■ Does the tax raise the price of soda? In theory, the tax could be absorbed by the bottlers or sellers, so that consumers never feel it. Researchers thought the tax would be fully passed through in the form of higher prices, and in Mexico it was.

■ Do increases in the price of soda actually reduce purchases? The research by the University of North Carolina, conducted with the Mexican public health authorities, found that they did. Over the course of last year, there was an average 6 percent decrease in soda sales, and the effect appeared to intensify as the year wore on. By December 2014, the last year of the study, sales were down 12 percent compared with December 2013. The declines were the biggest for lowest-income Mexicans — as large as 17 percent in December — suggesting that it was the prices, and not publicity around the tax, that was making the difference.

■ Did rates of obesity or diabetes fall? This crucial question remains unanswered. It’s possible, for example, that people who stopped buying soda bought apple juice with a similar number of calories from natural sugar. Or maybe they switched to water but ate a lot more ice cream. There’s some science that shows that liquid calories don’t make people full the same way solid ones do — suggesting that the lost calories won’t be fully replaced. But there’s little research on what happens when you change people’s beverage habits over the long term, so it will take years before we know whether a drop in soda drinking translates into actual health gains for Mexicans.

The taxes appear likely to hurt soda makers’ sales. The American Beverage Association, a trade group for the soda makers, has fought strongly against the taxes. The group argues that the taxes would unfairly single out one industry for the obesity crisis, and says that customers will simply find their calories elsewhere.

The beverage group points to earlier studies of soft drink taxes, in the United States and in Europe. In those studies, soda consumption didn’t decline much, and obesity didn’t budge, because people switched to other caloric drinks.

“They just found that folks would just find other ways to get the products or nutrients they wanted,” said William Dermody, a spokesman for the association. “Taxes and bans and restrictions don’t change the behaviors that lead to obesity.”