A growing number of underperforming companies want investors and analysts to know: “Our top executives aren’t making as much money as you think they are.”

In this era of unrest over executive pay, the compensation data required to be disclosed in proxy statements may portray company leaders as being unduly enriched while performance lags, a study by Compensation Advisory Partners (CAP) suggests.

Among the various types of compensation that must be included in proxies, stock optionsand restricted stock are valued based on their grant-date values (most often using the Black-Scholes valuation model, in the case of stock options). Therefore, executives with out-of-the-money options or restricted stock appear to have earned more than they did.

So some companies are offering voluntary supplemental disclosure, in the form of “realized” or “realizable” pay. With the former, the actual gain an executive realized upon exercising stock options is reported, says Eric Hosken, a partner with Compensation Advisory Partners. Restricted stock is reported as the value of an award upon its vesting date. If no options were exercised during the year or no restricted stock vested, no value for those items is reported.

With realizable compensation, options and restricted stock are valued at year-end regardless of whether the executive exercised any options or had any restricted stock that vested.

Looking at publicly held Fortune 500 companies, CAP determined that 8.6 percent and 7.0 percent of them disclosed realized and realizable pay, respectively, in the 2013 proxy season. Two years earlier, almost no companies did so, Hosken says. (A mere 0.9 percent used both measures.)

CAP notes that for about 90 percent of companies disclosing realized pay and “a majority” of those disclosing realizable pay, executives’ income (as compared to total shareholder return, or TSR) appeared to be higher when looking at the mandated compensation data.

“It’s a way to say look, our pay may look high relative to TSR when you look at the summary comp tables in the proxies, but if you look at our realized or realizable pay, you’ll see that it’s in alignment,” says Hosken.

As for reasons behind the trend of reporting realized and realizable pay, in addition to shareholder unrest Hosken notes that “there are some hints that under Dodd-Frank there’s going to be enhanced disclosure of the pay-performance relationship, which may go in the direction of realized and realizable pay.”