A social science passage at pace

1Ask a group of shoppers why the milk is almost always in the back corner of a grocery store, and most will give the same answer. The store, they say, wants you to walk past hundreds of other products on your way to the one thing you came for, in the hope that a box of crackers or a bag of oranges will find its way into your cart. It is a tidy explanation, and it has the appeal of seeming slightly sneaky. It is also, according to many people who have worked in the grocery business, only part of the story.

2Their version begins with the delivery truck. Milk arrives several times a week in large refrigerated loads, and every minute it spends out of the cold shortens the time it can stay on a shelf. A busy store may sell hundreds of gallons in a single day, so the cases must be refilled again and again. Most stores receive their deliveries at a loading dock in the back of the building, so placing the dairy cases along the back wall lets workers move milk from the truck to the walk-in cooler and then to the shelves with the shortest possible trip. Put the milk at the front, these insiders point out, and every crate would have to be wheeled through the length of the store, past shoppers and through the aisles.

3History supports the delivery account as well. Before the middle of the twentieth century, many grocery stores kept their goods behind a counter, and a clerk fetched each item a customer asked for. Layout hardly mattered to shoppers, who never walked the floor. When self-service stores spread, owners built them around the equipment they already needed, and the heavy refrigerated cases went where the deliveries came in. In some early self-service stores, the dairy case backed directly onto the cold storage room, so that clerks could restock it from behind without ever entering the sales floor. The placement, in other words, was settled for practical reasons before anyone had studied how shoppers move.

4That study came later, and it has given the popular explanation some real support. Researchers who track shoppers’ paths, sometimes by following them with a clipboard and sometimes by attaching small sensors to carts, have found that most people do not walk every aisle, even when they have plenty of time. Instead, they tend to circle the outer edge of the store, where fresh foods are usually kept, and dip into only a few of the center aisles. Shoppers who make a quick trip for one or two items often spend more than they planned, and stores are well aware of it. Some managers say that once they understood these patterns, they placed new products and seasonal displays along the route to the dairy case on purpose.

5So which explanation is right? The fairest answer is that the two describe different moments. The delivery account explains why milk ended up in the back in the first place; the shopping account explains why stores have little reason to move it now. A layout chosen for the convenience of workers turned out to suit the store’s sales as well, and a business seldom changes an arrangement that serves it twice.

6The case of the milk carries a broader lesson about explanations of this kind. When a pattern benefits someone, it is natural to assume it was designed for that benefit. Sometimes it was. Often, though, the benefit was discovered after the fact, and the pattern was first shaped by something far less interesting, such as where the trucks happened to park. Asking where a pattern began, and not only whom it helps, is often the quickest way to tell the two cases apart.

1Ask a group of shoppers why the milk is almost always in the back corner of a grocery store, and most will give the same answer. The store, they say, wants you to walk past hundreds of other products on your way to the one thing you came for, in the hope that a box of crackers or a bag of oranges will find its way into your cart. It is a tidy explanation, and it has the appeal of seeming slightly sneaky. It is also, according to many people who have worked in the grocery business, only part of the story.

2Their version begins with the delivery truck. Milk arrives several times a week in large refrigerated loads, and every minute it spends out of the cold shortens the time it can stay on a shelf. A busy store may sell hundreds of gallons in a single day, so the cases must be refilled again and again. Most stores receive their deliveries at a loading dock in the back of the building, so placing the dairy cases along the back wall lets workers move milk from the truck to the walk-in cooler and then to the shelves with the shortest possible trip. Put the milk at the front, these insiders point out, and every crate would have to be wheeled through the length of the store, past shoppers and through the aisles.

3History supports the delivery account as well. Before the middle of the twentieth century, many grocery stores kept their goods behind a counter, and a clerk fetched each item a customer asked for. Layout hardly mattered to shoppers, who never walked the floor. When self-service stores spread, owners built them around the equipment they already needed, and the heavy refrigerated cases went where the deliveries came in. In some early self-service stores, the dairy case backed directly onto the cold storage room, so that clerks could restock it from behind without ever entering the sales floor. The placement, in other words, was settled for practical reasons before anyone had studied how shoppers move.

4That study came later, and it has given the popular explanation some real support. Researchers who track shoppers’ paths, sometimes by following them with a clipboard and sometimes by attaching small sensors to carts, have found that most people do not walk every aisle, even when they have plenty of time. Instead, they tend to circle the outer edge of the store, where fresh foods are usually kept, and dip into only a few of the center aisles. Shoppers who make a quick trip for one or two items often spend more than they planned, and stores are well aware of it. Some managers say that once they understood these patterns, they placed new products and seasonal displays along the route to the dairy case on purpose.

5So which explanation is right? The fairest answer is that the two describe different moments. The delivery account explains why milk ended up in the back in the first place; the shopping account explains why stores have little reason to move it now. A layout chosen for the convenience of workers turned out to suit the store’s sales as well, and a business seldom changes an arrangement that serves it twice.

6The case of the milk carries a broader lesson about explanations of this kind. When a pattern benefits someone, it is natural to assume it was designed for that benefit. Sometimes it was. Often, though, the benefit was discovered after the fact, and the pattern was first shaped by something far less interesting, such as where the trucks happened to park. Asking where a pattern began, and not only whom it helps, is often the quickest way to tell the two cases apart.