Comparing Cosponsorship and Roll‐Call Ideal Points

We use bill cosponsorship and roll‐call vote data to compare legislators' revealed preferences in the U.S. House of Representatives and the Argentine Chamber of Deputies. We estimate ideal points from bill cosponsorship data using principal‐component analysis on an agreement matrix that included information on all bills introduced in the U.S. House (1973–2000) and Argentine Chamber (1983–2002). The ideal‐point estimates of legislators' revealed preferences based on cosponsorship data strongly correlate with similar estimates derived from roll‐call vote data. Also, cosponsorship activity in the U.S. House has lower dimensionality than cosponsorship has in the Argentine Chamber. We explain this lower discrimination as a function of individual‐ and district‐level factors in both countries.