You're in Whole Foods, and even though you've gotten everything on your list, your boyfriend is loitering in the cereal aisle. As you linger, those chocolate covered acai blueberry candies catch your eye. Hm, those are a good snack--into the cart they go. While you're at it, might as well grab a pack of gum and a lint roller, I mean, they're just on display right there.

You've almost doubled the contents of your basket, and it's all thanks to the domino effect of impulse decisions.

Retailers use a myriad of tactics to entice shoppers to buy more. Upbeat music, fresh flowers, seasonal scents, buy-one-get-one deals, and even strategic clutter are all meant to create an atmosphere of blissful consumption. And many, especially grocery stores, employ the strategy of placing bread-and-butter items in the back of the store, forcing customers to spend more time and see more products, even if they only came for the basics. 

But a new study by the American Marketing Association, brings some nuance to the age-old strategy--that is, time is also a factor in how much people will spend. By polling 328 shoppers, researchers came to the conclusion that the more time one spends in a store the more he or she will buy. 

Researchers asked customers entering a store what they planned to purchase and their budgets, both overall and for planned purchases. Providing a handheld scanner, researchers asked shoppers to scan the bar code of each item they placed into their cart. As customers left the store, researchers examined their receipts to see what they purchased and the scanner data to see the order in which the items were chosen.

The study found that with every unplanned item a shopper choses, her propensity to make more unplanned purchases increased. This goes against intuitive thinking that a shopper may only allow herself one or two impulse buys before saying, "That's enough." In fact, for most customers, this trend continued even when they've exceeded their pre-determined budget.

Researchers also found shoppers used a licensing effect, wherein making a planned purchase gives the shopper permission to make an impulse buy, especially if they've already broken the seal with a previous unplanned selection.

So instead of relegating those items that may not be necessities on everyone's list to the checkout counter, intersperse them throughout the store. You'll increase the probability that a shopper will pick them up, leading to more and more unplanned decisions throughout the remainder of the shopping trip.