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Ashkenazi Jews is too large a category. Try Ashkenazi Jews from a region where Tay Sachs is common for all the grandparents.
I don’t think this is possible.
Tay-Sachs allele used to slightly increase evolutionary fitness in heterozygotes (i.e. people who carry just one Tay-Sachs allele). This allowed the allele to increase in frequency until ~3% of Ashkenazis became its carriers. But once the local frequency becomes high enough the negative effects (the risk that a random couple produces children with two Tay-Sachs alleles) balance the positive effects on fitness. Thus in any region it should be impossible for Tay-Sachs to be common for all the grandparents.
Why wouldn't having grandparents from different continents make rare alleles less likely to be reinforced?
There is some reinforcement, but it’s not very significant.
For example, consider an Ashkenazi Tay-Sachs carrier who marries a person from China. If their children mate, the chance that the grandchildren would have Tay-Sachs disease is (1/2)^4=1/16. If instead of a Chinese, this Ashkenazi Tay-Sachs carrier marries another Ashkenazi (who have ~0.03 chance of being a carrier), the chance that the grandchildren would have Tay-Sachs disease is almost the same, ~1/16*1.12. In absence of incest, a grandchild of a Tay-Sachs carrier would have a ~0.03/8 (i.e. ~17 times smaller) chance for getting the disease.
From what I've heard, the genetic risks have a lot to do with how genetically similar the forebears of the couple are. If all the grandparents are from the same small region, it's a lot riskier than if the grandparents are from different continents.
I don’t understand why the origin of grandparents should matter.
To the best of my knowledge, the main problem with incest is recessive alleles. For example, if the grandfather’s genotype is ”aA” (where “a” is a very rare recessive allele) and his children (parents’ generation) mate with each other, then there is a relatively high chance (1/16) that the grandchildren would be of “aa” genotype (which might be extremely deleterious or even lethal). Having another grandparent from a different continent should not change this.
Any particular reason you did a plot this way instead of having a cloud of points and drawing some kind of regression line or curve through? You are unnecessarily losing information by aggregating into buckets.
True, but it is virtually impossible to see a meaningful pattern when you have thousands data points on the graph and R2<0.2.
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You seem to be assuming commenters either agree or disagree with a post. But usually there are more than just two opposite or pro/con positions, and many more things to say on a subject than "yes" or "no". Many posts aren't arguing for or against something to begin with, they're describing, reporting, or asking something.
Also, did you use the total number of comments on a post, or just the top-level comments? The former would count many extended discussions that often have little to do with the OP.
Is there a reason to think that the number of extended discussions that have little to do with the OP is higher for articles with negative karma? If not, counting the total number or just the top-level comments should not affect the conclusions.
Solving the problem for a simple binary case is a starting point in our tests.