Alleged wrongdoing by stockbrokers is routinely erased from public records, making it difficult for investors to check the past conduct of financial advisers, according to a new study.

The report found that stockbrokers almost always succeed in getting negative information removed from a database known as BrokerCheck.

BrokerCheck is intended to protect investors against unscrupulous brokers. It lists brokers’ complaints from customers and investigations by regulators. BrokerCheck is operated by the Financial Industry Regulatory Authority (FINRA), an oversight organization operated by the securities industry.

After settling a legal dispute with a client, a broker can apply to have the complaint itself eliminated from public records. So-called expungement decisions are made by arbitration panels that preside over the disputes.

Arbitrators are supposed to delete broker records only in rare cases, the study says. Instead, it appears to be common.

From mid-May 2009 through 2011, brokers were granted expungement in 96.9 percent of cases, according to the report by the Public Investors Arbitration Bar Association, or PIABA.

One broker requested expungement 40 times. It was granted 35 times, the study found.

“To say that ‘expungement’ of customer claims from broker records is a major investor protection problem is an understatement,” said Scott Ilgenfritz, the president of association. “The result is that investors who are diligent enough to seek out information about brokers may be getting a woefully incomplete picture of the individual to whom they will entrust all or most of their nest egg.”

The Public Investors Arbitration Bar Association is a trade group for lawyers who represent investors in cases against brokers. The study analyzed cases from 2007 through 2011.

In a statement, FINRA, the oversight organization, expressed concern about the deletion of broker records.

“PIABA’s study underlines and emphasizes serious concerns FINRA shares with respect to the expungement process.

“As a result of these concerns, FINRA recently provided expanded guidance to assist arbitrators in the proper performance of their responsibilities with respect to expungement, and is enhancing arbitrator training with added emphasis on the importance of the integrity of the information” in the system.