Some experts say we're already in recession

More than a dozen key measures of economic strength have peaked this year, suggesting we may be in a recession despite annualized gross-domestic-product growth of 3.9 percent in the third quarter.

"We may already be at an inflection point," says David Rosenberg, U.S. economist for Merrill Lynch. "A lot of things that usually peak before the turn of the business cycle have already peaked."

Rosenberg is advising clients to increase their exposure to highly rated bonds and avoid stocks in economically sensitive sectors such as automotives or retailing.

"Every part of the business cycle has a particular investment recommendation, and this one would be to get defensive and focus on quality."

Recessions are tricky to predict. The 2001 recession wasn't "officially" announced until 2003 by the National Bureau of Economic Research.

Most recessions are marked by two consecutive quarters of declining economic growth. The bureau looks for diminishing activity in income, employment, production and wholesale and retail sales.