The S&P 500 index is a collection of 500 large-cap companies that represent "leading companies in leading industries." The index is oftentimes a benchmark of the overall U.S. stock market and is also part of many investors' portfolios through index funds and SPDRs. While the S&P 500 index lost 7.5% in the month of November, its bottom 10 companies have seen their stock prices fall even further.

Of course, a stock's price can drop for reasons both significant (e.g., the emergence of a powerful competitor) and insignificant (e.g., tax selling). Hence, a large drop in stock price could offer a unique buying opportunity, but it could also present a value trap.

That's why we've paired the 10 biggest S&P 500 losers for the month of November with the intelligence of our 120,000-member-strong Motley Fool CAPS community. Each company's CAPS rating should offer some insight into how our community views the company. As always, though, you should conduct your own fundamental research.

For the month of November, here are the S&P 500's 10 biggest market losers:

Company

Return in October

Year-to-Date Return

CAPS Rating (out of 5)

Additional CAPS Research

1. ProLogis (NYSE:PLD)

(72.6%)

(94.0%)

***

PLD

2. Tenet Healthcare (NYSE:THC)

(72.4%)

(76.2%)

**

THC

3. Genworth Financial (NYSE:GNW)

(70.0%)

(94.3%)

***

GNW

4. American Capital (NASDAQ:ACAS)

(69.8%)

(87.1%)

****

ACAS

5. Developers Diversified Realty

(63.6%)

(87.5%)

*

DDR

6. Jones Apparel Group

(53.8%)

(67.9%)

**

JNY

7. JDS Uniphase

(50.2%)

(79.5%)

***

JDSU

8. XL Capital (NASDAQ:XL)

(48.1%)

(90.0%)

*

XL

9. Office Depot (NYSE:ODP)

(45.3%)

(85.8%)

***

ODP

10. AK Steel Holding (NYSE:AKS)

(43.4%)

(83.0%)

***

AKS

Source: Capital IQ and Motley Fool CAPS. 

Join us on CAPS to further your research into these companies. Or check out the 10 biggest Dow losers for November.

The Fool has a disclosure policy, and it's not a loser at all. American Capital is an Income Investor recommendation.