They say that figures never lie. But in a world where body image is a numbers game, vanity sizing is like skinny mirrors: rampant, warped and, more often than not, welcomed by shoppers. In the fast fashion realm, it’s not abnormal to drop a dress size without losing a pound. With major brands pushing their ready-to-wear sizes below zero and consumers turning to the convenience of online shopping, the topic is more relevant than ever.

“There’s been a huge change in sizing. I always say one of the largest retailers, Banana Republic, has been the most apparent,” says Toronto-based fashion stylist Rachel Matthews Burton. “Banana Republic is a benchmark for other retailers. I own a tuxedo jacket from there that is probably 12 years old and it’s a size six. If I was to go and shop for that jacket right now, it’s likely it would be a size four or smaller.”

Rachel Matthews Burton: “There’s been a huge change in sizing.”

Sizing irregularities have existed for many years and are most common in Canada, the U.S. and the U.K. According to a New York Times article on the subject, a woman with a 32-inch bust would have worn a size 14 in 1937. In 1967, the same woman would have worn a size eight. Today, she would be considered a size zero.

The phenomenon has long been speculated to be a marketing ploy to appeal to body image-conscious shoppers, and recent research shows that it’s working.

One study published in the October 2012 issue of the Journal of Consumer Psychology found that American women experienced a self-esteem boost when they thought they were able to fit into a smaller size.

A look at the many sizing chart variations raises the question of whether inflated egos are really worth the inconvenience.

“As a stylist, it means you have to keep up with different retailers’ sizing,” says Burton. “North American women are often bigger than European women and, therefore, North American clothing manufacturers cut to larger sizes. A size two in Zara is drastically different than a size two in Banana Republic.”

Europe’s slimmer fits have not gone unnoticed by North American shoppers. Elle Magazine even addressed “Zara’s sizing problem” by asking readers if the Spanish brand should adjust their sizing to match the roomier fits that Americans are accustomed to. The Economist also cited Zara’s slim-fit clothing as one reason why the brand isn’t more popular in the U.S.

Angie Sakla-Seymour says that vanity sizing has led to increased shopping among women.

“Women who used to wear a size 12 now believe they’re a size 10. It makes them feel good,” says Angie Sakla-Seymour, owner of Angie’s Models and Talent Agency.

“It also makes women shop more. If you can fit into smaller sizes, you’re more inclined to go ‘therapy shopping.’”

While there’s no doubt that size inflation can offer a self-esteem boost, others have argued that sizing changes are not for vanity’s sake, but necessary to fit the growing girth of the average customer, depending on nationality. As humans evolve, they get bigger, not smaller, and the practicalities of sizing must accommodate this growth, says Burton.

Canadian designer Christopher Bates confirms that vanity sizing is common in menswear as well.

Men’s apparel is affected too. Just ask menswear designer Christopher Bates, who says he follows the industry standard of vanity-sizing his pants by two inches, and offering slim and relaxed fits in order to accommodate a broad client base.

“The waist measurement in men’s pants is always vanity-sized. Typically by two to three inches, which is a lot. I don’t foresee this changing in menswear,” he says.

While global standardization is impractical due to region-specific size variations, shopping for womenswear now involves knowing your measurements and knowing your brands.

“I personally will never shop for pants online because I am notoriously difficult to fit for pants,” says Burton. “Size means nothing when you’re shopping online. You go straight to the sizing charts and you have to know your measurements. It’s just a number.”

It may be just a number, but it can mean all the difference to some shoppers. With e-commerce on the rise, brands will be forced to address how vanity sizing affects online sales, returns and, ultimately, their bottom line.