Life for chief financial officers is getting tougher with a new study, to be released next month, showing that roughly half of the CFOs at Fortune 500 and S&P 500 companies stay in their posts for less than three years, according to this Financial Week report.

According to the study, churn is getting worse with the average tenure for CFOs at all big companies slipping to under five years, about a year less than in 2006.

What's causing it? Obviously a more volatile market means you have more directors and shareholders jumping at shadows. Also, more CFOs are going for where the bucks are at private equity outfits. And both of those trends are expected to continue.

Still, there aren't that many CFOs to go around which means a combination of volatility and the magnet of private equity will ensure they will continue to earn mega-salaries.