Nouriel Roubini, the once obscure New York University economics professor who two years ago predicted the current global financial crisis and recession, said those who are turning bullish on the U.S. stock market need to reassess the data.

Roubini told Bloomberg News he was "still quite bearish on U.S. and global equities." Despite losing much of their value already, Roubini thinks they could still lose another 15-20% before any recovery beginning towards the end of 2009.

Caveat emptor: let the (stock) buyer beware

The S&P 500 has fallen more than 40% in 2008, and with a forward P/E of about 12, one could make the case that stocks are at least approaching cheap levels, based on the post-World War II P/E average of about 17. Economist Richard Felson is not of that camp.

"Cheap compared to what? Compared to bull market high P/Es of 25 or 26, yes, but that assumes a) a return to GDP growth levels experienced before the recession hit; and b) that stocks won't drop to lower levels. You can't assume either, so Roubini's downside forecast may represent 'discretion being the better part of valor'," Felson said. "This is a risky time to own stocks or increase positions. Stocks could become much cheaper, particularly if the recession lasts into Q3 2009."

One hears the mantra almost daily, often from friends and relatives:

Aren't stocks cheap? Look at those low P/Es! GE is at $15 a share, Intel below $14, Du Pont at about $27. My goodness, the Dow is down to 8,200. Isn't now a good time to buy stocks?

It is, if you believe the Dow is forming a bottom and/or that the worst of the financial crisis is behind us, and the U.S. economy is set to recover.

However, the alternate viewpoint argues that the Dow has not bottomed, could very well fall another 1,000 points, with panic selling (known as 'capitulation' in Wall Street circles) taking the Dow to levels well below that, at least for a short period of time, possibly longer.

Hence, purchasing shares for the first time now (or adding to existing positions) given the latter scenario would create an immediate 10% loss, or possibly more.

Monitor corporate earnings and job growth

What's a better tack to take concerning when to buy more shares? Monitor U.S. corporate earnings and job growth.

Investors have become accustomed to bull markets -- long periods of stock price appreciation, i.e. a rising stock market. That's been the norm since the start of publicly-traded stocks in the United States, and certainly a feature of markets in the post-1980 period.

Provided that the U.S. economy is growing in a sustainable way and increasing its productive capacity, bear markets have been the exception, the momentary pull-back, when one takes a long view of the investment horizon.

The current bear market can be seen in that light, again, provided the nation's economy is on a sustainable growth track with an increasing productive capacity.

Still, the key in the above has been the U.S. economy (obviously). Absent a healthy economy, different Dow case studies pop up.

For example, what if the Dow didn't fall -- and didn't rise -- for seven years? In other words, a sideways Dow where no progress is made? It seems like a remote possibility, but that's exactly what occurred from early 1966, when the Dow fell below 1,000, until late 1972, when the Dow reclaimed the psychologically-significant 1,000 level.

Is it time to rein-in expectations regarding the Dow?

Indeed it is, if technical analysis and historical p/e ratios mean anything.

Those with visions of a Dow of 11,000 dancing inside their heads need to take a step back, for context and perspective, on the likelihood of a Dow push to that level in the near future.

The U.S. economy is in recession, it's shedding jobs, downward corporate earnings revisions are likely, and the world's major economic regions are attempting to re-liquefy credit markets and prevent a global financial crisis from further damaging economies, worldwide.

The above, as CNN Talk Show Host Larry King would say, 'ain't exactly signs of prosperity.'

And the Dow has responded: down more than 30% since hitting its all-time high above 14,000 a year ago.

Keep your eye on 8,500 / 8,200 / 8,000

Earlier in this space yours truly noted that the Dow had technical support at the 8,500 to 8,200 levels, and of course psychological support at 8,000.