"It's well-known that in choosing a destination for shopping, travel time is the number-one factor," said Jean-Claude Thill, associate professor of geography and author of the study.

But, Thill said, what had never been studied is whether shoppers base these decisions on free choice or time constraints.

"My conclusion is that there is differentiation between choice and constraint, and it is most present when you compare genders," said Thill, who will present results of his research Saturday at the annual meeting of the Association of American Geographers.

The study examined the shopping decisions of 700 men and women living in urban and suburban locations in the Minneapolis/St. Paul area.

The results showed that on average, women will travel six miles to shop, while men will travel an average of 6.5 miles to shop, a small, but statistically significant difference, Thill said.

Women, he noted, tend to have less time available to shop because their "activity space"-the territory an individual uses for daily activities-is more crowded.

"Women have work and household activities to perform and a limited amount of time," he said. "That limits the geographical reach within which they will shop.

"Men, on the other hand, have more discretionary time," he said, "so when they decide to shop-and they do shop less frequently than women-they tend to travel longer distances."

The findings have implications for regional planning and, particularly, for developers of retail establishments, said Thill.

"Retailers want to attract customers from as far away as possible," he said. "But that perspective is based on the assumption that overcoming distance is limited to free choice. The retailer thinks 'If we can convince people to travel far by being an attractive place to shop, they will come.'"

This perspective, a sort of "build-it-and-they-will-come" model, completely misses the fact that customers, particularly female customers, are constrained in their shopping decisions, said Thill.

"It's the wrong model," he said. "If you have plenty of time, you're likely to base your decision on your like or dislike for a particular store. You'll choose a place you prefer to shop. But if you only have a half-hour as your constraint, then a 20-mile trip isn't feasible.