Bruce Schneier and Jameson Quinn have crunched the numbers on EPH using the 2015 nomination data and simulated data. There is an explanatory post at File770 here and also the paper is available here https://www.schneier.com/academic/paperfiles/Proportional_Voting_System.pdf
In the table: AV stands for Approval Voting (the system used at the nomination stage); SDV is Single Divisible Vote; SDV-LPE is the proposed E Pluribus Hugo proprosal; SDV-LPE-SL is a tweaked version of EPH that gives it a bit more welly.
Basic summary is that EPH does what it claims but the impact is less than people might hope. For Best Novel it does very well and in Short Story it does much less well.
However, I think it is good enough looking at those numbers. There are two prongs to responding to slates – a social response and a structural response. The structural response helps the social response. For Short Story there remains an issue of a very broad field in which people’s choices tend not to coalesce round a small number of nominees. That makes it very prone to slates.
What EPH does overall is ensure that there is at least one non-slate contender which is less than ideal but does ensure that:
- People have something good to vote for untainted by slates
- A non-slate winner is possible which eliminates the positive reward for slating
- There is a choice above No Award which means the category gets a winner and hence the negative reward for slating (i.e. griefing the awards by forcing a No Award victory) is eliminated