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How the Vote Ratings Are Calculated How the Vote Ratings Are Calculated

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How the Vote Ratings Are Calculated

For the past three decades, National Journal has rated members of Congress based on selected roll-call votes from the previous year to see how they compared with each other on an ideological scale. Unlike interest groups that rate lawmakers, National Journal does not attempt to say how members should have voted. Our goal is to describe how they voted in comparison with one another.

The ratings system was devised in 1981 under the direction of Bill Schneider, a political analyst and commentator, and a contributing editor to National Journal.


For the 2012 ratings, National Journal examined all of the roll-call votes in the second session of the 112th Congress—659 in the House and 251 in the Senate—and identified the ones that show ideological distinctions between members. Many votes did not make the cut—those that involve noncontroversial issues or that fall along regional lines, for instance. In the end, 116 votes in each chamber were selected and were categorized as economic, foreign, or social.

As in other years recently, economic issues dominated Congress’s attention; there were fewer votes on social issues (such as abortion rights or gun control) and foreign issues (such as war funding and foreign aid).

Lists were downloaded from the House and Senate websites showing how all the members voted on the selected votes. The votes in each issue area were then subjected to a principal-components analysis, a statistical procedure designed to determine the degree to which each vote resembled other votes in the same category (the same members tending to vote together).


The analysis also revealed which yea votes correlated with which nay votes within each issue area (members voting yea on certain issues tended to vote nay on others). The yea and nay positions on each roll call were then identified as conservative or liberal.

Each roll-call vote was assigned a weight from 1 (lowest) to 3 (highest), based on the degree to which it correlated with other votes in the same issue area. A higher weight means that a vote was more strongly correlated with other votes and was, therefore, a better test of economic, social, or foreign policy ideology. The votes in each issue area were combined in an index (liberal or conservative votes as a percentage of total votes cast, with each vote weighted 1, 2, or 3).

Absences and abstentions were not counted; instead, the percentage base was adjusted to compensate for missed roll calls. A member who missed more than half of the votes in any issue category was scored as “missing” in that category (shown as an asterisk [*] in the vote-rating tables).

Members were then ranked from the most liberal to the most conservative in each issue area. These rankings were used to assign liberal and conservative percentile ratings to all members of Congress.


The liberal percentile score means that the member voted more liberal than that percentage of his or her colleagues in that issue area in 2012. The conservative figure means that the member voted more conservative than that percentage of his or her colleagues.

For example, a House member in the 30th percentile of liberals and the 60th percentile of conservatives on economic issues voted more liberal than 30 percent of the House and more conservative than 60 percent of the House on those issues, and was tied with the remaining 10 percent. The scores do not mean that the member voted liberal 30 percent of the time and voted conservative 60 percent of the time.

Percentile scores can range from a minimum of 0 to a maximum of 100. Some members, however, voted either consistently liberal or consistently conservative on every roll call. As a result, there are ties at both the liberal and the conservative ends of each scale. For that reason, the maximum percentiles are usually less than 100. This was most apparent in the social category in the Senate last year. Many members had the same scores because they voted alike on the relatively few number of votes. In the economic category, there were fewer ties because there were more votes.

Members also receive a composite liberal score and a composite conservative score determined by their issue-based scores. Members who missed more than half of the votes in any of the three issue categories do not receive composite scores (shown as an asterisk [*] in the vote-rating tables).

To determine a member’s composite liberal score, for example, first add the liberal scores in all three issue areas. Next, in each issue area, calculate 100 minus the member’s conservative score and add the three results together. The two figures are then combined and divided by 6 (the number of individual scores).

Critics have sometimes accused National Journal of rigging the vote ratings so that certain members of Congress are ranked as the most liberal or most conservative. The criticism is unfounded. When we select the votes, we have no any idea how an individual member of Congress will be ranked.

Keep in mind that no single measure of voting behavior is likely to be perfect. For instance, some House Republicans occasionally voted against budget-cutting measures last year because they didn’t think the bills reduced spending enough. In so doing, they voted against the overwhelming majority of House conservatives and with the overwhelming majority of House liberals (who opposed the measures because they thought the bills cut spending too much). In such cases, their votes were counted as liberal because they voted with liberals. It’s beyond the capacity of a vote ratings system to determine why a member voted the way he or she did on any particular piece of legislation.

National Journal’s vote ratings, like any other vote ratings, should be viewed as a tool in assessing a member of Congress but not the only tool. Other vote ratings should also be taken into consideration, as should attributes beyond the capability of a rating system to assess qualities, such as leadership and effectiveness.

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