Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

It was a sea of red on Wall Street today, as the markets continue January's sell-off during the first trading day of February. The Dow Jones Industrial Average (^DJI 0.34%) ended the day down 326 points, or 2.08%, while the S&P 500 fell 2.28%, and the Nasdaq slid 2.61%. The big declines came after the Institute for Supply Management released data indicating that the Purchasing Managers Index, essentially an indication of how purchasing managers feel about the economy, fell from a 56.5 in December to 51.3 January. Analysts expected  a figure of around 56 for January.

Is it time to run for the hills and get out before things get worse? Well, we at the Fool believe in long-term investing, and I'm here to say that now is the time to do nothing, just as if the markets were up, rather than down, by 7% year to date. In fact, if you must make a move, buy more of the companies you love. There's no need to sell. For more about the market sell-off, read a few of my more recent articles about how to think about what's happening in the markets right now: "The Challenge of Fighting Your Emotions" and "How to Think About 2014."

Now, back to day's moves.

Pfizer (PFE -0.97%) was the only one of the Dow's 30 components that ended the session in the black. The stock rose 0.66% after the company announced that its breast cancer treatment palbociclib in clinical trials has successfully met its goals of delaying progressive symptoms in women who have locally advanced or newly diagnosed metastatic cancer. Some analysts believe this drug could top $5 billion in sales if the FDA approves it. If that happens, it could become Pfizer's next blockbuster drug.  

Two other winners may simply have had great days because of their Super Bowl ads. Shares of RadioShack increased more than 3.3% today, while CarMax (KMX -0.22%) saw a 1.44% rise. Neither company had any real news pertaining to it today, so it looks as if shelling out millions for a Super Bowl spot paid off, at least temporarily, for these companies.

Elsewhere, Apple (AAPL 0.02%) rose 0.19% as some analysts are now calling the stock a correction protection trade. Shares are currently trading at 12 times past earnings and under 11 times future expected earnings. The stock pays a 2.4% dividend yield, and while the company is set for a $100 billion buyback, many investors, including Carl Ichan are pushing for even more. The buyback plan alone should act like a backstop for shares to fall dramatically lower, which may be one reason the stock rose today, as many on Wall Street think a more substantial correction of 10% or more is on its way.