For that reason, we will take a closer look at these. The United Nations Population Division publishes its projections every two years . The very fact that it publishes a broad spectrum of possibilities should tell the user something. If future world population size could truly be known, only one would be required. The five main series of projections vary considerably.
Most users have a strong tendency to approach projections backwards.
But those are not the questions we should be asking. The answer is simple. At the global level, this is the only source of variation. Often, that makes the task of citing the results far too easy for the user. Just use the middle series.