Amazon rarely releases sales data to the media. Nonetheless, the idea that customers who subscribe to Amazon Prime wind up shopping and spending a lot more at Amazon is considered fact. After all, once customers are paying $99 for the service and know that express two-day shipping is available for free on nearly all purchases, it makes sense that they’ll stop shopping elsewhere and do most if not all of their online shopping at the site. It helps, of course, that Amazon has a reputation not only for selling a huge variety of merchandise, but for having low prices as well. But what impact, exactly, does signing up an Amazon Prime membership have on the individual’s online purchasing habits? Again, it’s hard to say because Amazon is reticent to release data. What’s more, things are complicated because the people who find it most worthwhile to join Amazon Prime are those who shop often at Amazon in the first place. (When you’re a member, the more you spend, the more you “save,” at least in terms of shipping.) So it’s not simply a matter of figuring out how much Prime members versus non-Prime members spend at the site. Still, it’s undeniable that Prime members spend a bunch more at Amazon than non-Prime members. In a recent story by a couple of my MONEY colleagues about Apple, Amazon, and Google in terms of investing opportunities, a ComScore report is mentioned revealing that “Prime members make twice as many purchases as nonmembers, and they spend 40% more per transaction.” Read more: Why You Should Never Buy Stuff When You’re Sad This week, a new survey was released by Consumer Intelligence Research Partners (hat tip: Huffington Post) with some precise dollar figures regarding the topic. According to a survey of consumers who made purchases at Amazon from October to December 2014, Prime members say they spend an average of about $1,500 at the site annually, versus $625 for non-members. Owning an Amazon Kindle is also correlated with increased Amazon.com spending. Kindle owners (who may or may not also be Prime members) spend $1,450 per year at Amazon, compared to $725 per year for customers who don’t own Kindles, according to the survey. “Similar to Amazon Prime members, Amazon Kindle owners are better customers,” Mike Levin, partner and co-founder of CIRP, said in a press release about the new report. “They also shop more frequently, and also buy more expensive items on average.” All in all, the spending data spells out plainly why Amazon pushes sales of Prime and Kindles so hard. In particular, the world’s largest retailer has been relentless in upping the Prime value pitch by adding streaming services, producing original movies, and such. Just last weekend, for instance, Amazon dropped the price of Prime to $72 and allowed everyone to stream its Golden Globe Award-winning online show “Transparent” as a way to show off one of the perks of being a Prime member. Read more: Amazon Is Making It Easier to Publish Your Own Kindle Textbooks It’s no mystery that Prime membership, Kindle ownership, or both are essentially gateways that welcome online shoppers into the Amazon consumershere and result in sharply increased spending at the site. On the other hand, there’s good reason to believe that people who aren’t Prime members are more likely to shop around and make purchases at Amazon only when it’s clearly the most convenient or cheapest option. They don’t automatically defer to making purchases at Amazon, like Prime members appear to do. And based on some recent studies indicating that Amazon doesn’t have the cheapest prices across the board, it seems wise to browse a range of retailers rather than immediately head to Amazon for a one-click purchase of your latest need. Read next: Amazon Outbid Netflix For Its Most Successful Show Sign up for THE BRIEF and more view example Listen to the most important stories of the day.