There's an old saying: If it walks like a duck and quacks like a duck, guess what, it's a duck! Somehow, this common-sense rule is simply not applied to recessions.

Over the past few weeks, I've heard numerous money managers, or should I say "stock promoters," claims that the U.S. economy is not in a recession, and that they expect the economy to continue to expand during the months ahead on the resiliency of the U.S. consumer and on strong export growth.

These same money managers fail to acknowledge that the National Bureau of Economic Research (NBER) — the non-profit institution that determines the beginning and ending dates of recessions — historically has been unable to determine exactly when a given recession began until approximately nine months after the beginning of an economic slowdown.

The NBER defines a recession as a significant decline in economic activity, lasting more than a few months, that is normally visible in a country's inflation-adjusted production of goods and services, real gross domestic product (GDP), inflation-adjusted income, employment, industrial production, and both wholesale and retail sales.

According to the NBER, a recession begins just after an economy reaches a peak of activity and ends as the economy reaches its trough.

In contrast, many money managers, journalists, and other financial commentators typically define a recession as two consecutive quarters of a sequential quarterly decline in real GDP. That's a very important distinction, because the last time that U.S. GDP fell for two consecutive quarters was March 1991.

Therefore, if the NBER defined a recession in the same way as most journalists and financial commentators do, there hasn't been a recession in the U.S. since 1991. Try telling that to the thousands of U.S. consumers and businesses that experienced the brutal 2001 recession!

The fact of the matter is that the U.S. economy might already be in a recession: The rate of increase in real personal income fell for seven months in a row until the government provided U.S. citizens with a tax rebate; the employment situation has gotten worse every month this year, with the non-farm sector experiencing 463,000 job losses over the past seven months; and inflation-adjusted retail sales have declined (on a year-over-year basis) during every month since December 2007.

Meanwhile, the rate of growth in U.S. industrial production fell sharply between January and May of this year, and the total production of industrial goods actually declined during July.

In addition to the negative economic developments mentioned above, household net worth fell during each of the past two quarters; first-time claims for unemployment benefits rose last week to the highest level since May 2003; and the average consumer's debt rose during June to approximately 24 percent of their after-tax income.

Meanwhile, economic growth in Europe and Asia has slowed considerably over the past seven months, and the exchange-value of the U.S. dollar has rallied sharply against most other foreign currencies since mid-July.

Yet, the Wall Street cheerleaders have continued to try to convince investors that the U.S. economy will grow at a faster pace later this year because they expect consumers to continue to spend on unnecessary (that is, discretionary) items and for U.S. exports to continue to compensate for the ongoing slump in the housing market.

Very interestingly, an increasing number of those same "experts" have rotated a significant percentage of their funds under management to so-called "defensive" sectors of the market such as the consumer staples and healthcare sectors over the past three months. Should we therefore assume that those money managers have been purposely misleading investors, or is it just that they don't know what they are doing?

One thing is certain: If you listen to those folks, you'll probably have a tough time growing the value of your assets. Approximately 85 percent of mutual fund portfolio managers underperform a broadly diversified portfolio of equity securities, such as the S&P 500 Index, during any given year.

So, what should investors do? My experience suggests that most investors are better off following their own instincts and doing their own investment research. If, however, you're one of those investors who is either unwilling to do a lot of homework or feels that you don't have the right skill set to self-manage your portfolio, you may want to try reading my investment newsletter, The ETF Strategist.

My conservative investment recommendations have returned 4.4 percent since the inception of The ETF Strategist last September, while my aggressive recommendations have returned 13.5 percent.

In comparison, the S&P 500 Index has returned negative 10.8 percent (as of Aug. 15, 2008). Click here for a trial subscription to The ETF Strategist.