The hard questions soft drinks raise

In March, the British government announced that it intends to impose a tax on sugary drinks from 2018 to tackle childhood obesity. Whether the tax, which will be debated this summer, achieves its public-health goals depends on the details, and on rigorous evaluation of its effects.

The United Kingdom is not alone in worrying about the global rise in obesity-related ailments like diabetes and cardiovascular diseases - costly conditions that can lead to significant disability and early death. Many countries have, or are considering, imposing taxes on unhealthy foods and drinks - especially those to which sugar has been added. For example, Chile has an 18 percent tax on high-sugar drinks, France taxes drinks with both added sugar and artificial sweeteners, and Hungary taxes food and drinks with high sugar, salt and caffeine content. And Philadelphia in Pennsylvania recently became the largest US city to impose a tax on sweetened drinks.

These food taxes are one of the most effective behavioral-change levers available to policymakers: price. But it would be premature to conclude that higher prices necessarily lead to lower consumption and thus better health outcomes. The effectiveness of a tax depends on how it is designed, and how consumers and the food industry respond to the incentives it creates.