See this post, which I think is a low quality one but wasn't prevented from being posted.
Given that it's a question shouldn't it have at least one question mark?
So, should the quality filter take into account the lack of a question mark?
My only worry this catching people whose grammar is generally poor; but then we already do things like not liking proper casing etc.
See this query for some data, which might indicate a correlation between good questions and the presence of a question mark (I do see that the difference could be considered slight, although I've not analysed score differences for what we believe to be currently included in the filters to determine whether they are too slight or not). Also note that this would include a question mark as part of code which further muddies the water.
Count ,Sum ,FavoriteCount,AverageScore ,AverageFavoriteCount,QuestionMark 1017086,932969 , 328823 ,0.91729607919,0.32329911138 ,0 3826947,6565454,2220523 ,1.71558529553,0.58023353864 ,1
SELECT COUNT(*) AS [Count], SUM(Score) as [Sum], SUM(FavoriteCount) as FavoriteCount, CAST(SUM(Score) AS decimal) / COUNT(*) AS AverageScore, CAST(SUM(FavoriteCount) AS decimal) / COUNT(*) AS AverageFavoriteCount, CASE WHEN BODY LIKE '%?%' OR Title Like '%?%' THEN 1 ELSE 0 END AS QuestionMark FROM Posts WHERE PostTypeId = 1 GROUP BY CASE WHEN BODY LIKE '%?%' OR Title Like '%?%' THEN 1 ELSE 0 END