Barry Ritholz has an excellent article on executive compensation. I say "compensation" because CEOs get paid more, much more, than their salary. And it's gotten worse. The Economic Policy Institute reports, “CEO pay grew an astounding 943% over the past 37 years.” EPI further observes this was a far faster growth rate than “the cost of living, the productivity of the economy, and the stock market.”
Another study - this by the research firm Audit Analytics. More companies report executive pay using non-GAAP accounting. And it's getting worse; last year 58% of the S&P companies used non-GAAP, five years ago only 27% did.
A Harvard Law School study:
The 10 companies identified as the most overpaid firms as a group underperformed the S&P 500 index by 10.5% and actually demolished shareholder value as a group with –5.7% financial returns.