From the Introduction: "The party ratio in a House of Representatives standing committee refers to the proportional number of members of each party caucus assigned to each committee. Determining sizes, ratios, and committee assignments are among the first actions taken following a general election and at the beginning of a Congress. The Standing Rules of the House of Representatives are silent regarding committee sizes and party ratios; the apportionment of committee seats is a decision of the majority leadership that may include discussions between majority and minority party leaderships occurring during early organization meetings. Historically, the number of majority seats on most committees has exceeded, in varying degrees, the strength of the majority party in the House chamber, regardless of which party has been in power. In instances of close party division in the House chamber, the majority party has ensured that it has a majority sufficient to guarantee party control in committees. The exception has been the House Committee on Standards of Official Conduct, for which House Rules guarantee an equal share of the seats to the two parties. While individual committees' ratios may vary substantially from the proportional number of majority and minority Members of the House, the aggregate number of seats better reflects the proportion in the chamber itself, while still favoring the majority party. This report shows House committee party ratios for 17 Congresses from the 98th Congress (1983-1985) through the 114th Congress (2015-2017). Tables for each Congress include the standing committees and a permanent select committee as established and named in each Congress. An additional table provides a comparison of majority party strength in the House chamber and total committee seats."
CRS Report for Congress, R40478
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html