Almost 40 percent of U.S. corporate directors with responsibility for monitoring the profit-and-loss ledger have social ties to the chief executive, a study says, making them look more like lapdogs than watchdogs.

Conducted by two accounting professors at Tilburg University in The Netherlands, the study reinforces long-held perceptions of a clubby culture on U.S. corporate boards, where members seldom challenge the executives they are meant to police.

The study looked at about 2,000 U.S. companies and their board audit committees, which are responsible for overseeing outside auditors and making sure financial reports are accurate. It found that personal friends of senior managers were often appointed to these committees, making the directors more likely to go along with the company’s reporting practices.

Where that was the case, earnings manipulation was more frequent and problems such as weak financial controls were covered up, the study found.

Regulations put in place over a decade ago after accounting scandals at Enron and WorldCom required audit committees to be made up only of independent directors. That meant they were never employed by the company or a firm doing business with it.

Even so, audit committee members often have long-standing social ties to executives, belonging to the same elite clubs or charity boards, the study found.

“Although such firms appear to have independent audit committees, in reality these committees offer little to no monitoring at all,” the study found.

The study, by accounting professors Liesbeth Bruynseels and Eddy Cardinaels, researched social ties with BoardEx, a business intelligence service. It appears in the January 2014 issue of the American Accounting Association’s Accounting Review.

The professors suggested that legislators consider requiring more disclosure about social connections between audit committees and CEOs, given the committees’ importance.

Charles Elson, director of the Weinberg Center for Corporate Governance in Newark, Delaware, said it would be difficult for regulators to define social ties.

“Is it one lunch a week, is it two lunches? Inevitably, social ties will develop when you’re on a board—you have to see that person on a regular basis,” he said.

The United States made a major push to improve audit committees’ effectiveness with the passage of the 2002 Sarbanes-Oxley Act, which tightened membership requirements.

More recently, regulators in Europe and the United Kingdom have been trying to get audit committees to be more rigorous in choosing outside auditors and monitoring them. (Additional reporting by Huw Jones in London; Editing by Kevin Drawbaugh and Dan Grebler)