Insightology

In a series of classic studies done in the 1960's, the Swiss developmental psychologist Jean Piaget showed how children can misperceive volume. When colored liquid was poured from a taller cylinder to a shorter wider cylinder, they thought the volume of liquid had decreased. These primary school children were using only the height of the container when making volume judgments and were hence making mistakes. Ah, you say, they are children and are naive enough not to understand that more than height goes into determining the volume of liquid in a container. Full grown adults would never make that mistake. Why, if such height based illusions existed, wouldn't restaurants routinely use tall thin glasses to pour your drinks, rather than short wide glasses? Well.         

In a series of experiments conducted in the late 90's two researchers (Raghubir and Krishna) showed that people use the height of a container (elongation) to judge its volume. This is true even for frequently purchased and used packages that people are familiar with. Not only are such judgments made, people even choose taller glasses more often. Further, when it comes to actual drinking, they tend to drink more from shorter glasses, because they think they are drinking less.  So clearly, the height based misperceptions also influence actual behavior. But are these effects likely to exist even if people pour their own drinks? That is what another researcher (Wansink) set out to test with a series of experiments.

In the first experiment, 15 year old children in a camp were given either taller, thinner glasses or shorter, wider glasses to pour juice. If the children perceived the taller glasses to hold more, then to compensate, they should be pouring more into the shorter glasses. Indeed this is what happens. The children poured 75% more juice into the shorter, wider glasses, but they perceive themselves as having poured less.  Not only that, they even consume more from the shorter glasses, as a result. The same result is seen when the experiment is repeated with adults.

Okay, you say, but what about experts? Surely they don't make mistakes such as these, do they? To test this, Wansink conducted an experiment with bartenders in Philadelphia. Bartenders were asked to pour the well established standard level of alcohol for four drinks and for further clarity the amount (1.5oz) was explicitly mentioned. Even though the bartenders had on average 5years of experience, they poured 27% more into short, wide glasses than into tall, slender glasses. The effect was not as pronounced among the more experienced bartenders, but was still there.           

What can we conclude from this? Height based misperception of liquid volume surely exists and depending on who you are (restaurant or bar owner, consumer, parent of children, doctor, nutritionist etc) you could affect behavior just by your choice of glass.    

The first study was conducted by Priya Raghubir, currently Professor of Marketing at the University of California at Berkeley and Aradhna Krishna, currently the Isadore and Leon Winkelman Professor of Marketing at the University of Michigan. The second study was conducted by Brian Wansink, the John Dyson Professor of Marketing and Nutritional Science at Cornell University.