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

With the holidays now firmly in the rearview mirror, all focus this week for the broad-based S&P 500 (SNPINDEX:^GSPC) has been on a monster amount of economic data, and the start of earnings season.

On the economic data front, we received modestly positive news with regards to jobs, inflation, and the housing market.

Weekly initial jobless claims fell by less than 1% to a seasonally adjusted 326,000. This is a further sign that the jobs market appears to be stabilizing, with unemployment under 7% for the first time in six years.

With regard to inflation, the December Consumer Price Index rose 0.3%, right in line with expectations, while core CPI rose 0.1%. Neither figure is a huge surprise given the 0.4% increase in the Producer Price Index, meaning businesses are having little trouble passing along price increases to consumers at the moment. Rising prices are a good sign for a rebounding economy.

Finally, the National Association of Homebuilders Housing Market Index reading for January of 56 was a bit lower than expectations of 57, but still signals wide-ranging optimism throughout the sector that 2014 will prove to be another year of housing sector expansion.

What ultimately drove the S&P 500 lower on the day, then, you wonder? That would be a handful of disappointing earnings reports, including that of big-box retailer Best Buy (NYSE:BBY), which tumbled more than 30% at one point after revealing disappointing holiday-season sales. Same-store sales fell 0.8% during the all-important nine-week period, while domestic revenue declined by $160 million, to $9.75 billion. As a retail staple for the electronics sector, this could portend bad news for multiple electronics and retail companies when they report earnings this quarter.

By day's end, the S&P 500 had pushed lower by 2.49 points (-0.13%) to close at 1,845.89, ending a two-day push to new highs.

Leading all gainers to the upside today, and brushing off the earnings warning clouds, was clinical-stage biopharmaceutical company, Sarepta Therapeutics (NASDAQ:SRPT), which gained 40.1%. The huge advance comes on the heels of a presentation at the JPMorgan Healthcare Conference, and a press release that delivered updated clinical data from a phase 2b study of eteplirsen for Duchenne muscular dystrophy. According to the press release, patients demonstrated a continued stabilization of walking ability in the six-minute walk test at the 120-week mark, with a statistically significant treatment benefit of 64.9 meters over the placebo, and have experienced a decline of just 13.9 meters in walking distance, which is less than 5% from baseline. It's still worth noting that the Food and Drug Administration hasn't accepted increased dystrophin production as a viable endpoint yet, so Sarepta will have to still complete a larger late-stage study to demonstrate the effectiveness of its drug; but this is more evidence to back up the initial successes of its mid-stage study.

Media measurement and distribution company Rentrak (NASDAQ:RENT) galloped higher by 26.6% after it announced this morning that CBS had agreed to become its first major broadcast network to subscribe to its advanced demographics ratings service. Rentrack's demographic service provides networks with valuable viewer information that they can then pitch to advertisers, which leads to more focused advertising, and better ad rates for the network. While there's little denying that this is a big win for Rentrak, we're currently talking about a company whose shares are up about 140% since the early summer, and which still isn't profitable on an annual basis. Unless Rentrak lands significantly more high-profile customers, I'd call its current valuation a bit frothy, and worth avoiding until its bottom line catches up.

Finally, skipping from one Duchenne muscular dystrophy (DMD) rival to the next, Prosensa (NASDAQ:RNA) advanced 24.4% after also presenting at the JPMorgan Healthcare Conference, and issuing a press release outlining additional clinical studies of drisapersen, its DMD drug, which failed miserably in late-stage studies in September. According to Prosensa, after further review of its clinical studies, it believes that earlier treatment of the disease, and therefore a longer period of treatment, could delay disease progression. Furthermore, Prosensa intends to consult with clinical experts and regulators to determine the next move for drisapersen. As I stated earlier today, I wouldn't get too excited about these initial findings, with the experimental drug delivering such unimpressive results in its phase 3 study. In addition, Prosensa no longer has a partner -- GlaxoSmithKline ended  its pact with the company earlier this week. 

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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