After park visits gradually increased on the course of half a century, in 1988 a sudden decline had began and it never stopped. But why is this going on? Why are people going less and less to parks?

Oliver Pergams, a University of Illinois at Chicago ecologist, took a "don't think, just compute" approach to the problem. He took into consideration a large number of possible factors from playing video games to rising oil prices, to the rise in foreign travel, to crowding of parks, to family income etc. Then he performed a statistical analysis of the data, called multilinear regression, which is capable of determining which factors are most linked to the problem in question - in this case parks visits.

"Many of the variables were highly significantly correlated with this decline in national park visitation," said Pergams. "Multilinear regression apportions which variables are the most significant in affecting the outcome."

The result was that video games, home movie rentals, going out to movies, Internet use, and rising fuel prices explained almost 98 percent of the decline! "It's fairly stunning," he said, although these methods prove only the correlation between factors and not causal relations. In other words it's possible that, for instance, both the decline in parks visits and the rise in home movie rentals to be caused by some other unknown factor.

"This is no smoking gun," Pergams said. "We're showing statistically that the rise in use of these various types of media, as well as oil prices, is so highly correlated with the decline in national park visits that there is likely to be some association."

Pergams ruled out many variables that one might have thought to be more relevant than video games, such as family income, age, the recent rise in foreign travel, or crowding in the parks. However, these variables are not correlated as strongly as home entertainment and fuel prices.

"My concern is that young people are simply not going outdoors or to natural areas, but are instead playing video games, going on the Internet or watching movies," Pergams said. "My longer-term concern is that I don't see how this trend, if it is in fact true, could be good for conservation efforts. But if the trends are correct, perhaps public awareness will lead to some solutions."