Donald Trump is the outperformer in most Republican presidential polls going into Super Tuesday, but he may be an underperformer in real estate after 40 years of dealmaking. Would he be a better president than property manager?

“Mr. Trump has underperformed the real estate market by approximately $13.2 billion, or 57%,” since 1976, says John Griffin, a finance professor at the University of Texas, who compared Trump’s stated net worth with four decades of returns on the FTSE NAREIT All Equity REITS FNERXXXX, -1.98% Index.

The NAREIT index, developed in the early 1970s by the Washington-based trade group the National Association of Real Estate Investment Trusts, tracks the performance of publicly traded real estate investment companies that own commercial properties, such as offices, hotels and apartments.

Starting with Trump’s professed net worth of “more than $200 million” in an interview published by The New York Times in November 1976, Griffin says the FTSE NAREIT All Equity REITS Index-compounded return would have returned $23.2 billon at the end of 2015, “considerably above Mr. Trump’s recent self-reported net worth of approximately $10 billion.”

Rather than rely on Trump’s word alone, Griffin also calculated the developer’s returns based on two independent assessments of his wealth: A BusinessWeek estimate that he was worth $100 million in 1978, and Forbes magazine’s analysis that puts his current fortune at about $4.5 billion.

Starting with the BusinessWeek number, the NAREIT index would have returned $8.6 billion by the end of last year, which is nearly double the Forbes estimate and consistent with “an underperformance of 48%,” Griffin says.

One caveat is that the NAREIT index doesn’t take into account living expenses and taxes. It’s not possible to estimate Trump’s real-estate tax rate, as he has not released his personal income taxes. Real estate investors pay no income tax so long as they roll any asset sale into a like-kind real estate venture.

However, Griffin also points out that investing in a passive REIT also has a cost: At an average expense ratio of 1.03%, a $23 billion REIT position would cost the investor about $230 million a year in fees, an amount that would go a long way toward meeting living expenses.

“These numbers,” Griffin adds, “do not take into account leverage. The REIT equity funds have current leverage rations around 36%, while Trump is documented to have been levered to 69%. If one were to lever the REIT returns at Trump’s rate, then the index’s performance would be considerably higher.”

So “not only is the $13.2 billion a potential understatement of Trump’s underperformance,” Griffin concludes, “but also it seems he needed to take on a market-exceeding amount of risk in order to achieve his performance.”