The “style is dead” meme has been around for a decade, Dave, and it’s been wrong the whole time.

Your recent blog presents the same tired argument: Growth and value show high correlations to one another. Therefore, why bother using them in a portfolio?

I’ll tell you why: Because they work.

People who argue differently have their heads stuck in the ivory tower, too worried about “correlation quotients” to think about what actually matters to investors, which is returns.

Let’s take a simple case. Since the market bottomed on March 9, the rolling three-month correlation between the iShares Russell 3000 Growth ETF (NYSEArca: IWZ) and the iShares Russell 3000 Value ETF (NYSEArca: IWW) has been well over 0.90. To academics, the two are essentially identical.

But in the real world, there’s been a huge difference: IWV has outperformed IWW by more than 7 percent, in a period of just 6 six months. It has also beaten the broad market iShares Russell 3000 ETF (NYSE Arca: IWV) by 3 percent.

Now consider a different stretch: from Sept. 15, 2008 (the day Lehman Brothers went bankrupt) through March 9, 2009. The correlation between IWW and IWV over that stretch was again consistently above 0.90, but on a performance basis, IWW outperformed IWV by 10 percent.

What happened is obvious: After Lehman’s bankruptcy, the market started punishing risk. Not surprisingly, growth stocks (which have stronger fundamentals than value stocks) outperformed. When the market bottomed, investors started to reward risk again, and value gained.

An investor who timed that transition perfectly … who bought growth on Sept. 15 and switched into value on March 9 … is now 8 percent ahead of an investor who just bought the market and held on.

I’m not saying it was easy (or even possible) to call that transition perfectly. But even if you missed it by a week or a month, you still did well.

Not everyone has the inclination or temperament to tweak the risk focus in their portfolios on a real-time basis. I don’t. But I know some investors and advisers that do, including some who have been doing it successfully of late. For them, growth and value (like large-caps and small-caps) are useful.