In the pre-digital era, people shopped for groceries by making a list of things they needed before heading out to a supermarket or other store to purchase them. Perhaps they were influenced by newspaper circulars, television ads, or even direct mailings, but most decisions were based on need as well as what was on store shelves. That's why the way items are placed in a grocery store is a science, and it's why brands pay for displays, prime locations, and other highly visible real estate.

Those things still have their place, but more than half (51%) of grocery purchases are digitally influenced, according to a new report from Deloitte. It's not that most consumers are buying their groceries online, it's that their buying choices have been made before they leave the house based on what they see online.

A shopping cart in a grocery store.

People's grocery choices are influenced by what they do online. Image source: Getty Images.

Online influences

"The majority of food and beverage purchases still happen in the store, but consumers' online or mobile experiences impact those purchases much earlier in the shopping journey," said Deloitte Vice Chairman Barb Renner in a press release.

Digital influence has slowly been rising across all retail categories, according to Deloitte. In 2013, only 14% of all retail transactions were influenced by what the consumer had seen online. That number has more than tripled to 56% across all categories with apparel (56%), home (58%), auto (59%), and electronics (69%) leading the way. 

The influence of digital makes more sense in those categories because they lend themselves well to online research. The fact that groceries have started catching up -- digital nearly doubled its influence year over year -- suggests that consumers are turning to their devices for help for all purchases.

"In our research, people saw room for improvement from grocers compared to digital experiences they find in other retail categories," said Renner. "Consumer products companies and retailers who create those digital touch points have a much better shot at getting the shopper's attention and loyalty before competitors, many of whom aren't even in the game yet."

What does this mean for grocers?

The increasing influence of digital makes data king for grocery chains. That may give an advantage to Amazon, which knows a lot about its customers. That becomes especially important when shoppers aren't looking up specific products.

For example, 77% of people use recipe websites and blogs to "drive awareness and find inspiration," according to Deloitte. That means that a company like Amazon -- that knows not just what you buy but also what people like you buy -- can find ways to deliver its customers the recipes that inspire them to buy certain products.

In addition, 80% of respondents "have used a digital device to browse or research grocery products, tapping sources like manufacturer and grocery retailer websites," according to the report. That should allow any data-smart retailer to stock its stores with the items consumers want, putting them in locations where they will be found.

The science of merchandising a store changes when more than half of shopping decisions are made outside the physical retailer. Amazon already has a patent for technology that allows it to ship an order before a consumer has actually ordered it. It also uses predictive technology to stock its warehouses and to pre-pack items for delivery.

It's not hard to see the company expanding its technical reach into grocery recommendations, sharing recipes, and driving sales at its Whole Foods chain. Wal-Mart may not have quite the same level of predictive data, but it can likely do some of the same as well.

What has become clear from this data is that if stores want to have a say in what people buy, they need to think beyond their brick-and-mortar in-store presentation. That's not going to be easy, or even possible, for every chain, but for the big boys, it's likely going to help the rich get richer.