Let me give one example. From 1890 until 1920, Los Angeles population grew by about 11 fold, from 50 thousand to 576 thousand. If one assumed that this would continue, Los Angeles' population 90 years later, in 2010, would have been 576,000*11^3, or about 766 million, which is a shade under the population of the entire Western Hemisphere. Its actual population is around 4 million.
Is this absurd? Of course. But I have been seeing similar forecasts based on similar foundations since I was in college (when a very well-known professor projected that the USSR would have a larger economy than the US by the year 2000). This kind of "analysis" has been driving me crazy for years.