For the fourth consecutive year, U.S. Sen. Susan Collins, R-Maine, has been rated the most bipartisan legislator in the United States Senate by a ranking index.

Each year The Lugar Center and Georgetown University’s McCourt School of Public Policy produce a nonpartisan ranking of how often each member of Congress works across party lines. The 2017 first-place finisher turned out to be Collins.

U.S. Sen. Angus King, I-Maine, was ranked 25th by the Bipartisan Index.

“In today’s highly charged partisan atmosphere, it is more difficult than ever to find common ground,” Collins said in a statement issued Wednesday. “Given how divided our country has become, I feel a special obligation to try to find a path forward on the many contentious issues we are facing.”

The ranking is based on voting records as well as the frequency with which a member sponsors bills that are co-sponsored by at least one member of the opposing party.

The Lugar Center, under the leadership of former U.S. Sen. Richard Lugar, an Indiana Republican, is a nonprofit organization that promotes debate on global issues.