_How good are current mortality estiualsw_ _Table 4. Assumedfive-year increments to lif e jetany in United Nations Thpulatioq Division projections_

|"Good" mortality<br>estimatesare based on recent|tifes|||||Females||
|---|---|---|---|---|---|---|---|
|empirical<br>data<br>of<br>high|expec-|||||||
|<br> <br>reliability. The main reasons|tancy|Slow|Middle|Fast|Slow|Middle|Fast|
|for estimates not being of|||_|||||
|good quality are:|55.0-57.5|2.0|2.5|2.5|2.0|2.5|2.5|
||57.5-60.0|2.0|2.5|2.5|2.0|2.5|2.5|
|*<br>The observations|600-625<br>|20<br>|23<br> <br>|25<br>|20<br>|25<br>|25<br>|
|<br> <br>on which the estimates are|..<br>62.5-65.0<br>65.0-67.5|.<br>_2.0_<br>1.5|.<br> <br>_2.0_<br>1.5|.<br>2.3<br>2.0|.<br>_2.0_<br>_2.0_|.<br>2.5<br>2.3|.<br>2.5<br>2.5|
|based are too old.<br>This|67.5-70.0<br>|1.0<br>|1.2<br> <br>|1.5<br>|1.5<br>|2.0<br>|2.3<br>|
|happens mainly in countries<br> <br> <br>|70.0-72<br>72.5-75.0|.5 0.<br>0.5|<br>1.0<br>0.8|1.2<br>1.0|1.<br>1.0|1.5<br>1.2|2.0<br>1.5|
|without<br>reliable<br>vital|75.0-77.5|0.3|0.5|0.8|0.8|1.0|1.2|
|registration. Figure 1 shows<br>|80.0-82.5|0.3|0.4|0.5|0.5|0.8|0.8|
|the number of countries by|82.5-85.0|-|||0.3|0.4|0.5|
|the last period for which|85.0-87.5|--|--|-|0.3|0.4|0.5|
|empirical data were considered|Source:<br>Unit|ed<br>Nat|ions1989|||||
|in<br>construction<br>of<br>the<br>estimates. For estimating the||||||||

current IMR, about 60 percent of considered data were collected in 1985 or later. For life expectancy estimates, this percentage was _55. ("N.A."_ indicates that no empirical data were available, or that the date could not be determined from the source from which the estimate was obtained). From this figure, it appears fair to conclude that estimates of the IMR and life expectancy for most countries are based on up-to-date observations. The currentness of sources is expected to improve further in the next few years, when more of thL. over 100 countries that have planned a census around 1990 are anticipated to release results.

The data on which the estimates are based are of l .or quality or are not represe.itative of the entire population. This could result from underregistration of vital events in registers, incomplete coverage in censuses, defective sampling frames used in surveys, misreporting, etc. For vital registration and census data, the U.N. Statistical Office's publication _Population and Vital Statistics Report_ provides an assessment of their completeness. For survey data, no single evaluation source exists, and data have to be checked for internal consistency and agreement with other sources. T'he U.N. Population Division carries out extensive consistency checks and adjusts numbers which appear incompatible with other information. One of the consequences of such adjustment is that short-term trends are often smoothed out. Many of the surveys conducted in the 1970s and 1980s under the guidance of the WFS and DHS programs are considered to be of good quality.

* Methods used are not appropriate for the data. So-called _indirect estimation techniques,_ which are frequently used to calculate mortality estimates from survey and census data, make assumptions about past trends in fertility and mortality that may not be accurate. Resulting rates may be biased up or downwards. When surveys provide both direct and indirect estimates and the differences are large, further caution is advised. Another assumption, both in calculating the IMR from survcoys or censuses as well as in deriving life expectancy from IMR and/or CDR concerns the appropriateness of model life tables. When the mortality pattern of the chosen model life table is different from the actual mortality pattern, estimates will not be correct.

_7_