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Load an online shopping cart with gifts in the correct colors and sizes. Plug in the credit card number and shipping address. Then, watch in horror as the screen freezes, the browser crashes and the cart is empty once again.

The common holiday mishap now is under scientific scrutiny. It's the subject of Brigham Young University research pinpointing when and where online shoppers' blood begins to boil.

As Web users become more flustered or upset, their computer mouse flits about, and it takes longer to navigate a page, found the study published online this month in the academic journal MIS Quarterly.

The finding may seem common-sense, but it's big news for marketers and developers who hope to retain shoppers and viewers by building friendlier websites, said BYU information systems professor and co-author Jeff Jenkins.

Jenkins points to other research showing that flummoxed users spend only 10 seconds on an aggravating site before heading elsewhere.

Many existing programs tally page views and reveal where viewers stop scrolling. But this technology adds a more intuitive side to all that data.

To measure the effects of frustration, Jenkins and his colleagues in Germany and Hong Kong tracked about 500 participants who were customizing cars and computers on Dell and Volkswagen websites. They arranged for the screen to freeze, then sent an error message, and asked the participants to indicate their frustration levels on a scale.

Researchers also set BYU student participants up for failure, asking them to peruse accessories like purses before creating glitches.

Participants who reported being unnerved moved the mouse around 20 to 30 percent more. They also were distracted enough that their navigating took about 20 percent longer.

"It's not a silver bullet," Jenkins said, adding that the tracking system he developed is just over 80 percent accurate. "But it would give you an idea of what's working and what's not."

Jenkins has applied for a patent and runs a startup that will sell the technology. And the operation could expand. He believes he could study mobile devices in much the same way, analyzing finger swipes and taps.

Twitter: @anniebknox