A new study of how taxes might be used to curb consumption of sugary drinks suggests that applying a tax based on the amount of calories contained in a serving rather than its size would be more effective.

The study, financed by the Robert Wood Johnson Foundation, which has long advocated taxing sodas and other sugary drinks as part of its efforts to reduce childhood obesity, found that consumption of calories in drinks would drop 9.3 percent if a tax of four-hundredths of a penny for every calorie was added to the price, but fall by just 8.6 percent under a tax of half a cent for each ounce in a can or bottle.

A calorie-based taxing system would also be fairer to consumers, said Chen Zhen, a research economist at the food and nutrition policy research program at Research Triangle Institute and the lead author of the study.

“It provides a better incentive to the consumer to switch to lower-calorie drinks, which would be taxed at a lower rate than higher-calorie drinks,” Dr. Zhen said. “One of the concerns about taxing ounces of sugar-sweetened beverages is that consumers are paying the same tax whether they buy 12 ounces of a drink with 150 calories or 12 ounces of a drink with 50 calories.”