One of the key problems faced by epidemiologists when making projections about the future spread of HIV is the lack of information about some of the factors which may influence the speed at which HIV spreads amongst different risk groups within the population. Nevertheless it is possible to be fairly confident about some of the key factors which will continue to determine the development of the epidemic simply by looking at past patterns.

In the mid–1980s a series of projections were made from the limited data available at that stage which greatly overestimated the spread of HIV amongst the UK population. These projections created expectations about the development of the epidemic which did not materialise, and have led to claims that the scale of the epidemic was exaggerated in order to win funding.