And this one gets better. If you manage to find the previous year’s model online, you can take off another 19.36 percent ($14.50), on average, the data show.

“For most runners, they know what shoes work for them, and for them, saving 38 percent on average, it makes sense to buy it online,” said Jens Jakob Andersen, founder of the website, which bills itself as the Yelp of running shoes. “I was surprised to see the number was this big.”

The independent running shoe website looked at 183,911 online purchases of running shoes on March 1, 3 and 6 and compared them with manufacturers’ suggested retail prices in bricks-and-mortar running-shoe stores. More than 2,400 shoes across 36 brands — more than 99 percent of the market — were covered in the survey.

It turns out that 86 percent of all running shoes are available at a discount online, including top brands such as Nike, Brooks, Asics and Adidas, all of which can be found at 31 percent to 40 percent off.

The top savings were on Scott (62 percent), Reebok (53 percent) and Skechers (53 percent). Vibram FiveFingers and Topo Athletic shoes were at the bottom, with 15 percent off — still not too bad. When it comes to which online retailer provided the best discounts, Sierra Trading Post, at 41 percent, was tops, while RoadRunner Sports lagged the field at just 1 percent. (Amazon, whose founder, Jeff Bezos, also owns The Washington Post, took silver with the second-best prices and gold for widest selection.)

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So what’s going on here, besides the obvious theory that online retailers don't have the overhead costs of traditional stores? Andersen believes that the Internet enforces a price transparency that you can’t find at stores. Few people will take the time to price a pair of shoes at 10 different stores, so manufacturers can control prices in those facilities by acting as a sort of cartel. All the brands in a given store are marked up into much the same range, he said. But checking a dozen prices online requires only a few clicks, so competition is real and fierce.

“They are dictating this market,” Andersen said of the big footwear manufacturers. “But on the Internet, it is so hard for them to dictate it.”

I contacted representatives for Nike and Brooks, who are familiar with Andersen’s previous surveys, to see what they thought of this one, but I did not hear back with answers to my questions as of Wednesday. If either gets back to me, I'll update this post.

Tony Post, founder and chief executive officer of Topo Athletic, said in an email that “we try to manage our brand in support of the consumer and the local retailers. We sell to a few online dealers, but we still think the best place to test [and] experience the brand is in a specialty store — alongside 4 or 5 competitors.

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“We price our products modestly from the start, so consumers get a good value and our retailers don’t have to discount in order to drive sales. We manage our own cost structure to deliver value that works for the consumer, the store, the factory, and Topo.”

Robyn Gault, owner of Fleet Feet Sports, a running store in Gaithersburg, Md., said that unlike online merchants, small running stores are part of their community and serve them in numerous ways — by employing local people, paying taxes, hosting fundraisers, sponsoring running events and offering expertise.

If online dealers kill local businesses, “next time [people] want to try [shoes] on and take an hour of a staff’s time and then buy them online, they won’t have a place to go,” she said in an email.

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Andersen, a Dane who lives in Norway, founded the website to offer objective information on running shoes and running to help more people enjoy the sport. He accepts no ads but now is taking a commission from companies for sales made through his site.

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He acknowledged that one of the big drawbacks of shopping online is that you might sacrifice fit and comfort, which can’t be overstated when it comes to running gear because you can’t try on the shoes. You can send them back, of course, but how many times do you want to do that?

Andersen said that online three-dimensional scanning technology available through websites such as Shoefitr.com is making strides toward solving that problem. And if your conscience allows it, you can always try on a bunch of shoes at the store until you find one you like, then go home and buy them online. (I'm not sure I’d pull that at the same store more than a few times, but that’s between you and the store.)

Some other nuggets unearthed by Andersen's research:

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• Racing shoes are about 17 percent cheaper than everyday training shoes.

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• In general, the worst-reviewed shoes offer the highest discounts. So keep those reviews coming, and be honest.

• The more arch support you need, the more you'll pay.

• Heavier shoes are more expensive, by about $5.60 an ounce. But because the survey mixed racing shoes with everyday trainers, it’s difficult to draw a conclusion from this information, Andersen said.