Traditional treatments of the future almost always contain projections of the known development into the future and prognosis for the future.
The difference between economic projections and prognosis, for example, is that prognosis also has requirements to the conditions of future development.
Prognosis about population is an example of predictions that require certain prerequisites. For the prognosis to be valid, you need immigration and fertility to be determined, so even if the population is currently growing in Denmark, the prognosis might show that the population growth will eventually decline.
A projection on the other hand is just a continuation of the current trends into the future – predicting the future by extending the present with a ruler.
Both methods are good for a quick overview of how things might go, but if you want to work seriously with the future, those two won’t do on their own.
There are too many examples of how wrong it might go, if you only make predictions based on prognosis and projections. In the 80s, for example, a number of experts predicted that the Danish population would fall to 4.2 million people by the year 2040. They then made several reports on the saturation of the housing market in the future – the so-called Ølgaard-reports.
By 2001 we could already see a housing market where there was a much too high demand and a rising shortage of housing in the bigger cities.
The mistake was made in the population prognosis, where the experts had seen the trends in the 1970s and 1980s of people having fewer children, and had continued those trends far into the future. That just wasn’t the case – instead we started having more children.