I've been working on extending Stephanopoulos-McGhee's definition of the efficiency gap using the method outlined in following Stack Exchange post.
It seems that extending the definition of wasted votes in this manner to compute pairwise efficiency gaps results in some problems, particularly when dealing with smaller parties (which receive a smaller number of total votes and thus a smaller number of wasted votes).
This problem means that the 8% threshold recommended by Stephanopoulos-McGhee will always almost be exceeded in the case where comparatively small parties run for election (the resulting efficiency gap will usually indicate gerrymandering in favour of the smaller party by these standards).
In order to deal with this problem, a new threshold appears to be needed in the multiple party case, however, I am struggling to work out what this threshold might need to be.
Does anybody have any ideas of how to deal with this?