The American National Election Studies conducts periodic research on the opinions of U.S. voters. The accompanying table shows the percentage of people, in selected years from 1952 to 2012, who agreed with the statement “There are important differences in what the Republicans and Democrats stand for.”

What do these data say about the degree of partisanship in U.S. politics over time?

Year                Agree with statement
1952.............................................50%
1972................................................46
1992................................................60
2004................................................76
2008................................................78
2012................................................81