format
A 401-by-669 matrix whose ($i$,$j$)-entry corresponds to the vote of the $i$th representative on the $j$th roll call. Possible votes are "yea", "nay", or "not voting", which are represented by 1/2, -1/2, and 0, respectively.source
Diaconis PD, Goel S, and Holmes S (2008). Horseshoes in Multidimensional Scaling and Local Kernel Methods. Annals of Applied Statistics. 2 (3) 777-807. Supplementary material.