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Human Behavior Is Shaped by External Factors:
The Influence of Container Size and Shopping Baskets

Takeshi Moriguchi
Professor, Faculty of Commerce, Waseda University

Human behavior is influenced by various external factors. Physical capacity is one of these. Cornell University Professor Brian Wansink has examined the effect of physical capacity (referred to here as container size) on the amount of food people eat in experiments like the one discussed below (B. Wansink (2006), Mindless Eating: Why We Eat More Than We Think). In this experiment, he provided free soft drinks and popcorn to people attending a movie starting at 1:05 on a Saturday afternoon. The moviegoers were given popcorn in one of two sizes: medium or large. Through the experiment, he hoped to determine whether the size of the container would have an unconscious effect on the amount of popcorn moviegoers ate.

There is one detail about this experiment, however, that should be noted. If most of the people had eaten all of the popcorn in the buckets they were handed, the experiment would have been meaningless. So Wansink added a few twists. First, both the medium and large sizes chosen were too big for one person to finish, and a bucket of popcorn was handed out to each person to prevent sharing. Secondly, the experiment targeted people coming to see a movie after 1 p.m. By this time, he reasoned, most people would have already had lunch and not have enough of an appetite to eat all the way down to the bottom of the bucket. Finally, there was something special about the kind of popcorn provided. It wasn’t fresh but 5-day-old popcorn that had been preserved in a sterile state. People would be even less likely to eat all the popcorn if it were stale and unappetizing.

After the experiment was conducted under these conditions and the movie ended, the remaining popcorn left by each person was measured to calculate the amount each had ingested. The results showed that the people handed large-size buckets of popcorn ate an average of 53 percent more than those handed medium-size buckets. In addition, when the people handed the large-size buckets were asked, “Do you think you ate more because you had the large size?” most responded, “No.” Wansink has uncovered the effect of container and spoon size on the amount we eat in many other experiments.

The phenomenon of physical capacity influencing human behavior can also be seen in the shopping behavior of consumers. Nearly twenty years ago, I conducted a study on shopping behavior in collaboration with a convenience store. The study revealed a distribution of purchased items per shopper as shown in Figure 1. Shoppers who bought one item and two items were both around 25 percent of the total. As the number of items increases from three to five, the distribution ratio decreases. In the figure, the data for six items and over are combined together, but in reality the distribution ratio continues to decrease as the number of items increases.

Convenience stores cater to the immediate shopping needs of consumers. Thus, there are not as many customers who come to buy a lot of products at once as you find at supermarkets. The distribution in Figure 1 reflects this feature of shopping behavior in convenience stores.

On the other hand, it is possible that there are physical constraints underlying distribution patterns like those seen in Figure 1. Many people shop at convenience stores without shopping baskets. While shoppers can carry one or two items in their hands, any more than that becomes progressively more difficult to manage. This may impose a limit on the number of items bought.

In fact, if we look at the proportion of people who shopped with a basket at the convenience store in question, we find that they are only 12 percent of the total. If we then calculate the distribution of items purchased by shoppers with baskets, we find that the distribution ratio for 2 items is greater than that for 1 item, the ratio for 3 items is greater than that for 2 items, the ratio for 4 items is greater than that for 3 items, and the ratio of those who bought 6 or more items is close to 50% of the total.

Naturally, one can interpret these findings as reflecting the fact that shoppers who originally came to the store with the intention of buying a lot of items shopped with a basket. On the other hand, however, one can also take the view that those who picked up a basket by chance ended up buying several more items than they otherwise would have. Both of these factors may contribute to distributions like the one above.

In light of these results, the convenience store chain conducted an experiment in which they placed baskets not only by the entrance, but at several locations within the store to increase the percentage of customers using baskets. In the experiment, the percentage of shoppers using baskets increased. As a result, the store confirmed a rise in overall sales, and the chain implemented these measures in all their stores. As in the popcorn example mentioned above, the results demonstrate that physical capacity influences human behavior.

Our behavior is influenced by external factors like physical capacity without us realizing it. Conversely, this also means we can control our behavior by altering these external factors. We unintentionally eat, drink, and buy too much. Those of us, including myself, who have many opportunities to reflect on such mistakes, may need to consider taking control of the external factors that influence our behavior.

Takeshi Moriguchi
Professor, Faculty of Commerce, Waseda University

Professor Moriguchi received a B.A. in Economics from the Department of Economics, School of Political Science and Economics, Waseda University, followed by a Ph.D. in Engineering from the Department of Industrial Engineering and Management, Graduate School of Science and Engineering , Tokyo Institute of Technology. After working at organizations like Rikkyo University, he assumed his current position in 2005. He has been serving as the Dean of the Graduate School of Commerce since September 2012. He has held positions such as President of the Japan Association for Consumer Studies and Vice President of the Japan Society of Marketing and Distribution. His major publications include Analyzing the Effects of Sales Promotion [Puromoshon Koka Bunseki] (Asakura Publishing), Consumer Behavior Theory: From Consumer Psychology to Neuromarketing [Shohisha Kodoron: Shohisha Shinri kara Nyuromaketingu made] (co-authored; Yachiyo Shuppan), Introduction to Marketing Science [Maketingu Saiensu Nyumon] (co-authored; Yuhikaku), and The Reality of Sales Promotion [Serusu Puromoshon no Jissai] (coauthored; Nikkei Bunko).