New York (CNN Business) Executives of America's large public companies have long played a role in public policy by advising leaders of both parties — but those corporate chieftains themselves are far more likely to be Republicans than Democrats, a new study shows.

In a working paper released this month by the National Bureau of Economic Research, researchers at Harvard Law School and Tel Aviv University ran the names of all individuals to have run a company listed in the S&P 1500 between 2000 and 2017 through federal campaign finance databases, which include contributions to both congressional and presidential candidates as well as party committees.

The result: 18.6% of CEOs consistently donated to Democrats, while 57.7% donated to Republicans, with the rest leaning toward neither party.

That may not be surprising, given how big business tends to benefit more from conservative policy goals like lowering taxes and easing up on regulations. Labor unions donate heavily to Democrats, who tend to support more worker-friendly policies.

But the research shows just how deep those preferences run, and it further explores the wider implications at a time when corporations spend vast sums of money on elections.

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