This Big Idea in Women's Fitness Wear Created Millions of Loyal Shoppers A clever approach to customer acquisition and retention helped one ecommerce company create an army of passionate customers.

How do you get customers not just making one purchase, but coming back to your site, again and again every month? It's something that haunts and stumps countless entrepreneurs. One company has nailed it, having developed a system that not only addresses this problem but also offers a huge service to their customers.

Say hello to Fabletics, the fitness-wear company founded by actress Kate Hudson, along with Don Ressler and Adam Goldenberg – founders of TechStyle Fashion Group, owners of leading fashion-subscription ecommerce site and lifestyle fashion brand JustFab. Motivated to support women to lead healthy and active lives, Hudson – best known for her roles in movies such as Almost Famous and How to Lose a Guy in 10 Days – started Fabletics in Fall 2013.

Right from the start, the ecommerce company instituted a clever way to get site visitors coming back over and over: a quiz. Here's how it works.

A customer will land on the site and be led through a series of simple questions about their exercise habits and style preferences, among other topics. After that, they are directed to a page full of outfits chosen specifically for them, based on their responses.

It takes people only about a minute to fill out the quiz, on average.

From there, customers can choose to shop as a visitor, purchasing products at retail price. Or they can opt in to Fabletics' Flexible VIP Membership program, where they receive 50 percent off their first outfit and a discounted price (up to 50 percent off retail prices) on all other items purchased.

t's like virtually walking into your favorite store and always getting up to 50 percent off.

Each month, Fabletics offers a new collection of signature styles and patterns for all customers. Meanwhile, VIPs have the option to shop the collection or skip the month for no charge – otherwise VIPs will be charged $49.95 that will go to a credit that they can use for future purchases.

So far, it appears the quiz is working. Of the more than 53 million people who have started the quiz, some 34 million have completed it.

"Our members absolutely love it," says co-founder Adam Goldenberg. "We now have more than 1 million VIPs in less than three years. Members are visiting their boutique 20 to 25 times per year and buying about four times per year on average."

Last year, the company even began opening brick-and-mortar stores around the U.S.

Turns out, the data Fabletics collects about customer preferences via its quiz, and the commitment from members to visit the site at least once per month, provides at least two significant business advantages:

• Fabletics has very low inventory waste because they're creating clothing they know their customers want (calculating style preferences and predicting production needs at 95 percent accuracy, the company says).

• No need to spend marketing dollars re-acquiring customers.

These two factors reduce its overhead by 30 percent to 50 percent, compared with standard retail. Fabletics says it passes back to customers in its VIP pricing. "This relationship is a big part of our success," Goldenberg says. "It allows customers to get lululemon quality at a fraction of the cost."

In all, Fabletics says it has shipped more than 4.5 million orders since the company launched just three years ago. Who knew a simple online quiz could pack such a powerful business punch?