Think back to December, when you were in the thick of your Christmas shopping. How did you pick out that perfect scarf you put under the Christmas tree for your sister? How did you know you got a good price on those Beats by Dre headphones for your nephew?

If you're like most shoppers, the answer is likely that you did plenty of research before opening your wallet.

The Web has made it easier than ever for consumers to make price comparisons and to access product reviews, and that has meant that today's shoppers are frequently armed with reams of research by the time they pull the trigger on a purchase. And they're not making impulse buys like they were in the days before the recession.

This dynamic is creating major challenges for retailers, who must now figure out how to thrive in an era when the consumer is ultra-knowledgeable - in many cases, more knowledgeable than the store's own sales staff.

A new study of U.S. consumers, conducted by professional services firm PricewaterhouseCoopers, shows just how prolific this shopping behavior is becoming.

In its annual shopping survey, PwC asked shoppers how likely they are to conduct research before making specific types of purchases, including everything from jewelry to toys to clothes. The share of shoppers who did not conduct research was already fairly small in every category back in 2013. But more striking is how much the figure decreased in every category in 2014. In each case, significantly fewer shoppers are not researching before they buy.

This may not seem especially surprising if you remember the "showrooming" panic that became a fixation for brick-and-mortar retailers several years ago. Back then, they were worried that shoppers were coming into their stores to try on or test out merchandise, only to go home and purchase them online from Amazon.com or another e-commerce competitor.

But that perceived threat hasn't quite materialized the way many retailers expected. In fact, the PwC survey, along with many other recent research studies, suggests that "showrooming" is far less common than its opposite, a practice the industry has dubbed "Webrooming," in which people browse online before ultimately going to a store to make a purchase.

So here is the gauntlet that consumers have thrown down for retailers: They continue to want to shop in physical stores in large numbers_for now,only about 7 percent of purchases in the U.S. are made online.

But by the time they get to the store, shoppers already know exactly what they want, and they want to get in and out of the store quickly. And this attitude makes it extremely hard for retailers to upsell them on a fancier kitchen mixer or persuade them of the merits of buying a protective case for their smartphone. And it makes it hard for them to provide outstanding customer service, since store clerks now have to assist shoppers who might already be experts on what they're buying.

The silver lining in this data for traditional retailers is that it makes clear that stores are hardly becoming an obsolete part of the shopping process.