On Sugary Drinks, Taxes and Demand Curves

A few days ago, I discovered a blog post on the website of Jayson Lusk (a very good agricultural economist whose work has often guided some of my own economic history research given that most economic history is also agricultural history). The post relates to a study of the implementation of a sugary drink tax in Berkeley to fight obesity.

Obviously, a tax will reduce the consumption of any good. That is pretty axiomatic and all that we need to know is how much. In other words, how elastic is demand. If all things are held constant, the quantity consumed relative to the price change will give you that measure.* However, the study that Lusk pointed too basically shows that we often do not hold everything constant.

The authors of the study point out that when tax is passed, there is generally a debate that occurs beforehand. This generates publicity about the issue. This alters the behavior of consumers because they face more information. This is an effect that must be isolated from that of the tax itself.  That is what the authors do in their papers and they find that a reduction of soft drinks consumption did occur during the campaign and after the tax was adopted but before it was implemented (they rely on on-campus sales of soft drinks at a “major university” which we can assume is UC-Berkeley). Thus, the reduction in consumption preceded the price change. Lusk himself found something similar in a case related to animal welfare. Using a Californian electoral proposition regarding animal welfare in the production of eggs, he found that the publicity surrounding the proposition changed consumer behavior.

Lusk, rightly in my opinion, points out this suggests that information-based policies are probably more efficient than heavy-handed measures like taxes.

But I think there is a deeper point to make. When you inform consumers, you don’t only change the location of the demand, you also change the slope of the curve. If a consumer is made aware of the costs (and benefits) of his consumption that he had not previously considered, he may become more sensitive to the price. Informing people about the ill-effects of sweet drinks might make them more sensitive to the price they pay. Imagine that the information campaign during the Berkeley vote on the tax caused consumption to become more elastic. That means that the tax’s effects is being amplified by the information effect from the publicity. Had the tax been imposed as a surprise, the effect would have been smaller. Basically, Lusk’s presentation of the argument is understating the effects of information-based policies.

* On a tangential point, I would like to remind that people can reduce their consumption of soft drinks without changing their total calorific intake. Indeed, if I am taxed when I consume a soft drink, I can switch to coffee with cream. Thus, pundits often confuse a reduction in soft drinks consumption after a tax as a step in favor of reducing obesity.