The compensation that CEOs at America's largest firms received in 2015—$15.5 million—was only 276 times the average worker's salary for that year, according to a report by Lawrence Mishel and Jessica Schieder of the Economic Policy Institute. We say "only" because the ratio was an even loftier 303 in 2014, but according to the report, last year's decline does not indicate a broader trend towards more equitable compensation practices.

The gap between typical workers' earnings and those of their C-suite colleagues has ballooned in recent decades. A large company's CEO might earn 20 times more than the average employee in 1965. The multiple crept up during the 1970s and 1980s, reaching 112 in 1993. Then it more than tripled in under a decade, hitting a record 376 in 2000. (For more, see also: Funds Should Vote Down More CEO Pay Packages: Poll.)

Since that time changes in CEO pay have broadly mirrored the fortunes of the S&P 500, plummeting after the dot-com bust, rising again during the subsequent recovery, and repeating the cycle in the wake of the subprime mortgage crisis. Since average workers' earnings barely budged during this period—rising an inflation-adjusted 10.3% in the 37 years to 2015—the CEO-to-worker pay ratio followed a basically identical trajectory (inflation-adjusted CEO pay increased by 940.9% over the same period). (For related reading, see also: CEOs Get a Raise. Workers, Shareholders Wonder Why.)

Source: Economic Policy Institute.

The stock market also accounts for the decline in the CEO-to-worker pay ratio between 2014 and 2015. Because the majority of executive compensation is awarded in the form of stock options, a turbulent year for equities depressed CEO pay. According to the report, however, it "can be expected to resume its sharp upward trajectory when the stock market resumes rising." (For more, see: CEO Pay Packages at Top 5 U.S. Banks.)

Mishel and Schieder reject arguments that the increase in executive pay is justified by higher productivity, talent, education or market forces. They point out that CEO compensation is growing faster than that of the top 0.1% of wage earners and of college graduates. Their conclusion is that the primary reason for the trend is CEOs' "rent-seeking behavior."

See original article: CEO Pay: Don't Believe the Headlines (Even Ours)

As for solutions, the authors prescribe reinstating higher marginal income tax rates for top earners, removing the tax break for executive pay, rising corporate tax rates for firms with higher CEO-to-worker pay ratios, and allowing firms' shareholders to vote on top executives' compensation.

Shareholders—including some of the world's largest—are becoming increasingly vocal about the issue of CEO compensation, particularly when companies' performance and their bosses' paychecks diverge (for example, BP, NantKwest and Valeant).

Want to learn how to invest?

Get a free 10 week email series that will teach you how to start investing.

Delivered twice a week, straight to your inbox.