EPIDEMIOLOGY AND SOCIAL SCIENCE Methods to Estimate the Number of Orphans as a Result of AIDS and Other Causes in Sub-Saharan Africa Nicholas C. Grassly, D Phil* and Ian M. Timæus, PhD† Objective: To derive methods to estimate and project the fraction of children orphaned by AIDS and other causes. Methods: HIV/AIDS affects orphan numbers through increased adult and child mortality and reduced fertility of HIV-positive women. We extend an epidemiologic and demographic model used previously to estimate maternal orphans to paternal orphans. We ac- count for the impact of HIV/AIDS on child survival by modeling the HIV status of the partners of men who die of AIDS or other causes based on data on the concordance of heterosexual partners. Sub- sequently, the proportion of orphans whose parents have both died is predicted by a regression model fitted to orphanhood data from 34 national demographic and health surveys (DHSs). The approach is illustrated with an application to Tanzania and compared with DHS estimates for the years 1992 and 1999. Results: Projections of the number and age distribution of orphans using these methods agree with survey data for Tanzania. They show the rise in orphanhood over the last decade that has resulted from the HIV epidemic. Conclusions: The methods allow estimation of the numbers of children whose mother, father, or both parents have died for countries with generalized heterosexual HIV epidemics. These methods have been used to produce orphan estimates for high-prevalence countries published by Joint United Nations Program on HIV/AIDS, World Health Organization, United Nations Children’s Fund, and US Agency for International Development in 2002 and 2004. Key Words: orphanhood, AIDS orphans, AIDS impact, projections, sub-Saharan Africa (J Acquir Immune Defic Syndr 2005;39:365–375) T he death from AIDS of large numbers of young and middle-aged adults in Africa and elsewhere is producing a parallel rise in the number of orphaned children. Estimates and projections of the numbers of children whose parents have died of AIDS or other causes are needed to inform policy and programmatic decisions. In the past, several agencies have pro- duced estimates of AIDS orphans. These have differed be- cause they have used different definitions and methods and have been based on different assumptions about HIV prev- alence, epidemiology, and natural history. Because estimation of the number of children whose father has died (paternal orphans) or whose parents have both died (dual or double orphans) is relatively complex, some studies only present sta- tistics on children whose mother has died (maternal orphans). 1 Other studies have used simple assumptions to estimate pa- ternal orphanhood that produce approximate estimates. 2 Clearly, the death of children’s fathers as well as their mothers may have an adverse impact on their welfare. More- over, dual orphans are particularly disadvantaged. This article proposes methods for making estimates and projections of maternal, paternal, and dual orphans as a result of AIDS and other causes. An ‘‘AIDS orphan’’ is defined as a child who has at least 1 parent dead as a result of AIDS, and a dual AIDS or- phan is a child whose mother and father have both died, at least 1 as a result of AIDS. Orphan numbers can be calculated from statistics on the deaths of adults by estimating how many children were born to those adults who have died and whether these children remain alive. In countries with an AIDS epidemic, the calculations need to allow for the impact of HIV infection on mortality and women’s fertility while accounting for the transmission of HIV from mother to child and between parents. Key inputs to the estimation procedure are thus AIDS and other-cause mortality data and fertility data by age and sex. These may be derived from demographic projections, census data, and/or household surveys. We make no attempt to derive such data here. The methods we describe have been used by the US Census Bureau to produce estimates of AIDS and other-cause orphan numbers that were adopted by the Joint United Nations Program on HIV/AIDS (UNAIDS), United Nations Children’s Fund (UNICEF) and US Agency for International Development (USAID) since 2002. 3,4 METHODS Maternal Orphanhood The relation between mortality of women and orphan- hood of children in a stable population is well understood. 5–7 It depends largely on the ages of women giving birth. Extension of the analysis to nonstable populations is straightforward. 8 These relations are sufficiently insensitive to variation in most Received for publication January 16, 2003; accepted January 7, 2005. From the *Department of Infectious Disease Epidemiology, Imperial College Faculty of Medicine, St. Mary’s Campus, London, United Kingdom; and †Centre for Population Studies, Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, United Kingdom. Supported by the Joint United Nations Program on HIV/AIDS. Reprints: Nicholas C. Grassly, Department of Infectious Disease Epidemi- ology, Imperial College Faculty of Medicine, St. Mary’s Campus, Norfolk Place, London W2 1PG, United Kingdom (e-mail: n.grassly@imperial.ac.uk). Copyright Ó 2005 by Lippincott Williams & Wilkins J Acquir Immune Defic Syndr  Volume 39, Number 3, July 1 2005 365