  The United Nations (UN) issued official probabilistic population projections
for all countries to 2100 in July 2015. This was done by simulating future
levels of total fertility and life expectancy from Bayesian hierarchical
models, and combining the results using a standard cohort-component projection
method. The 40 countries with generalized HIV/AIDS epidemics were treated
differently from others, in that the projections used the highly multistate
Spectrum/EPP model, a complex 15-compartment model that was designed for
short-term projections of quantities relevant to policy for the epidemic. Here
we propose a simpler approach that is more compatible with the existing UN
probabilistic projection methodology for other countries. Changes in life
expectancy are projected probabilistically using a simple time series
regression model on current life expectancy, HIV prevalence and ART coverage.
These are then converted to age- and sex-specific mortality rates using a new
family of model life tables designed for countries with HIV/AIDS epidemics that
reproduces the characteristic hump in middle adult mortality. These are then
input to the standard cohort-component method, as for other countries. The
method performed well in an out-of-sample cross-validation experiment. It gives
similar population projections to Spectrum/EPP in the short run, while being
simpler and avoiding multistate modeling.
