Behaviour Change

PROPAGANDA FOR CHANGE is a project created by the students of Behaviour Change (ps359) and Professor Thomas Hills @thomhills at the Psychology Department of the University of Warwick. This work was supported by funding from Warwick's Institute for Advanced Teaching and Learning.

Wednesday, February 19, 2014

Last but not Least: The last cookie in the jar is actually the best!

Do you ever get home from a shopping trip, lay your items out on your bed or put them on in front of the mirror with full intention of parading them around the house before asking yourself “WHY did I buy that?” You then stuff them back into the shopping bag, dump them somewhere on the floor and tell yourself that tomorrow you will return them (even though you know this will never happen). I frequently find myself in this situation and I’ve noticed that this is often after a sale. “Why?” I hear you ask, “sales are great, everything’s cheap”, yet the very concept of a sale is the ‘impulse buy’ as you are very aware that leaving the item and returning tomorrow for it may well mean that it has already been sold. Well, this is scarcity. Brock (1968) came up with commodity theory – the idea that scarcity increases perceived value of a product. Since then, salesmen have caught on, realising that manipulating perceived scarcity of a product will help sell that product.

This has since been empirically tested by Worchel, Lee and Adewole (1975) in an experiment manipulating the scarcity of cookies. Participants, told they were taking part in experiment assessing variables that affect people’s preferences for various foods, were asked to rate cookies on how much they liked them, how attractive the cookie is as a consumer item and how much they thought the cookies should cost. The jar of cookies they were to try one out of either contained 2 cookies (scarce) or 10 cookies (abundant). In the change conditions another experimenter came into the room and either stated that his participants had eaten more cookies than expected (demand) or simply stated that he had picked up the wrong jar (accident) both resulting in the second experimenter swapping a 10 jar for a 2 jar of cookies. In the abundant change conditions these scenarios were reversed so a 2 jar was swapped for a 10 jar of cookies. Participants were either in the ‘high’ or ‘low’ participation condition where they were told that either many people were participating in the experiment or few people were participating. Table 1 shows the results for this study:

Participants rated cookies in the scarce condition as more desirable than those in the abundant condition and furthermore, were rated more valuable when supply of cookies changed from abundant to scarce than simply starting off scarce. The particularly interesting finding, however, was that when cookies became scarce due to high demand they were rated as more desirable than cookies that became scare due to an accident. 

This research suggests that to be a successful cunning salesman the best strategy is to begin with a product in abundance and then manipulate the product to appear scarce due to high demand for the product rather than anything else. And THAT, is why sales are so effective at making us buy stuff we don’t want…


Brock, C. Implications of commodity theory for value change. In A. G. Greenwald, T. C. Brock, & T. M. Ostrom (Eds.), Psychological foundations of attitudes. New York: Academic Press, 1968.

Worchel, S., Lee, J. & Adewole, A. (1975). Effects of supply and demand on ratings of object value. Journal of Personality and Social Psychology, 32(5), 906-914.

Eleanor Silk       Blog 3

1 comment:

  1. Very good, you contextualise the research well with that introduction.


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