This chart is designed to show changes in the party unity scores in both the House and Senate from 1954 to 2002. The X-axis represents the year; the Y-axis, party unity scores by percentage. The four graph lines represent the unity scores of House Democrats, House Republicans, Senate Democrats, and Senate Republicans. Overall, party unity scores were low during the 1970s compared with the previous decades and with the period since the 1980s. The recent period denotes a significant increase in party unity within House Republicans followed by House Democrats, while both parties in Senate indicate relatively lower unity scores than the House. <p> Note: Data shows percentage of members voting with a majority of their party on party unity votes. Party unity votes are those roll calls on which a majority of Democrats vote against a majority of Republicans. Percentages are calculated to eliminate the impact of absences as follows: (unity)/(unity+opposition).