1994 is a pretty clear demarcation. That year was a Republican wave that brought the party back to power in the House for the first time in four decades. Since that election, only once, in 2008, has the GOP had a lower percentage of the vote than seats. In every other election, it’s secured a greater percentage of seats than it has a percentage of votes.

Interestingly, that ratio hasn’t been as beneficial for the GOP in the last two elections. They’ve been two of the four least unbalanced elections since 1994.

Why is this happening? One factor may simply be that the GOP is earning a higher percentage of the national House vote than it used to. From 1960 to 1992, it earned an average of 45 percent of that vote. Since, it’s earned an average of 48 percent. Because the percentage of votes cast is necessarily more finely represented than the percentage of House seats (you can’t win precisely 50 percent of House seats, for example) that necessarily means that there will be some disconnect in most years.