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Cox: Electoral rules and electoral coordination

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Cox. 1999. Electoral rules and electoral coordination. ARPS (2):145-61.

In Brief

Electoral coordination occurs at two levels: (a) at the district level and (b) at the national level. We know quite a bit about (a) (see Cox 1997), but far less about (b). (There is also a third level: coordination to distribute porfolios (in the cabinet or committee chairmanships), but Cox decides not to discuss that.)


These are all based on ENPP:

  • District level: Use ENPavg, the average ENP in each district (measure by district)
  • National level: Use ENPnat, the national ENP.

To measure linkage (b), use an inflation factor to measure how much higher ENPnat is than ENPavg. If I = 10, then about 10% of the size of ENPnat can be attributed to poor linkage (i.e. localized parties). Perfect linkage would have I = 0:

  • I ("eye") = 100*(ENPnat - ENPavg) / ENPnat

(a) THE DISTRICT LEVEL: Two distinct M+1 rules.


This is where most of the action is: Parties, factions, and groups must decide who will run candidates--and how many each faction will run. They will coordinate in a Duvergerian manner (using Cox's M+1 rule) when three conditions hold (illustrated in a first-past-the-post district, but true elsewhere):

  1. Everyone agrees that only two (M+1) parties have a realistic chance of winning. If we think that an extra party has a good chance, then there will be too many candidates.
  2. Everyone agrees about which parties have the most realistic chances of winning.
  3. We have short-term, instrumental preferences. If one party is trying to develop itself over the long term, it might run even if it knows it can't win right now.
  • Examples: Studies of Japan (LDP learned not to overnominate), Chile (Concertacion).


If parties don't regulate entry (i.e. they overnominate), then voters are likely to channel their votes primarily to the top candidates using the M+1 rule. Assumes that voters are instrumental and interested in short-term victories.


Use "I" (inflation factor--see above) to measure degree of each state's linkage. Linkage (Y) varies in response to two variables:

  • X1: Upper tiers or vote distribution requirements. Incentives for linkage are stronger if you are trying to win in an at-large district (an upper-tier) that is bigger than the rest of the districts, or if votes must be dispersed geographically for a party's presidential candidate to win.
  • X2: Centralization of power (unicameral, parliamentary, and unitary are more centralized than bicameral, presidential, and federal). When power is centralized, the incentives to coordinate are higher--since you have more to gain from doing so. (When there are more ways to get veto power--i.e. bicameral, presidential, and federal--it is less necessary to win everything nationwide in order to defend your interests.) See also Hicken 2005.

Evidence for X1 and X2:

  • India and the USA: See Chhibber and Kollman (1998), who demonstrate a correlation between level of centralization and linkage.
  • Brazil: Samuels (1998) notes as a side point that Brazil's decentralized government (lots of power for local states) prevents parties from linking together (evidence for X2).
  • Possible X3: Social cleavages. Social cleavages can prevent coordination at both (a) and (b) if they are salient enough. See Ferree (2005) and maybe Lipset and Rokkan.
  • Thailand: Institutional changes made linkage happen (Hicken 2005).