The correlation between the stock market and the real economy

In his classic book "The Intelligent Investor," the great money manager Benjamin Graham wrote that "the investor with a portfolio of sound stocks should expect their prices to fluctuate and should neither be concerned by sizable declines nor become excited by sizable advances." If you can't exercise that kind of emotional control, then by Graham's definition you aren't an investor at all.

I recently came across yet another article expressing concerns that the stock market may be over valued at this point. It does point out that during a lot of economic recoveries, the stock market doesn't necessarily go the same way. Coincidently, I saw another article regarding how during some economic crisis, the stock market doesn't always collapse, which I'll have to try to find for this. This is another article that ties into this regarding how GDP growth and stock market returns don't correlate.

Apparently, it ain't so. There is no relationship between a country's high GDP growth and stock market returns, especially not in the long run and only weakly in the short run. In Economic Growth and Equity Returns from SSRN, professor Jay Ritter calculated that there was in fact a negative relationship between economic growth and stock returns in 16 major countries (including Canada and the USA) over the period 1900 to 2002 - this chart is taken from the paper.

Overall, I'm concerned that the stock market could go down further, however, I do feel that the economy is starting to turn around. At the same time though, I'm also expecting unemployment to trend higher for a little while longer. Question of the day though, do I get excited by sizable gains and concerned over significant declines? I get concerned any time anything looks irregular. Watching Al Gore's Inconvenient Truth gets me worried for the simple fact that if he isn't right the temperature isn't going to rise and disaster isn't upon us, correlation has broken down. There are unknowns challenging our understanding and I don't like that. After all, it's not what you don't know that screws you over, it's the things that you're certain of that are wrong that make you look nuts in the eyes of history.
With regards to current times though, I will be happy if cash flow is maintained and news releases don't cause me to wonder if declines are on the horizon. Though a significant decline right now would probably cause me to pause and re-evaluate my options and cause me a little bit of worry. Probably a healthy response.