Reality Check: No Evidence that Gerrymandering Benefits Republicans More than Democrats

Gerrymandering is a term that dates back to 1812 when Massachusetts Governor Elbridge Gerry created an oddly-shaped district resembling a salamander and so, this portmanteau word was coined by combining the words Gerry and salamander. Since then, there have been many claims that the entire map of U.S. Congressional districts, or a significant part, gives an unfair advantage to a certain political party or to an ethnic, religious, or racial group by manipulating the district boundaries. Because there are 435 congressional districts in the country, some or many of such claims pertaining to specific districts are undoubtedly justified. However, is there any reason to believe that, overall, gerrymandering tends to benefit the Republicans more than the Democrats, as is often claimed?

There are several studies devoted to gerrymandering. Some of them offer convoluted models and statistical criteria that are applied to cherry-picked regions. Others reference court cases pertaining to specific districts. Luckily, there is a simple and precise mathematical way of testing claims that there is a systemic bias in the district boundaries that favors one major party over the other nationwide. This test is based on the fact that gerrymandering, by definition, may affect only the House, as each Senator is elected by the popular vote in his or her entire state. Since most state boundaries were drawn in the 18th and 19th centuries when states’ demographics were quite different from what they are now, it is hard to imagine that these boundaries were established to influence elections two centuries later. Therefore, it is safe to assume that senatorial elections are absolutely free from gerrymandering and the composition of the Senate may be used as a yardstick for detecting any systemic partisan gerrymandering of House districts nationwide.

If the claim of systematic gerrymandering mostly in favor of the Republicans were correct, then Republicans would have a clear advantage in the House compared to the Senate.  In fact, the opposite is true: the most recently elected House has a clear majority of Democrats, whereas the Senate has a clear majority of Republicans.

But let’s play devil’s advocate now. House members are elected for two years and Senators for six. One may argue that the composition of the House reflects the current mood in the electorate more accurately than that of the Senate, because while all House members were re-elected in November 2018, only one-third of senators were re-elected.  So one cannot compare the current compositions of the two chambers, as they reflect the mood of the country at different points in time.

To address the question of whether systematic gerrymandering favoring the Republicans exists, we need to consider a larger sample. Let’s compare the composition of the Senate with that of the House for the past 40 years, starting with the 97th Congress elected in 1980 and ending with the 116th Congress elected in 2018  (Congresses are numbered sequentially and the numbers are incremented biannually). The following chart depicts these 20 data points. The individual points are widely available. See, for example, the 20 articles from this to this.

Traditional colors are used, red for Republican-controlled chambers and blue for Democratic-controlled chambers. In two Congresses, the 107th and 110th, the Senate is depicted in gray, as its control was “too close to call.” The control of the Senate in the 107th Congress changed hands several times because a senator died and another senator changed his party affiliation. Neither party had a majority in the Senate of the 110th Congress, because two senators were independent. For organizational purposes, they caucused with the Democrats, but one of them, Joe Lieberman, actively campaigned for John McCain, the Republican who ran for president in 2008 when Lieberman caucused with the Democrats.

If we exclude the two “gray” cases, the remaining 18 cases may be summarized as follows:

1. Most of the time, the same party has controlled both chambers: the Republicans 7 times and the Democrats 5 times.
2. The Democrats have controlled the Senate while the Republicans have controlled the House – which is the situation supporting the hypothesis of gerrymandering in favor of the Republicans – twice.
3. The Republicans have controlled the Senate while the Democrats have controlled the House – which is the situation supporting the hypothesis of gerrymandering in favor of the Democrats – 4 times.

In conclusion, this statistical analysis shows no evidence of systematic gerrymandering predominantly benefitting Republicans. If anything, it provides more evidence of gerrymandering in favor of Democrats, although the evidence is statistically insignificant: 4 to 2 out of 20. The discrepancy is more likely due to the fact that many people cast their votes for candidates on the basis of the candidates’ individual qualities, rather than their party affiliations, which, by the way, is a good idea.

It is entirely possible that certain Congressional districts are gerrymandered, but there is no evidence that this phenomenon benefits Republicans more than Democrats. Another urban myth is debunked.