Advisors are natural-born skeptics. So can we trust that the demographic projections used by government agencies are accurate? After all, there's a long history of "experts" who have made wildly inaccurate projections about the future.
The most famous fail of demographic prognosticators was Thomas Malthus, who in 1798 published his "Essay on the Principle of Population," in which he argued that the world's food supply, in particular the amount of arable land, would not keep up with its population growth. Simplifying, Malthus was wrong on the demographics because the industrial revolution increased trade, which increased food supplies, and economic growth improved living standards, which then could accommodate more people.
In the 1970s, similar fears were raised about the lack of food for a ballooning world population, but again technology came to the rescue in the form of the "green revolution" in agriculture.
Yes, government policies and that favorite of dystopian novels and movies, epidemics, can change demographic projections, as was the case with the Black Death in Europe in the Middle Ages or, more recently, China's one-child policy. Many studies have shown that increased education, starting with literacy and particularly among women, eventually lead to lower and thus more sustainable birth rates.
As for the Census Bureau — and the Social Security Administration, for that matter — the demographers projecting future populations are very careful in their calculations. In the case of Social Security funding, the trustees always present three different projections to give policymakers a range of possible outcomes based on potential changes to revenue and benefits.
