Seattle’s new soda tax goes into effect Jan. 1. And scientists in Seattle will be measuring how it works — in real time.

Jesse Jones-Smith is one of those scientists. She’s an associate professor at the University of Washington medical school. Jones-Smith says sugary drinks lead to obesity, which increases the cost of healthcare.

“The hope is that people decrease their consumption of sugary beverages but buy other things so that businesses don’t suffer.”

Scientists blame obesity for between 6 and 20 percent of U.S. medical costs. Jones-Smith has already been collecting baseline data — from before the soda tax goes into effect. Her hypothesis is that people will buy less sugary drinks — but they’ll make up for it by spending more on other kinds of groceries. That’s what studies have shown in other cities.