For the second week in a row, investors, traders, and speculators had a holiday-shortened four-day week to buy and sell stocks. Having one less day usually doesn't slow the markets down, though, and that was certainly the case this week, as the Dow Jones Industrial Average (DJINDICES:^DJI) posted a weekly gain of 3.84%, while the S&P 500 (SNPINDEX:^GSPC) moved higher by 4.56%, or 64 points. The Nasdaq (NASDAQINDEX:^IXIC) performed the best, as it gained 146 points, or 4.94%, during the first few trading days of 2013.

Two weeks ago, the Dow's 30 components ended the week miserably, as 28 of them traded lower for the week. This four-day trading period was much better for the markets, as only one Dow stock ended the week lower.

The key driving factor for the markets this week was clearly the compromise in Washington that prevented the U.S. from falling off the peak of the fiscal cliff. With the politicians in D.C. agreeing to keep tax rates lower on the majority of citizens, the U.S. was saved from another possible recession, as many economists were predicting would happen if taxes on all Americans rose with the new year. On Wednesday alone, the Dow reacted by surging higher by more than 300 points.

But before I get to the Dow loser, I'd like to point out the big winner of the week. Although the stock was the worst Dow performer of 2012, Hewlett-Packard (NYSE:HPQ) managed to become the best stock to own during at least the first week of 2013. With the majority of the Dow technology stocks posting just modest gains of 2% to 3%, Hewlett-Packard posted an astounding 10.91% increase over just the past four trading days. While I don't believe this move higher is a sign of things to come, I also think there is too much risk involved in shorting the struggling personal-computer company at this time.

Other big winners this week were Caterpillar (NYSE:CAT) and Alcoa (NYSE:AA), which saw their shares rise an impressive 9.34% and 8.68%, respectively. Both companies are closely tied to the health of the economy and saw their shares depressed as investors waited to see what was going to happen in Washington.

Now to this week's lonesome loser
Last week, shares of UnitedHealth (NYSE:UNH) dropped by 1.71% as the majority of the Dow's 30 components fell into the red. But this week, UnitedHealth fell by 2.87%, and it was the only Dow component that ended the week lower. On Thursday, the stock lost 4.7% of its value after analysts at Deutsche Bank downgraded both UnitedHealth and its competitor WellPoint (NYSE:ANTM). Both stocks dropped from "buy" recommendations to "hold" as the analyst sees profits and margins coming under fire in 2013. The reason cited for the downgrade was a belief that medical costs will rise over the coming year while premiums won't.

Matt Thalman has no position in any stocks mentioned. Follow Matt on Twitter, @mthalman5513. The Motley Fool recommends UnitedHealth Group and WellPoint and owns shares of WellPoint,. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.