Bennett and Horiuchi (1981, 1984) generalized the Preston and Coale method for estimating the completeness of the reporting of deaths relative to an estimate of the population, into what has eventually become known as the Synthetic Extinct Generations (SEG) method. Basically these methods make use of the observation that, in a closed population, the number of people of a given age, a, alive at a point in time must equal the number of people who will die from that age forward. The key insight on which SEG methods are based is that the future stream of deaths of a cohort can be replaced by current deaths at each age above a if the effects of future agespecific population growth can be taken into account. The simplest example is a stationary (life table) population, in which future deaths above age a will be equal to current deaths above that age. Somewhat more complex is the case where the population is stable (i.e. a population with an unchanging adult age distribution growing at a constant rate, r, each year) and closed to migration. In this case, if the reported data are accurate, the number of deaths at age x, t years in the future, will equal the number of deaths at age x currently, multiplied by
. This is the model underlying the Preston and Coale method [1].
In the more general case where the population is not stable, an equivalent relationship exists if one replaces
by
where r(y¸t) represent the growth rate of the population aged y at time t.
If the deaths reported at time t can be assumed to be reported to the same extent, c, at every adult age, then the estimate of the future number of cohort deaths will be underestimated to the same extent. Thus, it is possible to estimate the completeness of reporting of deaths by dividing the sum of the estimates of future cohort deaths derived from the number of deaths at any date by the population at the same date. Mortality rates can then be estimated by dividing the numbers of deaths reported in each adult age group by c and then dividing these numbers by an estimate of the population exposed to risk based on the population used to estimate the partial birth and death rates.
Before applying this method, you should examine 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 [2] spreadsheet).
The SEG methodology uses agespecific population growth rates in its calculations. If the completeness of census enumeration varies from one census to the next by a proportionately constant amount at all ages, such growth rates will be biased by a fixed amount, delta. The Generalized Growth Balance [3] methodology explicitly estimates this bias. The SEG methodology does not explicitly estimate delta, but nonzero values of delta result in a linear trend in estimates of completeness of death recording with age. Thus delta can be estimated iteratively by finding the value that produces coverage estimates that are constant by age between selected lower and upper age limits.
In applying this method, analysts must take particular care with the following.
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 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 make use of the Estimating death [2]s 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.
Agespecific growth rates adjusting for migration and differential census coverage are estimated from the two census populations and the numbers of migrants over the intercensal period by age group as follows:
where
is the population aged between x and x + 5 at time t, _{5}NM_{x} is the net number of migrants (in less outmigrants) aged between x and x + 5, and t_{1} and t_{2} are the times of the two censuses. Delta is the correction for the completeness of one census relative to the other. It is either set equal to the estimate from the Generalized Growth Balance method [3], or solved for iteratively as explained below.
This can be done in one of several ways.
The number of people who turned x during the period over which the deaths were reported is estimated from the reported deaths as follows:
and
where A is the age at the start of the open interval, _{n}r_{x} is the annual population growth rate in the age group x to x+n last birthday, and e_{A} is the life expectancy at age A.
The number of people aged x to x + 4 last birthday during the period over which the deaths were reported is estimated from the numbers who turned x in fiveyear steps as follows:
The number of people aged x to x + 4 during the period over which the deaths are reported is estimated from the census populations by multiplying the geometric mean of the numbers in that age group in the two census populations by the length of the period between the two censuses (measured in years) as follows:
$$\text{}$$Step 6: Calculate the ratios of the estimates derived from deaths to those derived from the census populations
Two sets of ratios of the estimates derived from the deaths to those derived from the census population are calculated. The first is the ratios in quinquennial age groups, which are calculated directly. The second is the ratios of the numbers from age x to that age of the open interval, A, with the numbers of people who turned x to A1 during the period being calculated as the aggregate of the numbers in fiveyear age groups between ages x and A5. In other words,
Step 7: Estimate the completeness of reporting of deaths
In order to determine the level of completeness of reporting one first needs to decide if the growth rates need to be corrected for relative completeness of the population censuses. The interpretation of the plots of the ratios is discussed in more detail below. However, essentially the amount by which the growth rates need to be corrected (delta) for relative completeness of the census populations is identified as the amount which produces the most level set of ratios by age. The Method spreadsheet is set up so that Solver (Data, Solver, Solve) will find the value of delta that minimizes the absolute deviation from the mean of the ratios over the age range specified by the user.
It is suggested that the intercept, a, from the application of the Generalized Growth Balance method [3] to the same data be used as an initial estimate of delta. If this estimate of delta produces a level series of ratios across adult ages but with significant curvature downward at the older ages, this could indicate a fall off of completeness at the older ages. This might be the case if, for example, people retired from urban areas to rural areas, where completeness of registration was lower, or there was a drop off in reporting of deaths by households due to disintegration of some households on the death of a member. In such a situation it is important not to set delta to produce a level set of ratios, but rather to use the initial value.
If one is solving for both delta and the life expectancies iteratively, the values of life expectancies will need to be pasted from the Life expectancies spreadsheet into the Method spreadsheet and a new estimate of delta set. This process may need to be repeated two or three times, until there is no change in the life expectancies.
Finally, one decides on the age range of ratios to be used to determine the completeness. If there is a significant curvature upward at the older ages, this probably indicates age exaggeration, particularly for deaths, and one needs to try and identify an age for the open interval below which the age exaggeration is not significant. If completeness drops off at ages below 35, this could indicate unaccounted for outmigration. If this is suspected then one should exclude these ages from determining delta or completeness.
Completeness is estimated from the quinquennial age groupspecific ratios. In order to produce a robust estimate it is calculated as the sum of 50 per cent of the median plus 25 per cent of each of the 75^{th} and 25^{th} percentile of these ratios.
In order to compute mortality rates one needs first to correct the census population for relative under enumeration. This is achieved by multiplying the numbers from the first census by
, and the numbers from the second census by 1, if delta is less than zero, and the reverse if delta >0.
The adjusted personyears of exposure, PYL^{a}(x,5), are estimated by multiplying the geometric average of the corrected populations by the length of the period between the censuses (in years) 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:
If it is decided that completeness fell after retirement then the estimates of the rates at these ages might be improved by replacing c by the age groupspecific estimates of completeness at these ages. There is an option in the spreadsheet to implement this.
Note that technically one could drop the adjustment for undercoverage of one census relative to the other 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 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 spreadsheet. 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.
The life expectancies, which are of particular interest if one wants to estimate the life expectancies at the older ages iteratively, are derived as follows:
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 SEG 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 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:
Agespecific growth rates less the net inmigration rate and adjusted for differential census coverage appear in column 6 of Table 2. They are calculated for the 20 to 25 age group, for example, using the populations given in columns 2 and 3, the net inmigration given in column 5 of Table 2 and delta (estimated below) as follows:
where 5.3541 is the time between the census and survey calculated using the YEARFRAC functions in Excel.
Table 2 Growth rates and estimate of the numbers who turned x and the numbers aged between x and x+5 derived from the numbers of deaths, South African males, 20012007
Age 
_{5}N_{x}(t_{1}) 
_{5}N_{x}(t_{2}) 
_{5}D_{x} 
_{5}NM_{x} 
_{5}r_{x} 
Est N_{x} 
Est _{5}N_{x} 


0 
2,223,006 
2,505,744 
197,912 
10,605 
0.0168 



5 
2,425,066 
2,560,642 
15,566 
2,848 
0.0053 
2,304,653 
11,334,968 

10 
2,518,985 
2,452,339 
11,207 
5,153 
0.0101 
2,229,335 
11,405,753 

15 
2,453,156 
2,553,293 
25,473 
16,574 
0.0016 
2,332,967 
11,556,063 

20 
2,099,417 
2,362,519 
54,960 
14,803 
0.0161 
2,289,459 
10,871,687 

25 
1,899,275 
2,033,165 
102,802 
4,714 
0.0076 
2,059,216 
9,851,950 

30 
1,594,624 
1,875,483 
145,588 
13,331 
0.0242 
1,881,564 
8,529,425 

35 
1,441,657 
1,548,185 
145,900 
9,693 
0.0074 
1,530,206 
7,153,512 

40 
1,233,813 
1,306,900 
135,936 
7,464 
0.0050 
1,331,199 
6,238,580 

45 
967,744 
1,104,294 
121,010 
8,719 
0.0184 
1,164,233 
5,276,384 

50 
769,627 
888,042 
111,157 
9,413 
0.0199 
946,320 
4,242,847 

55 
552,402 
708,812 
96,854 
4,640 
0.0405 
750,818 
3,191,145 

60 
444,592 
491,871 
89,930 
5,081 
0.0122 
525,640 
2,332,526 

65 
304,835 
394,305 
82,843 
4,922 
0.0407 
407,371 
1,662,114 

70 
232,604 
241,976 
73,036 
4,334 
0.0007 
257,475 
1,106,744 

75 
136,466 
163,112 
63,871 
2,980 
0.0249 
185,223 
721,856 

80 
90,856 
87,698 
48,163 
1,662 
0.0148 
103,519 
412,486 

85 
45,920 
70,299 
46,196 
2,009 
0.0683 
61,475 

The estimates derived after applying the Generalized Growth Balance method [3] to the same data are as shown in column 2 of Table 3.
The ratio of the reported deaths in the age group 10 to 39 last birthday to those in the age group 40 to 59 last birthday from column 4 of Table 2 is
The life expectancies of the male Princeton West model life table which corresponds to this are determined (from the table in the Life expectancies spreadsheet of the workbook) by interpolation and are shown in column 3 of Table 3. For example for age 65:
Solving for the life expectancy and delta iteratively by starting with the estimates from the West table produces an estimate of delta (as explained in more detail below) of ‑0.0066 and the final estimates of life expectancy which appear in column 4 of Table 3.
Table 3 Life expectancies from different sources, South African males 20012007
x 
Generalized Growth Balance 
Princeton West 
Iterative estimates 
Delta fixed to GGB estimate 
65 
11.7 
9.45 
11.6 
11.7 
70 
9.4 
7.37 
9.3 
9.4 
75 
7.4 
5.55 
7.3 
7.4 
80 
5.7 
4.06 
5.6 
5.7 
85 
4.4 
2.90 
4.3 
4.4 
Since the prevalence of HIV/AIDS was high in South Africa one cannot use the estimates derived from the West life tables given in the Life expectancies spreadsheet of the workbook in estimating the completeness of reporting of deaths. In addition, since – discussed below – it appears that completeness could be falling with age for ages above age 55, the iterative estimates may not be ideal. Thus for this example, delta is set equal to the intercept, a, from the application of the Generalized Growth Balance method [3] to the same data, and the life expectancies are as appear in column 5 of Table 3.
The number of people who turned x during the period between the two censuses as estimated from the numbers of deaths using an open interval of 85+, growth rates from column 6 of Table 2 and the estimate of life expectancy at age 85 of 4.347 given in the fifth column of Table 3, is as shown in column 7 of Table 2. For example, the estimate of the number of people who turned 80 in the period between the censuses is calculated as follows, using the growth rate for the population in open interval 85+ of 0.0638 and the growth rate for the population aged between 80 and 85 of 0.0148, is:
The number of people aged x to x+4 last birthdays during the period between the two censuses, estimated from the reported deaths is given in column 8 of Table 2. For example, the number who turned 20 to 24 last birthday is calculated as follows:
The number of people aged between x and x + 5 during the period between the two censuses appears in column 2 of Table 4 and is calculated for the 20 to 24 age group, for example, using the populations given in columns 2 and 3 of Table 2 and the time between the two censuses, as follows:
Table 4 The number aged x to x+4 last birthday estimated from the census population and the ratios of the estimates derived from the numbers of deaths to this, South African males, 20012007
Age 
Obs _{5}N_{x} 
c: _{5}N_{x} 
c: _{A}_{x}N_{x} 
0 
12,636,377 


5 
13,341,976 
0.8496 
0.8981 
10 
13,307,209 
0.8571 
0.9050 
15 
13,399,755 
0.8624 
0.9130 
20 
11,923,972 
0.9118 
0.9231 
25 
10,521,174 
0.9364 
0.9256 
30 
9,259,118 
0.9212 
0.9230 
35 
7,998,828 
0.8943 
0.9235 
40 
6,798,761 
0.9176 
0.9322 
45 
5,534,858 
0.9533 
0.9371 
50 
4,426,301 
0.9586 
0.9310 
55 
3,350,250 
0.9525 
0.9191 
60 
2,503,746 
0.9316 
0.9028 
65 
1,856,232 
0.8954 
0.8865 
70 
1,270,220 
0.8713 
0.8799 
75 
798,803 
0.9037 
0.8885 
80 
477,921 
0.8631 
0.8631 
The ratios of the numbers of people aged between x and x + 5 during the period between the censuses estimated from the reported deaths (column 8 of Table 2) to those estimated from the censuses (column 2 of Table 4) are given in columns 3 and 4 of Table 4. Examples of these calculations for age 65 are as follows:
Setting delta to the intercept of the application of the Generalized Growth Balance method [3] produces a series of ratios which, although reasonably level, appears to fall off with increasing age from about age 50 (see from Figure 1). Thus for this example Solver was not used to estimate delta.
Completeness was estimated from the ratios in the age range 25 to 64. This was done to avoid, to some extent, biasing the estimate downwards due to the falling off of the ratios at the extreme ages although the method of determining the estimate is fairly robust to fluctuations at individual ages. This produced an estimate of completeness of 94 per cent as follows:
where 0.9340 is the median, 0.9203 the 25^{th} percentile and 0.9527 the 75^{th} percentile of the ratios in column 3 of Table 4 between ages 25 and 65.
The adjusted population as at the first census date which appears in column 2 of Table 5 is the enumerated population given in column 2 of Table 2 multiplied by exp(‑(‑0.00467)x5.3541) since delta is less than 0. For example the adjusted population for age 20 is
The adjusted population at the second census date which appears in column 3 of Table 5 is the enumerated population given in column 3 of Table 2 since delta is less than 0.
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 5. For example, for age 20 the number is derived from the number of reported deaths, 54 960, as follows:
As it appears that completeness may have declined at the older ages, the option to use agespecific completeness above age 65 is chosen. Thus, for example, the number of deaths between 70 and 75 corrected for incompleteness is calculated as follows:
The adjusted personyears of life lived (column 5 of Table 5) is the geometric average of the populations in columns 2 and 3 of Table 5 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 5) 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:
[[wysiwyg_mathjax::]]
Table 5 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 
16,644 
13,510,001 
0.0012 
10 
2,582,831 
2,452,339 
11,983 
13,474,797 
0.0009 
15 
2,515,334 
2,553,293 
27,236 
13,568,508 
0.0020 
20 
2,152,629 
2,362,519 
58,764 
12,074,140 
0.0049 
25 
1,947,414 
2,033,165 
109,919 
10,653,675 
0.0103 
30 
1,635,041 
1,875,483 
155,667 
9,375,725 
0.0166 
35 
1,478,197 
1,548,185 
156,001 
8,099,564 
0.0193 
40 
1,265,085 
1,306,900 
145,347 
6,884,383 
0.0211 
45 
992,273 
1,104,294 
129,387 
5,604,563 
0.0231 
50 
789,134 
888,042 
118,852 
4,482,045 
0.0265 
55 
566,403 
708,812 
103,560 
3,392,442 
0.0305 
60 
455,861 
491,871 
96,156 
2,535,277 
0.0379 
65 
312,561 
394,305 
92,518 
1,879,609 
0.0492 
70 
238,500 
241,976 
83,824 
1,286,217 
0.0652 
75 
139,925 
163,112 
70,679 
808,863 
0.0874 
80 
93,159 
87,698 
55,803 
483,940 
0.1153 
85 
47,084 
70,299 
53,524 
308,032 
0.1738 
Step 9: Smooth using relational logit model life table
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 5, are shown in the second column of Table 6. 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 6. For example the proportion alive at age 25 is calculated as follows:
[[wysiwyg_mathjax::]]
Table 6 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) 
e(x) 
Smooth _{5}m_{x} 
0 










5 
0.0061 
1 

1.0000 


1 
51.206 
51.2 
0.0030 
10 
0.0044 
0.9939 
2.5433 
0.9785 
1.9081 
2.0984 
0.9852 
46.243 
46.9 
0.0028 
15 
0.0100 
0.9894 
2.2705 
0.9632 
1.6326 
1.7676 
0.9717 
41.351 
42.6 
0.0024 
20 
0.0240 
0.9796 
1.9350 
0.9512 
1.4853 
1.5907 
0.9601 
36.521 
38.0 
0.0041 
25 
0.0503 
0.9560 
1.5395 
0.9324 
1.3120 
1.3827 
0.9408 
31.769 
33.8 
0.0086 
30 
0.0797 
0.9079 
1.1444 
0.8969 
1.0818 
1.1062 
0.9014 
27.164 
30.1 
0.0152 
35 
0.0919 
0.8356 
0.8128 
0.8420 
0.8365 
0.8116 
0.8352 
22.822 
27.3 
0.0200 
40 
0.1003 
0.7588 
0.5731 
0.7794 
0.6311 
0.5650 
0.7559 
18.845 
24.9 
0.0235 
45 
0.1091 
0.6827 
0.3831 
0.7148 
0.4593 
0.3588 
0.6721 
15.275 
22.7 
0.0239 
50 
0.1243 
0.6082 
0.2199 
0.6560 
0.3228 
0.1948 
0.5962 
12.104 
20.3 
0.0230 
55 
0.1418 
0.5326 
0.0653 
0.6048 
0.2127 
0.0626 
0.5313 
9.285 
17.5 
0.0255 
60 
0.1732 
0.4571 
0.0861 
0.5530 
0.1064 
0.0650 
0.4676 
6.788 
14.5 
0.0335 
65 
0.2191 
0.3779 
0.2493 
0.4918 
0.0163 
0.2124 
0.3954 
4.631 
11.7 
0.0502 
70 
0.2802 
0.2951 
0.4354 
0.4119 
0.1781 
0.4066 
0.3072 
2.874 
9.4 
0.0718 
75 
0.3586 
0.2124 
0.6553 
0.3178 
0.3819 
0.6513 
0.2137 
1.572 
7.4 
0.1013 
80 
0.4475 
0.1362 
0.9235 
0.2173 
0.6408 
0.9622 
0.1274 
0.719 
5.6 
0.1480 
85 
#N/A 
0.0753 
1.2542 
0.1201 
0.9959 
1.3887 
0.0586 
0.255 
4.3 
0.2097 
The logit transformations of the proportions surviving appear in column 4 of Table 6. 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 6 appears in column 6 of Table 6. 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 6 over the range of ages chosen by the user (45 and 80 in this example), namely 0.1928 and 1.2008 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 6. 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 6. 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 6, are then calculated from the fitted life table. These numbers are then used to produce the smoothed mortality rates which appear in column 10 of Table 6. For example, for age 80
The life expectancies which appear in column10 of Table 6 are the numbers in column 9 divided by the numbers in column 8. For example, the life expectancy at age 65 is
The estimate of completeness is 94 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 (in the SEG_South Africa_females [7] workbook) gives an estimate of completeness of 93 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 as to validate the estimates.
A second check on the results is to compare them with the result from the Generalized Growth Balance method [3] (in the GGB_South Africa_males [8] workbook), which estimated the completeness of death reporting over the age range 5 to 84 to be 92 per cent. This again supports the result.
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 51.9 per cent, while the estimate of _{45}q_{15} from the WPP for the period 20002005 is 52.9 per cent, again suggesting no reason to question the results.
As a matter of interest, application of the Preston and Coale method [1] to these data (estimating the population in the middle of the period as that average of the two survey populations) provides an estimate of completeness, using the same age range, of 84 per cent. Increasing the minimum age of range of the data used to determine delta to 35 increases the estimate to 86 per cent, still somewhat lower than the estimate of 94 per cent produced above.
Inspection of the estimates of completeness (Figure 1) suggests that the completeness of death reporting appears to fall steadily with age from about age 55, which is consistent with migrant workers retiring from urban areas to rural areas, where completeness of registration was lower. Since these estimates were produced using the estimate of delta produced by application of the Generalized Growth Balance method [3] and it is entirely plausible that people have retired from urban to rural areas, reducing delta to produce a more level set of estimates is inappropriate.
Since migration has been taken into account, the falloff in estimates of completeness at the younger ages is probably due to the opposite of what is happening at the older ages, namely, young people moving from rural to urban areas to find employment. It would be wrong, therefore, to allow estimates at these ages to influence the estimate of overall completeness unduly.
The lack of smoothness in the series of the ratios of
is determined by the estimates of the population from the census and survey, and not from the deaths. Thus, the erratic nature of this series is probably indicative of errors due to relative undercounting in particular age groups and/or age misreporting in the census or survey population estimates.
Generally there are two sorts of problems with the death 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.
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.
The data are subject to four potential problems:
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.
In all such cases, one should avoid the temptation of adjusting delta to produce a level sequence of the ratios, and ensure that the estimate of c is determined over an age range which excludes the ages where distortions exist.
In practice both the sequences of
and
are affected by violations of the assumptions. However, part of the power of this technique is that most of the typical violations of assumptions produce fairly distinctive characteristic deviations from the expected horizontal plot and in certain circumstances these patterns are interpretable. The following are examples:
(a) Incorrect estimate of relative coverage of the censuses: If δ is too high the sequences fall nearly linearly with increasing age towards the underlying value of completeness and vice versa, as can be concluded from inspection of equation (1) below. The effect is greater for
than for
.
(b) Exaggeration of reported age: Typically, relatives reporting deaths exaggerate the person’s age at death more than living individuals reporting their own ages. This produces rising sequences of points which are imperceptible up to the age at which exaggeration begins, followed by a sharp upward curve thereafter. Again, it can be seen from inspection of Equation 1 below, that age exaggeration leads to an increase in the number of deaths in the older age categories. In addition, transfers within an age category lead to those deaths being multiplied by a larger exponential term, although this effect is far smaller. Although such a pattern would also be produced by rising completeness in death registration with age beyond a certain age there appears to be no evidence of this in practice (Preston, Coale, Trussell et al. 1980).
(c) Age misstatement in the population estimates and agespecific miscounting: This is exhibited by an erratic sequence of the ratios over the age span. Sinceis cumulative in form, it tends to follow the age distribution of the population quite closely and hence, if there are zigzags, it is likely that the peaks are associated with inflated population estimates and the troughs with deflated ones. If these fluctuations are independent of age they will not distort the estimate of completeness particularly. However, if they are systematic, for example due to unaccounted for migration beneath a certain age, it may be desirable not to include these points in estimating the completeness.
The examples below use the same data as used in the SEG_South Africa_males [4] and SEG_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 7.
Table 7 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] workbooks.
Applying the Synthetic Extinct Generations method to these data for males using the estimate of relative incompleteness of census coverage (delta) derived from the application of the Generalized Growth Balance method [3] to these data, SEG_South Africa_males_hhd [11], suggests that these estimates of the number of deaths are more or less as completely reported as the vital registration. However these data estimate _{45}q_{15} at 53.9 per cent, which although similar, is slightly higher than the estimate produced using registered deaths. Applying the Synthetic Extinct Generations method to these data for females, SEG_South Africa_females_hhd [12], suggests that the deaths of women reported by households are far less complete than the registered deaths and estimates _{45}q_{15} at 49.3 per cent. This is 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 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 8. 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 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.
Table 8 Ratio of estimates of deaths derived from deaths reported by households to the expected numbers of deaths, South Africa

Males 

Females 


Age 
Reported 
Expected 
Ratio 
Reported 
Expected 
Ratio 
04 






59 
22,683 
16,979 
134% 
22,995 
14,575 
158% 
1014 
16,462 
12,224 
135% 
15,173 
10,349 
147% 
1519 
38,013 
27,784 
137% 
35,666 
26,874 
133% 
2024 
74,934 
59,946 
125% 
95,993 
84,611 
113% 
2529 
124,403 
112,129 
111% 
152,718 
154,437 
99% 
3034 
150,792 
158,796 
95% 
166,488 
170,680 
98% 
3539 
159,016 
159,137 
100% 
137,837 
141,399 
97% 
4044 
140,172 
148,269 
95% 
111,910 
115,746 
97% 
4549 
120,016 
131,988 
91% 
85,284 
93,408 
91% 
5054 
118,989 
121,242 
98% 
76,941 
81,793 
94% 
5559 
97,977 
105,641 
93% 
57,353 
72,131 
80% 
6064 
88,088 
98,089 
90% 
69,220 
78,877 
88% 
6569 
80,451 
90,359 
89% 
67,007 
86,099 
78% 
7074 
72,827 
79,663 
91% 
69,536 
93,404 
74% 
7579 
59,632 
69,665 
86% 
61,942 
88,314 
70% 
8084 
45,365 
52,533 
86% 
58,410 
77,084 
76% 
85+ 
51,779 
50,387 
103% 
83,753 
108,002 
78% 
In 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 produce estimates of _{45}q_{15} of 58.1 per cent for males and 55.6 per cent for females. Unlike the previous estimates, these are estimates of mortality in the year preceding the second census/survey and therefore might 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.
Referring to this method as the Synthetic Extinct Generations is somewhat misleading, since it is not, as was the case with the method proposed by Preston and Coale, et al (1980), derived from the idea of extinct generations originally proposed by Vincent (1951).
Instead the method relies on a reconstruction of the past rather than projecting the future. The generalised form of this reconstruction is outlined in the seminal paper by Preston and Coale (1982). In order to derive the expression for N(y,t), the population at time t aged y exactly, in terms of deaths and growth rates at time t, we start with an expression for the number of deaths at age x>y and ignore migration for simplicity. (Migration can be included simply by deducting the rate of net immigration (i.e. immigration less emigration) from the growth rate. That is replacing r(a,t) by r(a,t) i(a,t) where i(a,t) represents the rate of net immigration at age a at time t). ^{}
or
Thus, it is possible to derive an estimate of the population at each age based on the agespecific numbers of deaths over a particular interval and the agespecific population growth rates. Comparison of these estimates of the population to the estimates derived from censuses gives an estimate of completeness of the deaths relative to that population.
Since the data one typically works with are subject to age misstatement, in practice one usually works with data grouped into fiveyear age groups.
Thus, assume that in practice one has data on the following: the number of reported deaths over a number of years, from times t_{1} to t_{2}, in fiveyear age groups,
, up to an open interval at age A,
; and the number of people in the population at each of times t_{1} and t_{2}, in the same age groups reported by the censuses,
up to
(where t = either t_{1} or t_{2}). These data can then be used to apply the method by computing
and
, and approximating
by
and
by
As suggested by Bennett and Horiuchi (1981), a computational form of Equation 1 can be derived, namely that
where
represents the number of people in the population who turned x between the census at time t_{1} and the census at time t_{2}, and
represents the average annual growth rate of the population aged x to x + 4 last birthday between times t_{1} and t_{2}.
Bennett and Horiuchi (1981, 1984) suggest using the age groupspecific growth rates to improve both the
at the older ages and
, where A is the age at the start of the openended age interval. They suggest calculating
as follows:
where
represents the reported deaths aged A and older, and
represents life expectancy at age A.
They also suggest that in order to allow for the curvature, particularly at the older ages, Equation 2 could be modified as follows:
where
In addition to this, they suggest that over the age of 60 the
be approximated by “imposing a stable population curve over the fiveyear span and then determining the area under the curve accordingly” (Bennett and Horiuchi 1981: 210). However, in practice the data are rarely accurate enough to warrant such a refinement, and it seldom makes much difference to the estimate of completeness.
In practice, in order to correct, to some extent, for the effects of digit preference in age reporting and also to make the death data consistent with population data for conventional fiveyear age groups, it is usual to compute
. Furthermore, since the sequence of
ratios (or even
as suggested by Bennett and Horiuchi (1981)) is usually still somewhat erratic because of age misreporting and differential omission of persons in particular age spans, it is usual to assume that the percentage reported is roughly constant with respect to age for ages greater than, say, 10. One estimates this fixed proportion, c, by either the mean or median of the values of
over a representative span of ages (after, if necessary, correcting the age groupspecific growth rates for the differential completeness of the two censuses). Allowing for differential completeness of the two censuses is achieved by adding a constant factor,
, to the age groupspecific growth rates derived from the reported population numbers to produce a ‘flat sequence’^{ }of
.
To see this, suppose
and
. Then
where
Thus
, where t is the length of the intercensal period, gives an indication of the differential completeness between the two estimates of the population used to estimate the age group specific growth rates.
The sequence of
values is usually plotted together with that of
, where
. The latter ratio tends to be more stable and assists with interpretation of the data.
If the ages were recorded accurately and the assumption of constant census coverage by age held (not a very likely situation), 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 applying a truncated version of the method which eliminates from consideration deaths and population aged x + n and older. This adaptation could, for example, be applied to vital registration data where completeness might fall off above retirement age if people retired from urban to rural areas. It could also be applied where deaths reported by households where household might disintegrate on the death of the last adult. However, unless x+n is high this method is unlikely to be very robust. Analogous adaptation of the Generalized Growth Balance method [3] is easier and seems to be a little more robust.
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. They concluded, with perhaps unrealistic assumptions about migration, that the methods were not particularly reliable.
Bennett NG and S Horiuchi. 1981. "Estimating the completeness of death registration in a closed population", Population Index 47(2):207221. doi: http://dx.doi.org/10.2307/2736447 [13]
Bennett NG and S Horiuchi. 1984. "Mortality estimation from registered deaths in less developed countries", Demography 21(2):217233. doi: http://dx.doi.org/10.2307/2061041 [14]
Blacker J. 1988. An Evaluation of the Pakistan Demographic Survey. Karachi: Pakistan Federal Bureau of Statistics. http://dx.doi.org/10.2307/2061041 [14]
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 [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, 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 [17]
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 [18]
Preston SH, AJ Coale, J Trussell and M Weinstein. 1980. "Estimating the completeness of reporting of adult deaths in populations that are approximately stable", Population Index 46:179202. doi: http://dx.doi.org/10.2307/2736122 [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. 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 [20]
Vincent P. 1951. "La mortalite des vieillards", Population 6:182204. doi: http://dx.doi.org/10.2307/1524149 [21]
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