One was Seattle, the other Mukono, a town in central Uganda, where Ms. Bouterse spent a semester.

In each city, she and Ms. Bouterse sought out a local pathway near a major market center, where people often walked to and from stores and other attractions. The researchers identified permanent markers along the path, such as street signs, set about 30 feet apart.

Then Ms. Bouterse positioned herself close to each pathway and simply timed more than 1,700 people as they walked through the marked section and identified them on a checklist by gender, approximate age, any loads they carried, and who else, if anyone, they walked with, including children. (She focused on whichever walker was closest to her as a group passed by.) They did not include people who obviously were walking for exercise.

Finally, she and Dr. Wall-Scheffler compared the two cities’ results.

People in Uganda, it turned out, walked much more quickly than those in Seattle when they were by themselves, their pace averaging about 11 percent swifter than lone walkers in the United States.

But they were slower in groups. Both men and women in Mukono strolled at a more leisurely pace when they were with others, especially children. Their pace when accompanied by children was about 16 percent slower than when they were alone, whether they carried the children or walked beside them.

The opposite was true in Seattle. There, people sped up when they walked with other people. Men were particularly hurried when walking with other men, but both men and women increased their pace if they had children in tow. Their average walking speed when they carried or accompanied children was about 20 percent speedier than when they walked alone.

This was an observational study; the researchers did not interview the walkers, so it is impossible to know what motivated them to walk as they did.

But Dr. Wall-Scheffler has theories.

“It seems plausible that people in Uganda use their time when they are walking in groups to socialize and bond,” she says, particularly with children. So they walk slowly.