statistical annex explanatory notes 153 uncertainty around under-five and adult mortality rates was considerable because of a aucity of survey or surveillance information, wide distributions were sampled but the results were constrained based on estimates of the maximum and minimum plausible values for the point estimate For 55 countries, mainly in sub-Saharan Africa, estimates of life tables were made by constructing counterfactual life tables excluding the mortality impact of the Hiv/ AIDS epidemic and then combining these life tables with exogenous estimates of the excess mortality rates attributable to HIvIAIDS. The estimates were based on back-calculation models developed as part of collaborative efforts between WHO and the Joint United Nations Programme on HIV/AIDS (UNAIDS)to derive country-level epidemiological estimates for HIV/AIDS. In countries with substantial numbers of deaths, estimates of their uncertainty range were also incorporated into the life table uncertainty analysis. ANNEX TABLE 2A Estimates of child mortality are regularly published by various international organiza- tions, including WHO. Footnotes are used to explain the underlying methodology and sometimes include information on the availability of empirical data that underlie the estimates More frequently, however, the reader of the tables is not informed about the source of information. In the current set of tables WHo has made a first attempt to share a brief summary of the underlying empirical information. This should allow the reader to obtain an idea of how much the estimate is based on real data versus assumptions. At this point the tables do not include an assessment of the quality of the data. The estimation process does take the quality of the empirical data into account In the context of the Millennium Development Goals(MDGs), particular attention is paid to the measurement of progress towards reaching Goal 4, to reduce by two thirds the mortality rate among children under five between 1990 and 2015.At coun try level this implies government commitment not only to implement initiatives to improve child health but also to set up a reliable system to monitor such progress Such a system, if implemented, should be able to provide the number of deaths of children under five years of age by sex, age and cause. However, countries with high levels of child mortality are those where there is very little information or none at all especially on trends Annex Table 2a presents the sources and results of information on under-five mortal- ity rates during the last 25 years which are available at WHO. All efforts were made to ensure completeness and accuracy of the information presented, but the table does not intend to be exhaustive. Data collection efforts are summarized for three periods 1980-1989, 1990-1999 and 2000-2003. Only data collected in the most recent pe riod provide new information on the trend in child mortality in the new millennium. In all other cases, the estimates for the MDGs are drawn entirely from projections based on trends derived from empirical data points prior to the year 2000 There are four primary sources of empirical under-five mortality data: vital reg istration(VR), sample registration system(SRS), surveys and censuses. The vital registration or sample registration system provides numbers of deaths by age and sex obtained by direct observation and reporting of individual deaths. These are pro- spectively collected data. In the case of a survey or a census, the empirical data are based on retrospective data. Interviews with mostly the mother or caregiver or head of household provide information on the survival history of children in the householdstatistical annex explanatory notes 153 uncertainty around under-five and adult mortality rates was considerable because of a paucity of survey or surveillance information, wide distributions were sampled but the results were constrained based on estimates of the maximum and minimum plausible values for the point estimates. For 55 countries, mainly in sub-Saharan Africa, estimates of life tables were made by constructing counterfactual life tables excluding the mortality impact of the HIV/ AIDS epidemic and then combining these life tables with exogenous estimates of the excess mortality rates attributable to HIV/AIDS. The estimates were based on back-calculation models developed as part of collaborative efforts between WHO and the Joint United Nations Programme on HIV/AIDS (UNAIDS) to derive country-level epidemiological estimates for HIV/AIDS. In countries with substantial numbers of war deaths, estimates of their uncertainty range were also incorporated into the life table uncertainty analysis. ANNEX TABLE 2A Estimates of child mortality are regularly published by various international organiza￾tions, including WHO. Footnotes are used to explain the underlying methodology and sometimes include information on the availability of empirical data that underlie the estimates. More frequently, however, the reader of the tables is not informed about the source of information. In the current set of tables WHO has made a first attempt to share a brief summary of the underlying empirical information. This should allow the reader to obtain an idea of how much the estimate is based on real data versus assumptions. At this point the tables do not include an assessment of the quality of the data. The estimation process does take the quality of the empirical data into account. In the context of the Millennium Development Goals (MDGs), particular attention is paid to the measurement of progress towards reaching Goal 4, “to reduce by two thirds the mortality rate among children under five between 1990 and 2015”. At coun￾try level this implies government commitment not only to implement initiatives to improve child health but also to set up a reliable system to monitor such progress. Such a system, if implemented, should be able to provide the number of deaths of children under five years of age by sex, age and cause. However, countries with high levels of child mortality are those where there is very little information or none at all, especially on trends. Annex Table 2a presents the sources and results of information on under-five mortal￾ity rates during the last 25 years which are available at WHO. All efforts were made to ensure completeness and accuracy of the information presented, but the table does not intend to be exhaustive. Data collection efforts are summarized for three periods: 1980–1989, 1990–1999 and 2000–2003. Only data collected in the most recent pe￾riod provide new information on the trend in child mortality in the new millennium. In all other cases, the estimates for the MDGs are drawn entirely from projections based on trends derived from empirical data points prior to the year 2000. There are four primary sources of empirical under-five mortality data: vital reg￾istration (VR), sample registration system (SRS), surveys and censuses. The vital registration or sample registration system provides numbers of deaths by age and sex obtained by direct observation and reporting of individual deaths. These are pro￾spectively collected data. In the case of a survey or a census, the empirical data are based on retrospective data. Interviews with mostly the mother or caregiver or head of household provide information on the survival history of children in the household