The purchase intention questions in a traditional Concept Test likely measure desire rather than true intention. Desire is infinite and resources are finite and we should expect that purchase intention questions will over-state demand. A solution to this problem is to ask consumers to choose from multiple products. Such choice tasks have the important advantage of most closely replicating the real world tasks that shoppers perform. For example:
If you saw the following products at these prices when you were next shopping for babyfood, which of these would you buy?
Most commonly, consumers will be presented with a single screen (or piece of paper) containing descriptions of the new product and competitor products in the market segment and their prices. Consumers are asked to select only one of the brands. As they have had to make a choice between all of the available alternatives, the data implicitly takes into account the finite nature of consumers’ resources, and we expect (and often observe) a high correspondence between the proportion of respondents who select a product and the true proportion who buy it in the real world.
Of course, there is something a bit unnatural about such choice tasks, containing one new product and existing products. The poorer the correspondence between the real-world and a question being used to predict real-world behavior, the less accurate we should expect the question to be.[note 1] A solution of sorts to this is to Choice Modeling, as with a choice model all of the alternatives are artificial and thus the problem of one being new is not a source of bias.
Where consumers are likely to change their purchasing in different situations (e.g., meal occasions), or, due to variety seeking, these can be addressed by occasion-cuing the questions (e.g., “thinking about your last trip”, or, “thinking about your last time you went to the football”) or by using Constant-Sum questions (e.g., “thinking of your next 10 purchases, how many of each of these products would you buy?”).
Many choices tasks include an “I would not buy any of these” option. Such descriptions should only ever be included when it is a realistic outcome. As an example, if modelling airline choice, it is clearly realistic to permit a consumer to say they would choose not to fly given the available alternatives. By contrast, if modelling choice of beverage on a hot day, the inclusion of the “none” option is problematic, as in reality the consumer is likely to be forced to choose between the brands in the choice task and may select “none” as a way of signalling that they do not like these brands (even though if presented with only these brands they probably would have actually chosen one of them).
- The extent to which the choice task replicates the real-world environment in which the consumer chooses is referred to as the question’s ecological validity. The most comprehensive discussion of this issue is provided by: Marder, Eric (1997), The Laws of Choice. New York: The Free Press., who does not use the term ecological validity. See: Bateson, John E. G. and Michael K. Hui (1992), "The Ecological Validity of Photographic Slides and Videotapes in Simulating the Service Setting," The Journal of Consumer Research, 19 (2), 271-81. for a more general discussion of ecological validity.