How the Vote Ratings Are Calculated

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Feb. 5, 2014, 11:59 p.m.

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 long­time con­trib­ut­or to Na­tion­al Journ­al.

For the 2013 rat­ings, Na­tion­al Journ­al ex­amined all of the roll-call votes in the first ses­sion of the 113th Con­gress — 641 in the House and 291 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, 117 votes in the Sen­ate and 111 votes in the House were se­lec­ted and were cat­egor­ized as eco­nom­ic, for­eign, or so­cial.

As in oth­er years re­cently, eco­nom­ic is­sues dom­in­ated the House’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). The Sen­ate voted on more so­cial is­sues than the House be­cause of its con­sid­er­a­tion of im­mig­ra­tion and gun-con­trol meas­ures.

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 2013. 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 and for­eign cat­egor­ies in the Sen­ate last year. Many mem­bers had the same scores be­cause they voted alike. In the eco­nom­ic cat­egory, there were few­er ties.

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 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, con­sider the hy­po­thet­ic­al ex­ample of a vote in the House on cut­ting do­mest­ic spend­ing. Let’s say the bill passed with over­whelm­ing sup­port from House Re­pub­lic­ans and over­whelm­ing op­pos­i­tion from House Demo­crats. A vote for the bill would be coun­ted as con­ser­vat­ive and a vote against the bill would be coun­ted as lib­er­al. But let’s say a hand­ful of House Re­pub­lic­an con­ser­vat­ives voted against the bill on the grounds that the budget cuts didn’t go far enough. In so do­ing, they voted against most con­ser­vat­ives and with most lib­er­als. Their votes would be 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. For that reas­on, some high-pro­file votes that have con­ser­vat­ives vot­ing against a meas­ure be­cause it isn’t con­ser­vat­ive enough and lib­er­als vot­ing against the same meas­ure be­cause it isn’t lib­er­al enough are of­ten omit­ted from the vote rat­ings.

Na­tion­al Journ­al‘s an­nu­al 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, such as lead­er­ship and ef­fect­ive­ness.

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