From the Summary: "The party ratio in the Senate standing committees is the proportional number of members of each party caucus assigned to each committee. Determining committee sizes, ratios, and assignments are among the first actions taken after a general election and at the beginning of a Congress. [...] This report shows Senate committee party ratios for 20 Congresses, covering the period of the 98th Congress (1983-1985) through March 2021, the first part of the 117th Congress (2021-2023)."
CRS Report for Congress, RL34752
Congressional Research Service: https://crsreports.congress.gov/