The New York Times and Time Magazine have recently posted interesting articles about two new books that discuss consumer behavior: Chris Anderson’s Free and Ellen Ruppel Shell’s Cheap (see links in The New York Times and Time Magazine).

Both books reference our Hershey’s Kiss experiment that is described in Chapter 3 of Predictably Irrational. If you recall, in one trial of one study we offered students a Lindt Truffle for 26 cents and a Hershey’s Kiss for 1 cent and observed the buying behavior: 40 percent went with the truffle and 40 percent with the Kiss. When we dropped the price of both chocolates by just 1 cent, we observed that suddenly 90 percent of participants opted for the free Kiss, even though the relative price between the two was the same. We concluded that FREE! is indeed a very powerful force.

It’s important to note that we have carried out lots and lots of studies on the effect of FREE!, many of which are detailed in Predictably Irrational. Describing them all, however, would be too much for those who are trying to make just one point abut this effect, so naturally we see authors making choices about which experiments to describe and which ones to leave in footnotes, or not to mention at all. But, some kinds of omissions are made as well — ones that are important for understanding the complexity of the effect.

For example, in one study of FREE!, we tried lowering the price from 2 cents to one cent on the Kiss to see if we observed that same level of increase in demand in the Kiss. We didn’t. In another study we also tried seeing what would happen if we lowered the price from FREE! to negative one cent, and we also didn’t see a difference in behavior. We also tried the experiment on a broad demographic–not just college students, but also on children and older adults.

Personally, I think it is perfectly fine for people to take the main point from some experiments and build on it, but as readers (and writers) we should realize that often there is more complexity to the picture and that before criticizing particular findings, or citing them as supporting evidence, we should keep in mind the nuances.