Hidden Representation in Bicameralism: Petitions, Second Chambers, and Complementary Representation in the Japanese Diet

This article examines petitions as channels of complementary representation under bicameralism. Complementary representation refers to cross-chamber differentiation in the institutional pathways through which citizens’ and groups’ demands are connected to parliament, formally recognized, and processed without necessarily producing policy change. Using 15,674 petitions submitted to the Japanese Diet between 2001 and 2025, the article compares petition adoption and functions in the House of Representatives (H.R.) and the House of Councillors (H.C.). Although raw adoption rates differ little, the full-period controlled model yields average predicted adoption probabilities of 5.9 percent for H.C. petitions and 3.2 percent for H.R. petitions. The negative H.R. coefficient remains significant in several full-period specifications, including a title-only analysis, but is smaller under title-only classification. The adoption difference is concentrated before the 210th Diet, while functional differences are sensitive to textual comparability. The findings extend bicameralism research beyond inter-chamber bargaining by showing that second chambers can provide distinct institutional pathways through which social demands become visible and formally recognized. They also identify the production and availability of parliamentary records as an important measurement condition for comparative research on representative functions.