Curtis Gans, 77, a liberal activist, journalist, and recognized expert on voter turnout in the United States, has died.

Mr. Gans, a northern Virginia resident, died of lung cancer Sunday night at a hospital in Frederick, Md., said his only son, Aaron Gans.

Mr. Gans was cofounder, with Allard Lowenstein, of the "Dump Johnson" movement, which sought an alternative to President Lyndon B. Johnson in 1968 because of his policies on Vietnam. Johnson withdrew his candidacy, a rarity for a sitting president.

Mr. Gans went on to found the Committee for the Study of the American Electorate, which provided data and analysis of voter turnout.

The organization later became affiliated with American University in Washington as the Center for the Study of the American Electorate, with Mr. Gans as director.

He was the author of Voter Turnout in the United States, 1789-2009, and he wrote syndicated newspaper columns.

Born in New York, Mr. Gans became active in the civil-rights movement while at the University of North Carolina, where he edited the student newspaper.

In 1960, he participated in the Greensboro sit-ins, which led the Woolworth department store to end its segregationist policies. He also took part in the 1965 civil-rights march in Selma, Ala.

- AP