Courts are behind the times when it comes to reviewing merger cases, making it harder for regulators to block the ones that may harm competition, according to an antitrust lawyer who recently left a senior post at the Federal Trade Commission.

Speaking to a gathering of fellow antitrust attorneys on Wednesday, Susan Creighton, formerly the head of the FTC’s Bureau of Competition and now a partner at Wilson, Sonsini, Goodrich & Rosati, said federal judges continue to base merger review decisions on court precedents established in the 1960s that emphasize the number of players remaining in a market post-merger.