Halal and his colleagues acknowledge that forecasting is inexact. They have greater confidence about nearer-term technologies such as videoconferencing, which they see coming into routine use in six years. History is replete with examples of futurists who got it wrong. The most famous may be Thomas Malthus, an economist who predicted 200 years ago that the Earth could not sustain an ever-growing population, and that famines were inevitable. That pulled the rug out from under the forecast.
Futurists have several methods for gathering their information.
Halal and his co-authors, graduate students Michael D. Kull and Ann Leffmann, drew up their list by examining current trends to see which technologies appeared most promising. The answers were averaged to get a year that serves as a best estimate for when the technology will start to have a large impact in society. Halal acknowledges that by looking at what is being discussed now, it is easy to miss potentially revolutionary technologies. A century ago, for example, urban planners decided that New York had reached the limit of its growth because it would be unable to handle the manure generated by an expanding horse population. They didn't imagine the automobile.