Communications of the ACM

Wise experts and powerful machines are no match for chaotic events and human declarations. Beware of their predictions and be humble in your own.

CACM Administrator

The following letter was published in the Letters to the Editor in the November 2012 CACM (http://cacm.acm.org/magazines/2012/11/156596).
--CACM Administrator

In his Viewpoint "Don't Feel Bad If You Can't Predict the Future," Peter J. Denning (Sept. 2012) wrote: "Make sure your models are validated and that their assumed recurrences fit the world you are forecasting. Ground your speculations in observable data..." Hmm... Who validates the models? Physics-based models can be validated, in light of, say, their ability to predict/replicate the results of observable phenomena (such as gravity and inertia); experts in the discipline agree that the assumptions, calculations and/or algorithms, and predicted results match what is seen in the real world. On the other hand, social models rely on assumptions about human behavior, both individual and en masse, that cannot be measured or demonstrated and on predictions that can never be more than "face-validated." That is, "I can't tell you we got the right answer for the right reason; the best I can say is the predicted behavior corresponds to what is observed in real life x% of the time."

This inability to validate the quantification of variables is seen in efforts to model military interactions, as well as social, economic, and political phenomena; for example, no version of either the Lanchester model reflecting the relative strengths of a predator/prey pair or of the many "expanded" Lanchester variants is capable of predicting the outcome of the Battle of Rorke's Drift depicted in the 1964 movie Zulu between British troops and Zulu warriors in South Africa in 1879. Tank on tank, we can predict the odds; add human crews, and things get dicey; witness the dramatically uneven results of combat in Operation Desert Storm when a U.S.-led coalition reversed Iraq's 1991 invasion and nominal annexation of Kuwait. Similarly, one has only to open the newspaper to understand the degree to which we have so far failed to model the American economy sufficiently to suggest effective measures to relieve the ongoing recession. As Denning pointed out, predicting the future is difficult and fraught with danger. Be humble...

Joseph M. Saur
Atlanta, GA

CACM Administrator

The following letter was published in the Letters to the Editor in the November 2012 CACM (http://cacm.acm.org/magazines/2012/11/156596).
--CACM Administrator

I very much agree with Peter J. Denning (Sept. 2012) that one should be humble when predicting anything, especially if the prediction depends on some future human action or decision. Unlike atoms and molecules, humans have free will. More than 60 years ago, the economist and philosopher Ludwig von Mises explored this idea in his monumental book Human Action. More recently, Walter Isaacson's biography of Steve Jobs and Malcolm Gladwell's book Outliers: The Story of Success only reinforced the impossibility of predicting human behavior. Historian J. Rufus Fears wrote: "Nations and empires rise and fall not because of anonymous social and economic forces but because of decisions made by individuals" in the description of his course Wisdom of History. As for Jobs, predicting even the next five minutes would have been futile. Any given human action or even random event might have yielded a totally different technological (or economic or political) world from the one we have today.

Per Kjeldaas
Monroe, LA