We often estimate how much we should consume of a product based on aspects of its physical shape. If a product looks incomplete, we’re likely to incorrectly see it as having less value and so consume more of it. (e.g. Wansink, 2006).
Could I take your attention for just a moment?
Now, picture in your mind two sandwiches. These sandwiches are pretty much identical to one another, but the only difference between them is that while one sandwich is left whole, the other one is sliced diagonally in half. Remember that besides the fact that it’s been sliced, the second sandwich is of the same size, quality and quantity as the first. Now, if you were asked to choose one of the two sandwiches, would you have a strong preference for either one?
Unless for some reason you strongly preferred sliced sandwiches, you’d rationally not mind choosing between the two. But in a study, people were placed in an identical scenario as you, and asked the same question. Fascinatingly, researchers found that people were significantly more likely to choose the “complete” (unsliced) version of the sandwich (Sevilla & Kahn, 2014).
But why? Well, when questioned further about their preference, it was found that they felt that the unsliced sandwich ‘had more quantity’ than the sliced one. More generally, research has shown that we humans desire completeness (Hull, 1932; Nunes and Dreze, 2006), and especially aesthetic designs that suggest unity (Veryzer and Hutchinson, 1998). We also feel that incomplete experiences feel ‘unresolved’ (Bieke et al, 2007).
This has led the researchers to conclude that “incompletely” shaped products are assumed to be of lesser quantity than completely shaped ones. We’re also much more likely to purchase complete products over those seen as incomplete. Perceiving that incomplete items are smaller can also influence people to consume more of them. In another study, healthcare professionals were served sandwiches during a lunchtime buffet. Some were given incomplete, sliced sandwiches and others were offered whole ones. Those served sliced sandwiches were more likely to eat more than those served whole sandwiches!
The Completeness Heuristic: Product Shape Completeness Influences Size Perceptions, Preference, and Consumption Article (Sevilla & Kahn, 2014)
Vital Dimensions in Volume Perception: Can the Eye fool the Stomach? PDF (Raghubir & Krishna, 1999)
Mindless Eating: Why We Eat More Than We Think Book (Wansink, 2006)
The goal-gradient hypothesis and maze learning. Article (Hull, 1932)
The Endowed Progress Effect PDF (Nunes & Dreze, 2006)
The Influence of Unity and Prototypicality on Aesthetic Responses to New Product Designs Article (Veryzer & Hutchinson, 1998)
Incomplete inhibition of emotion in specific autobiographical memories Article (Bieke, Adams & Wirth-Beaumont, 2007)