Many western democracies limit the power of their politicians to control the electoral boundaries to avoid the possibility of gerrymandering. UK electoral boundaries, for example, are redrawn when required by an independent commission. Many US states, however, put the boundaries entirely under the control of elected politicians and this often results in some fairly odd boundaries.

Some regard this as self-evidently bad. For example, the following argument is made on www.fairvote.org:

Redistricting encourages manipulation of our elections by allowing incumbent politicians to help partisan allies, hurt political enemies and choose their voters before the voters choose them. The current process is used as a means to further political goals by drawing boundaries to protect incumbents and reduce competition, rather than to ensure equal voting power and fair representation.

Some states have had non-political control for some time (Iowa, for example) and others have recently enacted citizen driven initiatives to remove the power from politicians (eg California). (see this CNN report for some examples).

It seems likely that gerrymandering will strengthen incumbents. But what does the evidence say? How much does it increase electoral security for incumbents?

  • 3
    I'm confused by what is being asked, sorry. This seems to be fishing for a positive outcome, any positive outcome, to an act which is against the values of many/most people. The act of putting political self-interest above the right to equal representation (a moral value, not a scientific fact) makes the act of gerrymandering ethically wrong (to many), no matter what the unintended outcomes. Asking the equivalent to "Surely we can think of some good outcomes of murder?" seems to miss the point.
    – Oddthinking
    Oct 18, 2012 at 22:34
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    I was hoping to focus on the demonstrable effects of gerrymandering in order to avoid the debate on values which would be off topic. A concrete link to more secure incumbents or stronger polarisation should be statistically demonstrable (if true) and doesn't require a value judgement.
    – matt_black
    Oct 18, 2012 at 22:41
  • Perhaps we can narrow this down then to one of those two, and lose the "ensuring minorities get (disproportionate) representation, and other positives" angle? You seem to have already answered the polarisation claim yourself, so should the question be "Is gerrymandering successful at securing incumbents in office?"?
    – Oddthinking
    Oct 18, 2012 at 22:46
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    Far too many assumptions in this question, and far too much vagueness in the expected answer. Is gerrymandering "bad"? Not something we can answer here. Oct 19, 2012 at 15:51
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    While it is not evidence in the Skeptics.SE sense, the very way that politicians squabble over redistricting suggests that they believe it matters. Two possible avenues of research would be looking at incumbent retention rates as a function of time since the last redistricting (probably a small effects, but there is potentially a lot of data) and compare the retention rates in the (say) decade before and after California's move to a "non-partisan" commission (if we have any idea what non-partisan means and how it can be assured on a on-going basis). Oct 19, 2012 at 19:01

1 Answer 1


Yes, strategic redistricting (gerrymandering) can make incumbents more secure.

I'm basing my answer on the Redistricting series by ProPublica.

District boundaries can have an effect on election outcomes:

The maps used in Texas’ next elections could impact the balance of power in Congress. They will likely determine whether the four new congressional seats awarded Texas via the census will be held by Democrats or Republicans. (Actual Winner Unclear in Supreme Court’s Ruling on Texas Redistricting)


[H]ow the district lines are drawn is likely to determine whether those additional seats will be won by Democrats or Republicans -- and how big an impact minority voters will have in deciding who the new representatives will be. (Will the Supreme Court Strike Down Part of the Voting Rights Act?)

The line drawing can be done in a way so as to intentionally benefit a particular party or individual:

As it has done before, the Republican-dominated state legislature drew maps that heavily favor Republicans. (Ibid.)

[P]oliticians have been drawing district lines for their own advantage since the days of the founding fathers, when Patrick Henry gerrymandered a Virginia district to try to keep James Madison out of Congress. (Is Partisan Gerrymandering Unconstitutional?)

The right lines can all but guarantee an incumbent a decade's worth of electoral success, or alternatively can help send others into retirement. (Redistricting, A Devil's Dictionary)

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