Beautiful Data

Example 4: Public Opinion and Senate Voting on Supreme Court Nominees

Few decisions made by U.S. senators are as visible to the public as votes to confirm or reject a Supreme Court nominee. Whereas the outcomes of many Senate votes, such as spending bills or the modification of a statute, are ambiguous or obscured in procedural detail, the result of a vote on a Supreme Court nomination is stark: either the nominee is confirmed, allowing her to serve on the nation's highest court, or she is rejected, forcing the president to name another candidate (Kastellec et al. 2008). Do senators follow state-level public opinion when casting such votes?

Figure 19-4 presents a preliminary answer to this question by graphing the relationship between state-level public opinion on nine recent Supreme Court nominees and senators' votes on whether to confirm those nominees. On each graph, the curve shows the probability that a senator votes to confirm the nominee as a function of public opinion in the senator's state. The solid black line displays the estimated curve from a fitted logistic regression, and the clusters of light-gray lines depict uncertainty in this estimation. The hash marks (or "rugs") indicate votes of approval ("1") and rejection ("0") of nominees, while the numbers in the lower-right corner of each plot denote the overall vote tally by the Senate. The bottom plot pools all nominees together. We order the plots across and down by increasing mean support for each nominee.

Figure 19-3. Some ...