The day after Thanksgiving kicks off the holiday season in a bacchanal of bargains and deals. But many of these purchasers aren't made for the person buying; they're gifts. Research shows that the distinction matters for how people spend.

About a quarter of adults are "tightwads" and another quarter "spendthrifts," said Scott Rick, a marketing professor at the University of Michigan. Spendthrifts are people who spend too much money and are unhappy about it. Tightwads spend too little and want to indulge more, but find parting with cash painful.

Normally, the difference in spending between the two groups is significant. But Rick has found that when the holidays roll around, the gap shrinks. Gift-giving doesn't follow the regular rules.

There are a couple reasons that the holidays might pry open the pockets of even miserly types, Rick said. First, the joy of gift-giving could outweigh the pain of spending. Second, buying gifts is not really a choice, at least if you want Grandma to continue speaking to you.

"You have to have something under the tree for this list of people," Rick told LiveScience. "So if you're a tightwad, you might still have the normal level of pain, but it doesn't matter. It's not optional."

Rick doesn't know whether spendthrifts or tightwads are more drawn by holiday sales, but suspects that the holiday season drags more of the latter to the mall.

On Black Friday, he said, "because of the compulsory aspect, I think you'll see a lot more than usual."

You can follow LiveScience Senior Writer Stephanie Pappas on Twitter @sipappas.