods. To use this spreadsheet, you need the number of deaths divided into fiveyear age groups for two periods (periods 1 and 2), the start and end dates for each of these periods, and the start date and end date of the period for which one wishes to estimate the number of deaths.
To estimate partial birth, death (and migration) rates one needs to cumulate the numbers in the population, and the number of deaths (and the net number of migrants) for ages x and older. Thus, in the case of the population the following equation is used:
where A is the age at the start of the open age interval.
Analogous equations are used to calculate the number of deaths aged x and older, D(x+). In the case where these are available (unlikely though this may be) analogous equations can be used to calculate the net number of migrants aged x and older, NM(x+)). Where the numbers of migrants is not known this column is set to zero (or left blank) and the method is applied taking into account this omission, as described below.
In order to estimate partial birth and death rates (and if one has data on the net numbers of migrants, migration rates) one needs to estimate the personyears of exposure. This is estimated using the following formula:
where t_{1} is the time of the first census, and t_{2} the time of the second census.
The number of people who turned x (i.e. were ‘born’ into the open age interval x+) in the population is estimated as the geometric mean of the numbers in a cohort at times t_{1} and t_{2} divided by 5, multiplied by the length of the period between the censuses, in years, using the following formula:
Step 5: Calculate partial birth and death rates, b(x+) and d(x+), and partial growth rate r(x+) corrected for migration, i(x+)
The partial birth and death rates are estimated using the following formulae:
while the partial growth rate less the partial migration rate is calculated using the following formula:
Step 6: Plot graph of b(x+)  r(x+) + nm(x+) against d(x+), and examine to decide on the range over which the line should be fitted
Start by setting the lower age to 5 and the upper age to A1, where A is the age at the start of the open interval of the data. Inspect the diagnostic plots and decide on the age interval over which the line is to be fitted. If there is greater age exaggeration in ages at death than in ages of the living the points plotted to the right (older ages) will fall progressively below the line with age. This indicates that a lower maximum age is called for – stepping down in fiveyear steps until the effect is removed. Also, if the absolute value of the residuals of the end points are too large (e.g. exceed 0.01) then the maximum age should be lowered to prevent these points unduly influencing the slope of the line. If the age exaggeration is the same in the population and the deaths then this will have no effect on the slope and hence the estimate of completeness of reporting, but the agespecific death rates will be biased downward for these ages.
If the points plotted at the younger ages (lefthand side), particularly ages 15 to 30, deviate noticeably from the straight line and one has not included any data on migration, this probably indicates that there is significant migration (unless there is age differential underenumeration). One should thus increase the lower age of the age interval used to fit the line to age 30 or 35, depending on which produces the most sensible fit to the data.
In order to estimate the completeness of reporting of deaths relative to the population, one starts by plotting b(x+)r(x+)+i(x+) against d(x+) and estimating the coefficients of the straight line fitted to these points, using orthogonal regression, as follows:
and
where b is the slope of the line and a the intercept, and the y_{i} represent the b(x+)  r(x+) + i(x+), the x_{i} represent the d(x+) and
and
represent the means of the two series, respectively.
After fitting the straight line to all the points, one inspects the plotted points relative to the line and the residuals in order to decide on the best range of ages to use to determine the completeness of reporting of deaths. How one decides this is discussed in more detail below but any residuals greater than 1 per cent in absolute value should be excluded. A line is then fitted to these points, from which new values of a and b are determined. As a general rule, it is not recommended to truncate at an age ending in zero in a population with significant digital preference.
The completeness of reporting of deaths, c, is derived from the values of a and b as follows. Since
and
We estimate c by assuming the larger of k_{1} and k_{2} equals 1. Thus if
, assume that k_{2} = 1 and hence
and if
, assume that k_{1} = 1 and hence
and
.
In order to compute mortality rates one needs first to correct the census population for relative underenumeration. This is achieved by dividing the numbers from the first census by k_{1} and the numbers from the second census by k_{2}.
Next one needs to adjust the number of deaths for incompleteness by dividing the reported number of deaths by the estimate of completeness, c.
The adjusted personyears of exposure, PYL^{a}(x,5), are estimated in the same way as before but using the population corrected for underenumeration as follows:
Next one needs to adjust the number of deaths for incompleteness by dividing the reported number of deaths by the estimate of completeness, c, and dividing this by PYL^{a}(x,5) to produce mortality rates adjusted for the incompleteness of the reporting of deaths as follows:
Note that technically one could drop the k1/k2 adjustment and still get the same estimates of the mortality rates (since the same adjustment is made to both the numerator and the denominator). However, in that case the estimate of completeness is relative to the average of the census populations ignoring the fact that one is undercounted relative to the other.
Because the agespecific rates can be quite erratic they need to be graduated (smoothed). This can be achieved by fitting a Brass relational logit function to a sexspecific standard life table which is considered to have the same shape as that generated by the mortality rates of the population being investigated.
The accompanying workbook [2] contains a spreadsheet that allows one to produce a smooth set of mortality rates by using a relational logit model fitted to the life table generated by the adjusted mortality rates. The user can choose between the standard from the General family of United Nations model life tables or one from any of the four families of Princeton model life tables. The logit transforms of these tables together with a model life table of a population experiencing an AIDS epidemic (Timæus 2004) appear in the Models sheet. This spreadsheet also allows the user to input logit transforms of an alternative life table if there is reason to assume that it has a similar pattern of adult mortality to that of the population being studied.
In order to fit the model, probabilities of people aged x dying in the next 5 years, _{5}q_{x}, are estimated from the adjusted rates of mortality as follows:
From this the life table with a radix of l_{5} = 1 is calculated as follows:
The coefficients, α and β are determined by fitting the relational logit model as follows:
where
and superscript ‘s’ designates values based on a standard life table.
The fitted life table is then generated from the standard life table using the coefficients α and β as follows:
and
The smoothed mortality rates are derived from this life table as follows:
and
where
i.e.
and ω is the age above which the life table has no more survivors.
This example uses data on the numbers of males in the population from the South African Census in 2001 and the Community Survey in 2007, on number of deaths from vital registration for the years 2001 to 2007, and on the net number of migrants estimated from the change in foreignborn counted in the two surveys, less an estimate of the number of South Africans who emigrated between the two surveys. The example appears in the GGB South Africa_males [4] workbook.
The registered deaths for the years 2001 to 2007 for South African males are given in Table 1.
Table 1 Calculation of deaths between census dates, South African males, 20012007
Age 
2001 
20022006 
2007 
Total between censuses 
04 
29,005 
186,346 
40,314 
197,912 
59 
2,118 
14,733 
2,854 
15,566 
1014 
1,745 
10,535 
2,233 
11,207 
1519 
4,470 
23,857 
4,860 
25,473 
2024 
8,931 
51,588 
10,875 
54,960 
2529 
16,834 
96,705 
18,405 
102,802 
3034 
20,892 
137,355 
28,245 
145,588 
3539 
21,068 
137,502 
29,258 
145,900 
4044 
19,322 
128,217 
26,973 
135,936 
4549 
17,881 
113,891 
24,761 
121,010 
5054 
16,883 
104,508 
22,790 
111,157 
5559 
14,544 
90,919 
21,317 
96,854 
6064 
15,097 
84,351 
17,410 
89,930 
6569 
13,011 
77,680 
17,878 
82,843 
7074 
14,035 
68,147 
13,771 
73,036 
7579 
10,846 
59,859 
12,534 
63,871 
8084 
9,161 
44,986 
8,872 
48,163 
85+ 
7,602 
43,233 
10,009 
46,196 
The reference time for the census in 2001 was midnight between 9 and 10 October 2001. The Community Survey took place over a number of weeks in February so we can assume a reference time of midnight between 14 and 15 February 2007. Thus, if we assume deaths occur uniformly over the respective calendar years, we can apportion the deaths in 2001 and in 2007 and add these to the total for the years 2002 to 2006 to get the total number of deaths between the two estimates of the population. For example, for the age group 2024 the number is calculated as follows:
Step 2: Cumulate population, deaths and migrants downwards
One accumulates the numbers in the population, deaths and migrants from the oldest age downwards (Table 2).
Table 2 Calculation of the cumulated populations, deaths and migrants, South African males, 20012007
Age 
_{5}N_{x}(t_{1}) 
_{5}N_{x}(t_{2}) 
_{5}D_{x} 
_{5}NM_{x} 
P1(x+) 
P2(x+) 
D(x+) 
NM(x+) 
0 
2,223,006 
2,505,744 
197,912 
10,605 
21,434,045 
23,348,679 
1,568,404 
128,946 
5 
2,425,066 
2,560,642 
15,566 
2,848 
19,211,039 
20,842,935 
1,370,492 
118,341 
10 
2,518,985 
2,452,339 
11,207 
5,153 
16,785,973 
18,282,293 
1,354,926 
115,492 
15 
2,453,156 
2,553,293 
25,473 
16,574 
14,266,988 
15,829,955 
1,343,719 
110,339 
20 
2,099,417 
2,362,519 
54,960 
14,803 
11,813,832 
13,276,662 
1,318,246 
93,766 
25 
1,899,275 
2,033,165 
102,802 
4,714 
9,714,415 
10,914,143 
1,263,286 
78,963 
30 
1,594,624 
1,875,483 
145,588 
13,331 
7,815,140 
8,880,977 
1,160,484 
74,249 
35 
1,441,657 
1,548,185 
145,900 
9,693 
6,220,516 
7,005,495 
1,014,896 
60,918 
40 
1,233,813 
1,306,900 
135,936 
7,464 
4,778,859 
5,457,310 
868,996 
51,225 
45 
967,744 
1,104,294 
121,010 
8,719 
3,545,046 
4,150,410 
733,060 
43,761 
50 
769,627 
888,042 
111,157 
9,413 
2,577,302 
3,046,116 
612,050 
35,042 
55 
552,402 
708,812 
96,854 
4,640 
1,807,675 
2,158,074 
500,893 
25,629 
60 
444,592 
491,871 
89,930 
5,081 
1,255,273 
1,449,261 
404,039 
20,989 
65 
304,835 
394,305 
82,843 
4,922 
810,681 
957,391 
314,108 
15,908 
70 
232,604 
241,976 
73,036 
4,334 
505,846 
563,086 
231,266 
10,986 
75 
136,466 
163,112 
63,871 
2,980 
273,242 
321,110 
158,229 
6,652 
80 
90,856 
87,698 
48,163 
1,662 
136,776 
157,998 
94,359 
3,672 
85 
45,920 
70,299 
46,196 
2,009 
45,920 
70,299 
46,196 
2,009 
Calculating personyears lived requires an estimate of the time between the two counts. This has been calculated using the YEARFRAC function in Excel on the basis of the date of the day following the time reference for the censuses. Counting days and dividing by 365 produces a slightly different estimate (5.3507 years) but has a negligible impact on the estimate of completeness.
The personyears of life lived is given in column 2 of Table 3 and is calculated from the numbers of the cumulated population in columns 2 and 3 of Table 2. For age 20, for example, as follows:
Table 3 Calculation of the cumulated populations, deaths and migrants, South African males, 20012007
Age 
PYL(x+) 
N(x) 
b(x+) 
r(x+)i(x+) 
d(x+) = X 
b(x+)r(x+) +i(x+) = Y 
a+bx 
Residuals y(a+bx) 
0 
119,775,275 


#N/A 
0.00000 

0.0047 

5 
107,136,837 
2,554,810 
0.02385 
0.01413 
0.01279 
0.00972 
0.0093 
0.0004 
10 
93,793,458 
2,611,355 
0.02784 
0.01472 
0.01445 
0.01312 
0.0111 
0.0020 
15 
80,461,835 
2,715,670 
0.03375 
0.01805 
0.01670 
0.01570 
0.0135 
0.0022 
20 
67,053,861 
2,577,889 
0.03845 
0.02042 
0.01966 
0.01803 
0.0168 
0.0013 
25 
55,129,886 
2,212,329 
0.04013 
0.02033 
0.02291 
0.01980 
0.0203 
0.0005 
30 
44,604,915 
2,020,991 
0.04531 
0.02223 
0.02602 
0.02308 
0.0237 
0.0006 
35 
35,344,071 
1,682,498 
0.04760 
0.02049 
0.02871 
0.02712 
0.0266 
0.0005 
40 
27,342,320 
1,469,826 
0.05376 
0.02294 
0.03178 
0.03082 
0.0300 
0.0008 
45 
20,537,160 
1,249,916 
0.06086 
0.02735 
0.03569 
0.03352 
0.0343 
0.0007 
50 
15,001,678 
992,684 
0.06617 
0.02891 
0.04080 
0.03726 
0.0398 
0.0026 
55 
10,574,924 
790,897 
0.07479 
0.03071 
0.04737 
0.04408 
0.0470 
0.0029 
60 
7,221,483 
558,171 
0.07729 
0.02396 
0.05595 
0.05334 
0.0564 
0.0030 
65 
4,716,866 
448,343 
0.09505 
0.02773 
0.06659 
0.06732 
0.0680 
0.0006 
70 
2,857,463 
290,826 
0.10178 
0.01619 
0.08093 
0.08559 
0.0836 
0.0020 
75 
1,585,932 
208,577 
0.13152 
0.02599 
0.09977 
0.10553 
0.1041 
0.0014 
80 
787,071 
117,144 
0.14884 
0.02230 
0.11989 
0.12654 
0.1261 
0.0005 
85 
304,201 







The numbers of people who turned x are shown in the third column of Table 3. For example, the number who turned 20 is estimated from the population numbers in columns 2 and 3 of Table 1 as follows:
The partial birth and death rates are shown in columns 4 and 6 of Table 3. The partial birth and death rates are calculated from the partial births (column 3 of Table 3) and the partial deaths (column 8 of Table 2) as follows for age 20, for example:
The partial growth rate less the partial net inmigration rate is shown in column 5 of Table 3 and is calculated for age 20, for example, using the cumulated populations given in columns 2 and 3 of Table 3 and cumulated net inmigration given in the last column of Table 2 as follows:
In order to plot the graph and fit the line to all of the data points, one starts by setting the lower age to 5 and the upper age to 84 (since the open interval for these data is 85+). The values of b(x+)  r(x+) + i(x+) plotted against d(x+) are shown in Figure 1.
Inspection of the diagnostic plots in Figure 1 suggests that the points lie fairly close to the fitted straight line, indicating that there is little migration which has not been accounted for. Thus there is little reason to alter the age range over which the line is fitted. Thus, as might be expected, increasing the minimum age has very little effect on the estimate of completeness of 91 per cent. Likewise, even though the results may be affected to some extent by a falling off of completeness at the older ages (see the application of the Synthetic Extinct Generations method [3] to these data), the estimate is little changed by excluding the last or the last two points (i.e. reducing the upper age of age interval used to fit the data). Dropping further points, however, increases completeness to implausible levels which suggests that the data (probably the population data) are far from perfect.
The coefficients of the straight line fitted to the points in Figure 1 are estimated as follows:
The relative completeness of enumeration of the census populations is estimated as follows:
Thus k_{2} > k_{1} and so we assume k_{2} = 1 and hence k_{1} = 0.9753 (i.e. the first population is undercounted relative to the second by some 2.5 per cent).
The completeness of reporting of deaths, c, is 91 per cent (relative to the 2007 count), calculated as follows:
The adjusted population as at the first census date is the enumerated population given in column 2 of Table 2 divided by k_{1}. For example the adjusted population for age 20 is
The adjusted population at the second census date is the enumerated population given in column 3 of Table 2 divided by k_{2}. Since, by assumption, k_{2} = 1, these numbers are the same as those given in column 3 of Table 2.
Next the deaths are adjusted for incompleteness by dividing the number of reported deaths in each age group shown in column 4 of Table 2 by the estimate of completeness. These numbers are shown in column 4 of Table 4. For example, for age 20 the number is derived from the number of reported deaths, 54 960, as follows:
The adjusted personyears of life lived (column 5 of Table 4) is the geometric average of the populations in columns 2 and 3 of Table 4 multiplied by the length (in years) of the period between the censuses, which in this case is 5.3541 years. For age 20 this is
The mortality rates adjusted for incompleteness of reporting of deaths (column 6 of Table 4) are derived by dividing the adjusted deaths by the adjusted personyears of life lived. For example, for the 2024 age group the adjusted rate is calculated as follows:
Table 4 Calculation of adjusted mortality rates, South African males, 20012007
Age 
Adjusted _{ 5}N_{x}(t_{1}) 
Adjusted _{ 5}N_{x}(t_{2}) 
Adjusted_{ 5}D_{x} 
Adjusted PYL(x,5) 
Adjusted _{5}m_{x} 
0 





5 
2,486,532 
2,560,642 
17,193 
13,510,001 
0.0013 
10 
2,582,831 
2,452,339 
12,378 
13,474,797 
0.0009 
15 
2,515,334 
2,553,293 
28,134 
13,568,508 
0.0021 
20 
2,152,629 
2,362,519 
60,701 
12,074,140 
0.0050 
25 
1,947,414 
2,033,165 
113,541 
10,653,675 
0.0107 
30 
1,635,041 
1,875,483 
160,796 
9,375,725 
0.0172 
35 
1,478,197 
1,548,185 
161,141 
8,099,564 
0.0199 
40 
1,265,085 
1,306,900 
150,136 
6,884,383 
0.0218 
45 
992,273 
1,104,294 
133,651 
5,604,563 
0.0238 
50 
789,134 
888,042 
122,768 
4,482,045 
0.0274 
55 
566,403 
708,812 
106,972 
3,392,442 
0.0315 
60 
455,861 
491,871 
99,325 
2,535,277 
0.0392 
65 
312,561 
394,305 
91,497 
1,879,609 
0.0487 
70 
238,500 
241,976 
80,666 
1,286,217 
0.0627 
75 
139,925 
163,112 
70,543 
808,863 
0.0872 
80 
93,159 
87,698 
53,194 
483,940 
0.1099 
85 
47,084 
70,299 
51,021 
308,032 
0.1656 
Estimates of probabilities of people aged x dying in the next 5 years, _{5}q_{x}, estimated from the adjusted rates of mortality which appear in column 6 of Table 4, are shown in the second column of Table 5. For example, the probability of a 20year old woman dying before reaching age 25 is calculated as follows:
The life table proportions of fiveyear olds alive at age x+5 estimated from the proportion alive at age x using these values appear in column 3 of Table 5. For example, the proportion alive at age 25 is calculated as follows:
Table 5 Calculation of smoothed mortality rates using a relational logit model life table, South African males, 20012007
Age 
_{5}q_{x} 
l_{x}/l_{5} 
Obs. Y(x) 
AIDS Cdn. ls(x) 
Cdn. Ys(x) 
Fitted Y(x) 
Fitted l(x) 
T(x) 
Smooth _{5}m_{x} 
0 









5 
0.0063 
1 

1.0000 


1 
50.898 
0.0032 
10 
0.0046 
0.9937 
2.5270 
0.9785 
1.9081 
2.0574 
0.9839 
45.739 
0.0030 
15 
0.0103 
0.9891 
2.2542 
0.9632 
1.6326 
1.7297 
0.9695 
40.856 
0.0025 
20 
0.0248 
0.9789 
1.9186 
0.9512 
1.4853 
1.5545 
0.9573 
36.039 
0.0043 
25 
0.0519 
0.9546 
1.5229 
0.9324 
1.3120 
1.3485 
0.9368 
31.303 
0.0090 
30 
0.0822 
0.9051 
1.1273 
0.8969 
1.0818 
1.0747 
0.8956 
26.722 
0.0159 
35 
0.0948 
0.8306 
0.7951 
0.8420 
0.8365 
0.7829 
0.8272 
22.415 
0.0206 
40 
0.1034 
0.7519 
0.5544 
0.7794 
0.6311 
0.5386 
0.7460 
18.482 
0.0241 
45 
0.1125 
0.6742 
0.3636 
0.7148 
0.4593 
0.3344 
0.6612 
14.964 
0.0244 
50 
0.1282 
0.5983 
0.1992 
0.6560 
0.3228 
0.1720 
0.5851 
11.848 
0.0234 
55 
0.1461 
0.5216 
0.0433 
0.6048 
0.2127 
0.0410 
0.5205 
9.084 
0.0258 
60 
0.1784 
0.4454 
0.1097 
0.5530 
0.1064 
0.0854 
0.4574 
6.640 
0.0337 
65 
0.2170 
0.3659 
0.2749 
0.4918 
0.0163 
0.2313 
0.3864 
4.530 
0.0503 
70 
0.2711 
0.2865 
0.4562 
0.4119 
0.1781 
0.4237 
0.3000 
2.814 
0.0717 
75 
0.3580 
0.2089 
0.6659 
0.3178 
0.3819 
0.6661 
0.2088 
1.542 
0.1008 
80 
0.4311 
0.1341 
0.9327 
0.2173 
0.6408 
0.9740 
0.1248 
0.708 
0.1470 
85 
#N/A 
0.0763 
1.2470 
0.1201 
0.9959 
1.3964 
0.0577 
0.252 
0.2081 
The logit transformations of the proportions surviving appear in column 4 of Table 5. For example, the logit transformation of the l_{20} is calculated as follows:
The logit transformation of the conditional life table for males based on the AIDS life table with e_{0}=50 in column 5 of Table 5 appears in column 6 of Table 5. As can be seen from Figure 2, the AIDS model does not fit the data particularly well, but fits better than any table which does not reflect the impact of HIV on mortality.
The coefficients, α and β are determined as the intercept and slope of the straight line fitted to the logit transformations in columns 4 and 6 of Table 5 over the range of ages chosen by the user (45 and 80 in this example), namely 0.2119 and 1.1893 respectively.
These coefficients are then applied to the logit transformation of the conditional model life table to produce the fitted logits in column 7 of Table 5. Thus, for example, the fitted logit at age 20 is calculated as follows:
These values are then used to produce the fitted life table in column 8 of Table 5. For example, the value at age 20 is calculated as follows:
The conditional years of life lived, T_{x}, which appear in column 9 of Table 5 are then calculated from the fitted life table and these numbers are then used to produce the smoothed mortality rates which appear in column 10 of Table 5. For example, for age 80
The estimate of completeness is 91 per cent. The first check on this result is a comparison with the results for the opposite sex. For example, applying the same method as described above for men to the data for women during the same period (GGB_South Africa_females [7]) gives an estimate of completeness of 89 per cent. Past research (Dorrington, Moultrie and Timæus 2004) leads to the expectation that the estimates should be similar, so the results are sufficiently close to validate the estimates.
A second check on the results is to compare them with the result from the Synthetic Extinct Generations method [3](SEG_South Africa_males [8]), which estimated the completeness of death reporting over the age range 5 to 84 to be 94 per cent, which is also sufficiently close to validate the results.
A third check is to compare estimates of various key indicators of mortality with those from other sources, such as previous estimates for the country or the World Population Prospects (UN Population Division 2011). The estimate of _{45}q_{15} from the observed mortality rates after adjusting for incompleteness is 52.3 per cent, while the estimate of _{45}q_{15} from the WPP for the period 20002005 is 52.8 per cent, again suggesting little reason to question the results.
As a matter of interest, application of the Brass Growth Balance method [1] to these data (estimating the population in the middle of the period as the average of the two survey populations) provides an estimate of completeness, using the same age range, of 85 per cent. Increasing the minimum age of range of the data used to fit the straight line to 35 increases the estimate to 88 per cent, still somewhat lower than the estimate of 91 per cent produced above.
As mentioned already, when deciding on the age range over which to fit the straight line, each of the open intervals from 85+ down to 75+ produced virtually the same estimate of the completeness of death reporting. However, below 75+ the estimates increase to 100 per cent for 70+, 105 per cent for 65+ and 108 per cent for 60+. Even though it is probable that the census and survey underestimate the number of men, the undercount is likely to have been concentrated among young adults and is unlikely to have been so great as to raise the completeness of reporting of the deaths relative to the estimate of the population to more than 100 per cent. Moreover, other things being equal, the lower the age of the open interval the less robust the estimate of completeness. Thus, the lower estimates obtained from openended age groups for higher ages are preferred.
Generally there are two sorts of problems with the deaths data: those that lead to under/over coverage that is constant by age, which is precisely what the method is intended to address, and those which lead to differential coverage by age, which can distort the estimates. Although the general approach remains essentially the same irrespective of the source of the death data, different sources of death data are prone to different biases which might impact on the interpretation of the results. These are illustrated by way of particular examples, but, in general terms, the analyst needs to look out for the following biases in the death data.
(i) Vital registration
If the proportionate split of the population between urban and rural (or appropriate proxies) areas differs significantly by age and the completeness of reporting of deaths in urban areas is significantly higher than it is in rural areas, then the assumption that completeness is independent of age is likely to be violated by a falling off of completeness with age at ages over 50 if a proportion of people move from urban to rural areas on retirement. If ignored, this violation is likely to lead to an underestimate of the average level of completeness.
(ii) Deaths reported by households
The data are subject to four potential problems:
(iii) Deaths recorded in health facilities
Little is known about how well this source of data works. However, it can be expected that completeness would depend on the distribution of health services from which the data have been gathered, and in many developing countries such services are likely to be concentrated in urban areas. So, again, if the proportion of the population living in urban rather than rural areas varies with age, then completeness cannot be assumed to be independent of age. It is also possible that certain causes will predominate in facilities and if these causes are significant, and agerelated, this could lead to a further violation of the assumption of constant completeness by age.
The examples below use the same data as used in the GGB_South Africa_males [4] and GGB_South Africa_females [7] workbooks with the exception that instead of using the vital registration as the source of the death data, deaths are estimated from deaths reported by households in the 2001 census and the 2007 Community survey as having occurred in the year preceding the census/survey. These numbers are given in Table 6.
Table 6 Deaths reported by households to have occurred in the year preceding census/survey, South Africa

2001 Census 
2007 Community Survey 

Age 
Males 
Females 
Males 
Females 
04 
35,873 
32,096 
48,322 
44,418 
59 
3,868 
3,155 
4,505 
5,216 
1014 
2,590 
2,284 
3,442 
3,259 
1519 
5,628 
5,122 
8,246 
7,878 
2024 
10,976 
13,246 
16,360 
21,702 
2529 
17,787 
19,727 
27,551 
35,840 
3034 
20,038 
18,292 
34,832 
42,576 
3539 
19,816 
15,521 
38,061 
34,809 
4044 
17,417 
12,124 
33,604 
28,823 
4549 
15,840 
10,105 
27,829 
20,973 
5054 
15,077 
9,144 
28,223 
18,891 
5559 
12,781 
7,755 
22,868 
13,118 
6064 
13,428 
10,367 
18,775 
14,912 
6569 
11,820 
10,195 
17,532 
14,298 
7074 
11,885 
10,809 
14,879 
14,645 
7579 
8,794 
8,393 
12,966 
14,151 
8084 
7,484 
9,371 
9,204 
12,063 
85+ 
7,115 
12,389 
11,735 
18,178 
The numbers of deaths occurring between the date of the census (midnight between 9 and 10 October 2001) and the survey (assumed to be midnight between 14 and 15 February 2007) are estimated using the Estimating deaths_South Africa_males_hhd [9] and the Estimating deaths_South Africa_females_hhd [10] spreadsheets.
Applying the Generalized Growth Balance method to these data for males (in the GGB_South Africa_males_hhd [11] workbook), suggests that these estimates of the number of deaths are more or less as completely reported as the vital registration. However, they estimate _{45}q_{15} at 54.8 per cent which is slightly higher than that produced using registered deaths. Applying the Generalized Growth Balance method to these data for females (in the GGB_South Africa_females_hhd [12] workbook), suggests that the deaths of women reported by households are far less complete than the registered deaths. It also estimates _{45}q_{15} at 50.9 per cent, which is much higher (and less plausible relative to the probability for males) than the 42 per cent produced using registered deaths.
The reason for the much poorer performance of the method when applied to deaths of women reported by households can be seen by a comparison of the estimated numbers of deaths for the period derived from deaths reported by households to the numbers expected after correcting the vital registration for incompleteness of reporting, as shown in Table 7. From this we see that there is a significant decline in completeness of reporting of deaths of women by households with age from age 55, probably as the result of disintegration of households on the death of these women, usually because these households were headed by the women who died.
There is also evidence of overreporting of deaths below age 30 for males and 25 for females, possibly because their deaths are reported by more than one household.
Table 7 Ratio of estimates of deaths derived from deaths for 20012007 reported by households to the expected numbers of deaths (corrected for incompleteness), South Africa

Males 

Females 


Age 
Reported 
Expected 
Ratio 
Reported 
Expected 
Ratio 
04 






59 
22,683 
17,193 
132% 
22,995 
14,670 
157% 
1014 
16,462 
12,378 
133% 
15,173 
10,417 
146% 
1519 
38,013 
28,134 
135% 
35,666 
27,050 
132% 
2024 
74,934 
60,701 
123% 
95,993 
85,167 
113% 
2529 
124,403 
113,541 
110% 
152,718 
155,452 
98% 
3034 
150,792 
160,796 
94% 
166,488 
171,801 
97% 
3539 
159,016 
161,141 
99% 
137,837 
142,328 
97% 
4044 
140,172 
150,136 
93% 
111,910 
116,506 
96% 
4549 
120,016 
133,651 
90% 
85,284 
94,022 
91% 
5054 
118,989 
122,768 
97% 
76,941 
82,330 
93% 
5559 
97,977 
106,972 
92% 
57,353 
72,605 
79% 
6064 
88,088 
99,325 
89% 
69,220 
79,395 
87% 
6569 
80,451 
91,497 
88% 
67,007 
86,665 
77% 
7074 
72,827 
80,666 
90% 
69,536 
94,017 
74% 
7579 
59,632 
70,543 
85% 
61,942 
88,894 
70% 
8084 
45,365 
53,194 
85% 
58,410 
77,590 
75% 
85+ 
51,779 
51,021 
101% 
83,753 
108,712 
77% 
To simulate the situation where only the most recent census asked about deaths in the previous year, the number of deaths in each age group between the times of the 2001 census and the 2007 Community Survey using only the deaths reported by households in the 2007 Community Survey are estimated as follows:
Applying the method to these estimates of the deaths produces estimates of _{45}q_{15} of 58.6 per cent for males and 57.8 per cent for females. Unlike the previous estimates, these are estimates of mortality in the year preceding the second census/survey. They might therefore be expected to be higher than those for the whole period, since mortality has been increasing over the period due to HIV/AIDS. However, as might also be expected, deriving an estimate from a single year of deaths (derived, in addition, in this case from a relatively small sample survey) produces far less reliable estimates, particularly in the case (for these data) of females. Alternative estimates (Bradshaw, Dorrington and Laubscher 2012) suggest that for 2006 the correct probabilities should be closer to 55 per cent for males and 45 per cent for females.
The General Growth Balance method follows the same logic as Brass’s Growth Balance method (Brass 1975), which had its origins in work by Carrier (1958), who first proposed a way of estimating mortality from the age distribution of deaths. The method derives from the simple relationship found in the balancing equation for a population (assumed for convenience of explanation to be) closed to migration. In such a population, the number of people in the population at time t_{2} = the number at time t_{1} plus the births that have occurred between time t_{1} and t_{2} less the deaths that have occurred between times t_{1} and t_{2}, i.e.
, where B and D are the births and deaths, respectively, that occurred between times t_{1} and t_{2}. This equation can be generalized to hold for any population aged x and older, provided we have an estimate of the number of people who turned x (i.e. joined the age interval through aging) between the times t_{1} and t_{2},
, and the number of deaths aged x and older that occurred between times t_{1} and t_{2},
. Thus
If we rewrite equation (1) as
and divide through by the personyears of exposure between times t_{1} and t_{2} ,
, one can express this balance equation in terms of rates, i.e.
where
and
b(x+) and d(x+) are often referred to as partial or segmental birth and death rates, respectively.
These relationships only hold if there is complete and accurate recording of birthdays and deaths by age between times t_{1} and t_{2}, and counting of the population by age at times t_{1} and t_{2}.
Now, suppose that instead of accurate data only a proportion (the same for all ages) of deaths are reported, and only a (different) proportion (the same for all ages) of each census population, are counted. Suppose further that, instead of the true values
,
and
, we have reported values
,
and
such that
,
and
.
Then, if we use the following approximations:
and
then
where
and
where
and Equation 2 becomes
i.e.
where
and
From this one can solve for k_{1}, k_{2} and hence c, on the assumption that coverage of the better enumerated census is 100 per cent, by assuming the larger of k_{1} and k_{2} = 1.
There are two aspects to determining the straight line that best represents the relationship between the partial birth and death rates, namely, the choice of method and the choice of points used to determine the slope and intercept.
Fitting the straight line using unweighted least squares regression is not recommended since this method gives too much weight to outliers, which tend to be less reliable, particularly at the older ages. Thus it is recommended that one fit the line using a more robust method such as the ‘mean’ line (i.e. the line defined as that joining the two points represented by the mean of the vertical axis values and the mean of the horizontal axis values of the first half and the second half of the age range) or the ‘trimmed mean’ line (i.e. the same as the mean line except that the average of the points is a weighted average  weighting the less reliable points, usually at the extremes, less than the other points). These methods are explained in detail in Manual X (UN Population Division 1983: 144145). An alternative is described in more detail in the UN Manual on Adult Mortality (UN Population Division 2002: 105110). It is similar to the ‘mean’ line, except that one splits the range of points into three equally sized groups, and determines the line that joins the medians of the independent and dependent variables in the lowest third and the highest third of points.
Bhat (2002) points out that each method has its drawbacks and suggests, since it matters not whether the partial birth or partial death rates are treated as dependent variable, that orthogonal regression is the best method for dealing with age misstatement. This reflects both vertical and horizontal distance from the line (by minimising the orthogonal residual sum of squares (ORSS) =
). Using this method, the c, the
completeness of the death reporting, is estimated as the ratio of the standard
deviation of the partial death rates to the standard deviation of the partial
birth rates. The intercept is the mean of the partial birth rates, minus the
mean of the partial death rates divided by c. This is the
approach used in the applications of the Generalized Growth Balance method in
the accompanying workbook.
This method is less vulnerable to age misreporting than the Synthetic Extinct Generations method [3]. However, the common tendency to exaggerate the age reported at death (relative to that recorded at census) will manifest itself by the plotted points falling off to the right (i.e. below the fitted line) over the range of exaggerated ages. This can be catered for by reducing the age of the open interval to the point which removes this effect.
Migration which is not allowed for in the model is likely to affect the young adult population (mainly between 20 and 35) but to have much less effect on deaths, which largely occur in old age. Unaccountedfor immigration will tend to lower the slope and hence lead to an overestimate of the extent of death registration and an underestimate of mortality rates. Unaccountedfor emigration will have the opposite effect.
Often one lacks reliable estimates of the net number of migrants by age over the intercensal period. In such situations one could proceed as follows. If the migration is significant and unknown and the points above age 30 lie close to a straight line, one might estimate completeness by fitting the straight line to the data from age 35 and above. If migration is slight, some demographers advocate fitting the straight line to data down to age 5 to limit this distortion, on the assumption that any differences in completeness of reporting of deaths at these younger ages from that of the older ages is unlikely to lead to any major distortions since the mortality is very light between ages 5 and 14. Others (Hill, You and Choi 2009) suggest that provided the migration is not too significant, an improved estimate might be provided by averaging the estimate of completeness produced with that produced by applying the Synthetic Extinct Generations method [3] to the same data. Although using these adaptations probably produces better estimates than simply ignoring migration, there is, unfortunately, little research into the accuracy of the estimated completeness produced by these adaptations.
Fluctuations in the completeness of death registration with age are likely to introduce curvature in the pattern of points. Consequently, one of the strengths of this method is that if the points for successive age boundaries fall on a reasonably straight line, then it is probably reasonable to assume that completeness is constant with respect to age. However, where some but not all the points lie on a straight line, one way of deciding which points to discard is to calculate the segmental growth rate for each successive open interval and then use those points for which the values of
are reasonably consistent.
Perhaps the most important limitation of the method is that the plot of partial birth rates against partial death rates is, with the exceptions mentioned above, diagnostically quite limited.
If the ages were recorded accurately and the assumption of constant census coverage by age held, then the method could be adapted to deal with the situation where completeness of reporting of the deaths was constant only for a limited age range (x to x+n) by limiting the age range of the balance equation. Thus equation 2 would become
,
where
and
.
The LHS of the analogous regression equation based on observations becomes
.
Perhaps because data in developing countries are rarely accurate enough, little experience exists with how well this alternative approach works in practice.
Analysis of the sensitivity of the method to common data errors and violation of the assumptions is fairly limited. However, the reader is referred to Hill, You and Choi (2009) for an analysis of the assumptions underlying the death distribution methods in the absence of HIV and to Dorrington and Timæus (2008) for an analysis in a population experiencing significant HIV. Murray, Rajaratnam, Marcus et al. (2010), in contrast, used stochastic simulations to assess these methods, concluding that the methods were not particularly reliable. However, to date their work has had very limited impact on the use of these methods, possibly because their description of their simulations is short on detail and because their assessment is based on perhaps unrealistically high migration.
Bhat M. 2002. "General Growth Balance method: A reformulation for populations open to migration", Population Studies 56(1):2334. doi: http://dx.doi.org/10.1080/00324720213798 [13]
Blacker J. 1988. An Evaluation of the Pakistan Demographic Survey. Karachi: Pakistan Federal Bureau of Statistics.
Bradshaw D, RE Dorrington and R Laubscher. 2012. Rapid Mortality Surveillance Report 2012. Cape Town: South African Medical Research Council. http://www.mrc.ac.za/bod/RapidMortality2011.pdf [14]
Brass W. 1975. Methods for Estimating Fertility and Mortality from Limited and Defective Data. Chapel Hill NC: Carolina Population Centre.
Carrier NH. 1958. "A note on the estimation of mortality and other population characteristics, given death by age", Population Studies 12(2):149163. doi: http://dx.doi.org/10.2307/2172187 [15]
Dorrington RE, TA Moultrie and IM Timæus. 2004. Estimation of mortality using the South African 2001 census data. Monograph 11. Centre for Actuarial Research, University of Cape Town. http://www.commerce.uct.ac.za/care/Monographs/Monographs/Mono11.pdf [16]
Dorrington RE and IM Timæus. 2008. "Death Distribution Methods for Estimating Adult Mortality: Sensitivity Analysis with Simulated Data Errors, Revisited," Paper presented at Population Association of America 2008 Annual Meeting. New Orleans, Louisiana, 1719 April.
Hill K. 1987. "Estimating census and death registration completeness", Asian and Pacific Census Forum 1(3):813, 2324. http://hdl.handle.net/10125/3602 [17].
Hill K, D You and Y Choi. 2009. "Death distribution methods for estimating adult mortality: Sensitivity analysis with simulated data error", Demographic Research 21(Article 9):235254. doi: http://dx.doi.org/10.4054/DemRes.2009.21.9 [18]
Murray CJL, JK Rajaratnam, J Marcus, T Laakso and AD Lopez. 2010. "What can we conclude from death registration? Improved methods for evaluating completeness", PLoS Med 7(4):e1000262. doi: http://dx.doi.org/10.1371/journal.pmed.1000262 [19]
Timæus IM. 2004. "Impact of HIV on mortality in Southern Africa: Evidence from demographic surveillance," Paper presented at Seminar of the IUSSP Committee "Emerging Health Threats" HIV, Resurgent Infections and Population Change in Africa. Ougadougou, 1214 February.
UN Population Division. 1983. Manual X: Indirect Techniques for Demographic Estimation. New York: United Nations, Department of Economic and Social Affairs, ST/ESA/SER.A/81. http://www.un.org/esa/population/techcoop/DemEst/manual10/manual10.html [20]
UN Population Division. 2002. Methods for Estimating Adult Mortality. New York: United Nations, Department of Economic and Social Affairs, ESA/P/WP.175. http://www.un.org/esa/population/techcoop/DemEst/methods_adultmort/methods_adultmort.html [21]
UN Population Division. 2011. World Population Prospects: The 2010 Revision, Volume I: Comprehensive Tables. New York: United Nations, Department of Economic and Social Affairs, ST/ESA/SER.A/313. http://esa.un.org/unpd/wpp/Documentation/pdf/WPP2010_VolumeI_ComprehensiveTables.pdf [22]
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[13] http://dx.doi.org/10.1080/00324720213798
[14] http://www.mrc.ac.za/bod/RapidMortality2011.pdf
[15] http://dx.doi.org/10.2307/2172187
[16] http://www.commerce.uct.ac.za/care/Monographs/Monographs/Mono11.pdf
[17] http://hdl.handle.net/10125/3602
[18] http://dx.doi.org/10.4054/DemRes.2009.21.9
[19] http://dx.doi.org/10.1371/journal.pmed.1000262
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