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The efficiency gap is calculated by taking the number of net wasted votes and dividing it by the number of total votes. Every vote for a losing party in a distr

The efficiency gap is calculated by taking the number of net wasted votes and dividing it by the number of total votes. Every vote for a losing party in a district is wasted, as is every vote for the winning party over 50% + 1. This metric was very convincing to me until I noticed one thing: if a district election is split 75%-25%, then it seems that the net wasted votes is 0. But a state where every district is split 75-25 is clearly heavily gerrymandered! Am I missing something?

smeyer 9y ago
I don't think you're understanding the calculation correctly. If a district election is 75-25, then the wasted votes is 24 (75 minus the 51 required to win). I believe the computation of net wasted votes comes from looking across several districts. Here's an example from another article: >Suppose, for example, that a state has five districts with 100 voters each, and two parties, Party A and Party B. Suppose also that Party A wins four of the seats 53 to 47, and Party B wins one of them 85 to 15. Then in each of the four seats that Party A wins, it has 2 surplus votes (53 minus the 51 needed to win), and Party B has 47 lost votes. And in the lone district that Party A loses, it has 15 lost votes, and Party B has 34 surplus votes (85 minus the 51 needed to win). In sum, Party A wastes 23 votes and Party B wastes 222 votes. Subtracting one figure from the other and dividing by the 500 votes cast produces an efficiency gap of 40 percent in Party A’s favor. https://newrepublic.com/article/118534/gerrymandering-efficiency-gap-better-way-measure-gerrymandering https://newrepublic.com/article/118534/gerrymandering-effici...
- snarf21 9y ago
  He is saying, if you could gerrymanderer every district at 75-25 the gap would be 0 even though it would be likely that couldn't happen without being heavily gerrymandered. I think all districts being 75-25 is not really possible based on how communities grow and group together socially and economically.
  - smeyer 9y ago
    But if every district is 75-25, neither party is gaining a net advantage. If you have 10 districts and split them into 5 that are 51-49 and 5 that are 49-51 or if you split them into 5 that are 75-25 and 5 that are 25-75, you have 5 representatives from each party either way. The point of the gap is to distinguish between cases like this (where districts are designed to lump together people of a similar part) from examples of packing and cracking used to give one party an advantage.
    - dragonwriter 9y ago
      > But if every district is 75-25, neither party is gaining a net advantage. Partisan advantage is far from the only reason for gerrymandering; protecting incumbents and dividing particular communities of interest (whether ethnic or otherwise) that don't necessarily align more with either party to effectively silence them are among two of the more common uses. A recent wave of extreme partisan gerrymandering by Republicans is what has made it a national discussion right now, but it's not the only (or even historically the main) problem with gerrymandering. Which is simple to solve: stop having single-member, first-past-the-post districts for legislative bodies.
    - phailhaus 9y ago
      If every district is 75-25, then the issue is that one party is getting 25% of the votes but 0% of the seats. All of their votes have been split across all districts, keeping them from winning any one.
      - mjw1007 9y ago
        One way for that to happen is if party support is evenly spread throughout the region; then however you draw the districts the result will be the same. In that sort of situation it doesn't seem to be reasonable to call what's going on "gerrymandering"; I think the finger of blame should be pointed (if anywhere) at the system of single-member-constituency plurality voting.
        9y ago
snarf21 9y ago
What you are saying is true. However, it is probably hard to find a real example of being to divide a state (e.g.) into X groups that all have that 75-25 mix. Normally, the city vs country or ethnic groupings will leave certain areas in opposite mixes. The gerrymandering that usually happens is that the group in charge wants to win 3/4 of the X seats at a small percentage like 60-40 and lose 1/4 of the X seats by a huge margin like 90-10. This would give them a huge seat advantage since they own most of the seats. In this case, the gap would be huge proving deliberate gerrymandering.
- phailhaus 9y ago
  It doesn't matter if it's unlikely, the point is that the efficiency gap is being proposed as a measure of partisan gerrymandering, but it clearly does not do what it claims because it thinks a state with all districts split 75-25 is fair. But it's not: one party is getting 25% of the votes but 0% of the seats.
  - snarf21 9y ago
    I'm agreeing with you that a case like this isn't being fairly measured by this gap. I'm not trolling but the likeliness does play into it. This case is not much of a concern if it has never happened in any state in US history, e.g. I think there are other things that can be done to make it even harder to create all 75-25 like saying all districts must have a size or density or .... that is within a standard deviation (or two?) of the mean. I don't know what the right math is offhand but something like this adds another constraint.
    - phailhaus 9y ago
      My point is that there's clearly something missing if a 75-25 split is measured as 0 net wasted votes. That means that the efficiency gap treats 75-25 as the "perfect election", and is actually measuring how far any given district election is from that "ideal". Even worse, that means that if we actually use the efficiency gap to measure gerrymandering, then there is a strong incentive for parties to draw district lines to be as close to 75-25 as possible!
mjw1007 9y ago
Consider a state with twelve districts: six 75-25 A-B, six 75-25 B-A. Votes are even, seats are even; the state isn't gerrymandered. So it isn't the case that a state where every district is split 75-25 is necessarily heavily gerrymandered. On the other hand, if all twelve districts are 75-25 A-B then it seems like B has three fewer seats than it deserves, which does suggest that that definition of an efficiency gap is missing something.
- phailhaus 9y ago
  Yeah, it seems like the metric can't tell the difference between the two situations...
a_t48 9y ago
Also interested to hear.
deleted 9y ago
[deleted]
maxerickson 9y ago
It's not a district level measure. It is a measure of how a district plan affects the statewide outcome. The worked example in the definition section of the paper lays it out pretty clearly: http://chicagounbound.uchicago.edu/cgi/viewcontent.cgi?article=1946&context=public_law_and_legal_theory http://chicagounbound.uchicago.edu/cgi/viewcontent.cgi?artic... If you take 3 districts, with 2 going to A and 1 going to B, 300 votes at 75-25 would be split into 175 and 125. That's a reasonable outcome, the majority took 2 seats, the minority gets approximately proportional representation. Compare to 300 votes going 51-49 (the most extreme efficiency gap). The ~1/2 minority gets 0 representation (153 vs 147 for that election).

smeyer 9y ago

I don't think you're understanding the calculation correctly. If a district election is 75-25, then the wasted votes is 24 (75 minus the 51 required to win). I believe the computation of net wasted votes comes from looking across several districts. Here's an example from another article: >Suppose, for example, that a state has five districts with 100 voters each, and two parties, Party A and Party B. Suppose also that Party A wins four of the seats 53 to 47, and Party B wins one of them 85 to 15. Then in each of the four seats that Party A wins, it has 2 surplus votes (53 minus the 51 needed to win), and Party B has 47 lost votes. And in the lone district that Party A loses, it has 15 lost votes, and Party B has 34 surplus votes (85 minus the 51 needed to win). In sum, Party A wastes 23 votes and Party B wastes 222 votes. Subtracting one figure from the other and dividing by the 500 votes cast produces an efficiency gap of 40 percent in Party A’s favor. https://newrepublic.com/article/118534/gerrymandering-efficiency-gap-better-way-measure-gerrymandering https://newrepublic.com/article/118534/gerrymandering-effici...

snarf21 9y ago
He is saying, if you could gerrymanderer every district at 75-25 the gap would be 0 even though it would be likely that couldn't happen without being heavily gerrymandered. I think all districts being 75-25 is not really possible based on how communities grow and group together socially and economically.
- smeyer 9y ago
  But if every district is 75-25, neither party is gaining a net advantage. If you have 10 districts and split them into 5 that are 51-49 and 5 that are 49-51 or if you split them into 5 that are 75-25 and 5 that are 25-75, you have 5 representatives from each party either way. The point of the gap is to distinguish between cases like this (where districts are designed to lump together people of a similar part) from examples of packing and cracking used to give one party an advantage.
  - dragonwriter 9y ago
    > But if every district is 75-25, neither party is gaining a net advantage. Partisan advantage is far from the only reason for gerrymandering; protecting incumbents and dividing particular communities of interest (whether ethnic or otherwise) that don't necessarily align more with either party to effectively silence them are among two of the more common uses. A recent wave of extreme partisan gerrymandering by Republicans is what has made it a national discussion right now, but it's not the only (or even historically the main) problem with gerrymandering. Which is simple to solve: stop having single-member, first-past-the-post districts for legislative bodies.
  - phailhaus 9y ago
    If every district is 75-25, then the issue is that one party is getting 25% of the votes but 0% of the seats. All of their votes have been split across all districts, keeping them from winning any one.
    - mjw1007 9y ago
      One way for that to happen is if party support is evenly spread throughout the region; then however you draw the districts the result will be the same. In that sort of situation it doesn't seem to be reasonable to call what's going on "gerrymandering"; I think the finger of blame should be pointed (if anywhere) at the system of single-member-constituency plurality voting.
      - 9y ago

snarf21 9y ago

What you are saying is true. However, it is probably hard to find a real example of being to divide a state (e.g.) into X groups that all have that 75-25 mix. Normally, the city vs country or ethnic groupings will leave certain areas in opposite mixes. The gerrymandering that usually happens is that the group in charge wants to win 3/4 of the X seats at a small percentage like 60-40 and lose 1/4 of the X seats by a huge margin like 90-10. This would give them a huge seat advantage since they own most of the seats. In this case, the gap would be huge proving deliberate gerrymandering.

phailhaus 9y ago
It doesn't matter if it's unlikely, the point is that the efficiency gap is being proposed as a measure of partisan gerrymandering, but it clearly does not do what it claims because it thinks a state with all districts split 75-25 is fair. But it's not: one party is getting 25% of the votes but 0% of the seats.
- snarf21 9y ago
  I'm agreeing with you that a case like this isn't being fairly measured by this gap. I'm not trolling but the likeliness does play into it. This case is not much of a concern if it has never happened in any state in US history, e.g. I think there are other things that can be done to make it even harder to create all 75-25 like saying all districts must have a size or density or .... that is within a standard deviation (or two?) of the mean. I don't know what the right math is offhand but something like this adds another constraint.
  - phailhaus 9y ago
    My point is that there's clearly something missing if a 75-25 split is measured as 0 net wasted votes. That means that the efficiency gap treats 75-25 as the "perfect election", and is actually measuring how far any given district election is from that "ideal". Even worse, that means that if we actually use the efficiency gap to measure gerrymandering, then there is a strong incentive for parties to draw district lines to be as close to 75-25 as possible!

mjw1007 9y ago

Consider a state with twelve districts: six 75-25 A-B, six 75-25 B-A. Votes are even, seats are even; the state isn't gerrymandered. So it isn't the case that a state where every district is split 75-25 is necessarily heavily gerrymandered. On the other hand, if all twelve districts are 75-25 A-B then it seems like B has three fewer seats than it deserves, which does suggest that that definition of an efficiency gap is missing something.

phailhaus 9y ago
Yeah, it seems like the metric can't tell the difference between the two situations...

a_t48 9y ago

Also interested to hear.

deleted 9y ago

[deleted]

maxerickson 9y ago

It's not a district level measure. It is a measure of how a district plan affects the statewide outcome. The worked example in the definition section of the paper lays it out pretty clearly: http://chicagounbound.uchicago.edu/cgi/viewcontent.cgi?article=1946&context=public_law_and_legal_theory http://chicagounbound.uchicago.edu/cgi/viewcontent.cgi?artic... If you take 3 districts, with 2 going to A and 1 going to B, 300 votes at 75-25 would be split into 175 and 125. That's a reasonable outcome, the majority took 2 seats, the minority gets approximately proportional representation. Compare to 300 votes going 51-49 (the most extreme efficiency gap). The ~1/2 minority gets 0 representation (153 vs 147 for that election).