How likely are online shoppers to walk away from a purchase? It depends on what step in the process they are asked, “How many of that item do you want to buy?”

Kristen Duke, an assistant professor of marketing at the Rotman School of Management, has discovered that customers are more likely to purchase an item when they are asked about the purchase quantity at the same time as when they click “add to cart.”

“It's surprising because it's such a simple thing,” says Duke. “It’s an opportunity for customers to recognize how their decision journey might be influenced without them even knowing it, and to think more intentionally about their purchases.”

Duke and her colleague On Amir at the University of California San Diego published their findings in the paper “The Importance of Selling Formats: When Integrating Purchase and Quantity Decisions Increases Sales.”

They found that customers are more likely to buy an item if they are thinking about how many they might want to buy at the same time that they think about whether they want to buy.

One way this happens is by baking quantities into the “add to cart” phase (for example “add 1 to cart,” “add 2 to cart,” “add 3 to cart,” etc.). This is referred to as the “quantity integration” format.

In contrast, the researchers found shoppers are less likely to make a purchase when prompted to think about purchasing but not quantities — presenting just an “add to cart” button, and letting customers decide on the quantity at a later step (such as once on the checkout screen). This method is known as the “quantity sequential” format.

Duke says the research is rooted in a decades-old marketing theory about the psychological decision-making process customers generally go through when making a purchase.

First, people identify whether they have a need for an item. Then they identify and compare different brands to determine which, if any, is most attractive. The final decision comes as they pull the trigger and buy or put the item back on the (virtual or real life) shelf.

Duke says when online stores use the quantity-sequential format (how many you want to purchase after you’ve added to cart), customers are more likely to ask themselves whether they need the item – placing them in the initial stage of the shopping process, which makes them less likely to make the purchase.

In effect, people faced with the choice to purchase without considering quantities tend to “dismiss the choice without thinking it through deeply” Duke says. They have broader dismissive thoughts like, “I don’t need chocolates right now,” and will ignore the great price, or will think “I don’t even like chocolate, so why would I buy Lindt?” Duke adds.

In comparison, the integrated model (how many do you want to add to your cart) helps customers skip to the later stages of the shopping process – giving them fewer reasons to say no, and making them more likely to follow through with the purchase.

In this format, Duke says participants also noted, for example, that they didn’t like chocolate, but saw the deal as an opportunity to buy the product as a gift.

“If you are asking yourself, ‘do I want to buy one bag of these particular chocolates, two bags or no bags?’ it compels to zoom in on that choice. You aren’t thinking as much about whether you’d like to purchase desserts in general. Instead, you’re evaluating if this specific brand of chocolates at this given price point is good value for you," Duke says. “Essentially integrated people think it through more.”

To test these ideas, Duke and her colleague conducted a field study with printer company HP, and 36 separate lab studies that included more than 20,000 participants.

Over a two-and-a-half-week period, HP customers were randomly assigned one of the selling formats - either quantity integration or sequential integration. The researchers found that businesses in the quantity integration group were nearly 12 per cent more likely to follow through on a purchase.

They found the same effect across all studies, regardless of products and price points: People were more likely to purchase an item if they were asked to indicate the quantity at the same time as adding to their cart.

Duke adds that the obvious takeaway for online stores is that integrated formats lead to higher purchasing, and therefore more revenue. But there’s also another takeaway: Online retailers might be able to curb unnecessary over-purchasing — and thus avoid costly returns or issues with low inventory — by switching to the sequential format.

“If people ask themselves if they really need an item right now, that might actually cue them to slow down their consumption,” she says.

That’s not to say quantity integration is bad for consumers, Duke adds. On one hand, being aware of this visual cue can help consumers more critically evaluate whether a purchase is worthwhile. But on the other hand, when faced with the quantity-sequential format (choosing how many you want to buy after it’s in your cart), people might talk themselves out of purchases, without really processing the details of the choice, Duke says. “And they may end up being worse off because they didn't buy something that could make their lives better.”