Once, twice, six times a grocery shopper

In fact, it turns out that grocery categories such as dessert toppings, motor oil, candles and refrigerated ethnic foods were some of the leading products that lure customers to separate stores.

In the first test of detailed consumer-buying habits by categories at more than one chain store selling groceries, a team of business school researchers led by Washington University in St. Louis found that shoppers weren't monogamist or bigamist but rather polygamist in their choice of outlets.

The vast majority -- a whopping 83 percent -- regularly visited between four and nine chain stores within a year's time to purchase groceries. Of 1,321 households studied among this rich dataset, only 12 stayed loyal to just one store. More than half, at 51.1 percent, went to the average of five to seven different stores. Eighty-eight households, or six of every 100, went to 10 or more.

So much for store loyalty.

Using tracked data from a vendor utilizing a swipe card akin to a loyalty card, the researchers parsed more than $1 million worth of shopping transactions over 53 weeks involving 248 types of products sold at 14 retail chain stores in a large metropolitan market. The study, "Polygamous Store Loyalties: An Empirical Investigation," was published last month in the Journal of Retailing.

What shoppers want in breadth

In the study, researchers found the top 10 categories of products that change a store's attractiveness over its competitors, based on the available breadth of the brand assortment.

1. Motor oil 2. Candles 3. Lighters 4. Refrigerated dips 5. Refrigerated baked goods 6. Dry beans/vegetables 7. Moist towelette 8. Hairspray/spritz 9. Hair accessories 10. Automobile fluids/antifreeze

"Store loyalty was pretty much a given in grocery retail," said senior author Seethu Seetharaman, director of the Center of Customer Analytics and Big Data and the W. Patrick McGinnis Professor of Marketing at Olin Business School. "When people do their shopping, it's the store close to where they live -- location, location, location, like the real-estate mantra.

"Then there is a group of choosy consumers who stop at many stores, shopping for bargains or certain brands or products," he said. "They've been called 'cherry pickers.' " Often, those folks were associated with coupon shoppers.

"That made us do a deeper dive, and we found that people aren't as store loyal as we thought," Seetharaman said. "Clearly, people are polygamous. The majority of people are shopping at six grocery stores."

Consumers tend to shop multiple stores for multiple reasons. In fact, the data showed little loyalty to a single store or handful of stores, but more so to types of products found in a store. Consumers shopped various stories for specific product categories: frozen treats at one grocer, meat and poultry at another, and so on. The researchers called this "intrinsic store-category attractiveness."

Seetharaman was joined in this study by one of his former graduate students, Qin Zhang, assistant professor of business at Pacific Lutheran University, and one of Zhang's former graduate students, Manish Gangwar, assistant professor of marketing at the Indian School of Business. They specified and estimated a statistical model of how consumers fractured their shopping basket and shared their wallet across stores.

The dataset comprised chains that were either traditional supermarkets (Albertsons, Bashas', Food 4 Less, Food City, Fry's Food Store, IGA, Safeway, Trader Joe's and Wild Oats Market), supercenters (Kmart and Walmart) and warehouse clubs (Costco, Sam's Club and Smart & Final). Further evidence of an ever-changing economy in which to purchase grocery, household and health and beauty products: Some of the studied chains have dwindled since the study and no longer service several of their previous states.

What shoppers want in pricing

Here are the top 10 categories of products that change a store's attractiveness over its competitors, based on the degree of price consistency (or lack of price variability) over time. 1. Dessert toppings 2. Refrigerated eggroll/wonton/tortilla wrap 3. Pickles/relish/olives 4. Peanut butter 5. Toothbrush/dental accessories 6. Toilet tissue 7. Cat litter/dog supplies 8. Refrigerated meat/poultry products 9. Snack bars/granola bars 10. Spaghetti/Italian sauce (Source: Seetharaman, Zhang, Gangwar study)

"It's very diffuse," Seetharaman said of consumers' purchases from a larger-than-expected list of stores. "Only 40 percent of their basket is coming from their 'favorite' store."

Some other findings from the research:

• In the market surveyed in particular, Fry's Food Stores emerged as the market favorite by a sizable margin, with Albertson's, Safeway and Walmart next behind it.
• In a large set of categories, a handful of stores competed intensely: Albertson's, Bashas', Safeway and Fry's.
• Warehouse clubs attract loyalty in categories different from the traditional supermarkets and supercenters.
• Family size predicted store loyalty -- the larger families tended toward Fry's or a Walmart Supercenter.
• Income was a somewhat surprising predictor, in that households with higher incomes were more likely to "budget shop" at a Costco, which could be explained by the fact that large houses with large basements are usually needed to store products bought in bulk.

Companies in the grocery, household item and healthy/beauty realm could learn from such a category-intensive study, Seetharaman said. "This gives you a good sense of what you are winning, and how you are winning. But there's no silver bullet."

"Will it be a surprise?" Seetharaman asked. "Yes, it will be a surprise," he said. "The traditional wisdom is: Walmart is an aggressive, everyday-low-price price retailer and Target is the assortment retailer. So let's say both mass merchandisers … each of them has a certain strategic positioning and therefore thought they attract a certain type of consumer.

"We are upending that wisdom a little bit here: No matter what kind of strategic positioning you have carved out, consumers have a mind of their own. They are choosing to do different things in different categories. And businesses should wise up to this. Even your core customer is buying categories at other shops."