CRS – Congressional Careers: Service Tenure and Patterns of Member Service, 1789-2015. Matthew Eric Glassman, Analyst on the Congress; Amber Hope Wilhelm, Graphics Specialist. January 3, 2015

The average service tenure of Members of the Senate and House of Representatives has varied substantially since 1789. This report presents data on Member tenure and a historical analysis of tenure trends. During the 19th century, the average service of Representatives and Senators remained roughly constant, with little or no change over time; the average years of service was slightly higher for the first half of the century than during the second. During the late 19th and through the 20th century, the average years of service for Senators steadily increased, from an average of just under five years in the early 1880s to an average of just over 13 years in recent Congresses. Similarly, the average years of service of Representatives increased from just over four years in the first two Congresses of the 20th century to an average of approximately 10 years in the three most recent Congresses. The average years of service for Members of the 114th Congress, as of January 6, 2015, when the Congress convened, was 8.8 years for the House and 9.7 years for the Senate. The average years of service for Members of the 113th Congress, as of January 3, 2013, when the Congress convened, was 9.1 years for the House and 10.2 years for the Senate. The average years of service for Members of the 112th Congress, as of January 5, 2011, when the Congress convened, was 9.8 years for the House and 11.4 years for the Senate. Two underlying factors appear to influence variation over time in the average years of service for Members of Congress: the decision of sitting Members whether or not to seek election to the next Congress, and the success rate of Members who seek election to the next Congress. In addition, short-term variation in average service is affected by the individual service tenures of Members who do not return for the following Congress. Observed increases in the proportion of Members seeking re-election and decreases in the proportion of Members defeated for re-election conform with previous scholarly assessments of congressional history, which largely conclude that during the early history of Congress, turnover in membership was frequent and resignations were commonplace, and that during the 20th century, congressional careers lengthened as turnover decreased and Congress became more professionalized. The report also examines two further issues related to Member tenure. First, the distribution of Member service that underlies the aggregate chamber averages is examined. Although the average service tenure of Members has increased, more than half of Representatives and Senators in recent Congresses have served eight years or less. Second, the report analyzes historical trends in the percentage of Members who have served in both chambers. While only a small and declining proportion of Representatives have historically had previous Senate experience, throughout history a sizeable percentage of Senators have previously served in the House.”