Amstrup's forecasts were the product of a complex set of assumptions. We could not rate his procedures against 26 relevant forecasting principles because his report did not contain sufficient information. Of the 90 relevant principles against which we were able to rate Amstrup's procedures, 73 were violated. Some of the violations were sufficient by themselves to render the forecasts invalid.

One polar bear expert specified variables, relationships, and inputs. The same expert then made adjustments until the forecasts conformed to his expectations. In effect, then, Amstrup's forecasts were the opinions of a single expert (himself) unaided by forecasting principles. Much research has shown that unaided expert opinions are not valid for forecasting in situations with high complexity and much uncertainty, as is the case with the polar bear population.

Hunter's forecasts were also the product of a complex set of assumptions. Complexity makes errors hard to detect, and when knowledge of the situation is weak, erroneous assumptions multiply and lead to large errors. Hunter's procedures violated 80 out of the 105 principles against which we were able to rate them. Amazingly, Hunter and her colleagues extrapolated the polar bear population nearly 100 years into the future on the basis of five years of data. Even the five years of data were of doubtful validity.

As far as predicting the future of the polar bear population is concerned, the opinions of polar bear experts have no value without the aid of scientific forecasting procedures.

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