The certainty bump is a function of a variety of different aspects of the lack of response, including the fact that he didn't even say something like what you suggest about ""Interesting. Why do you believe that? And that he's not responded even as this thread has grown, and he didn't respond to either PMs (apparently) or the first public call out.
There's also an aspect of personalities that is relevant here. Frankly, I'd expect you to say something like your suggested response whether or not you were actually engaging in the behavior in question. If Eugine were not, given the rest of what I've seen of his interaction, I'd expect that he'd be substantially more likely to vocally deny it, since he's generally blunt. And the 10% to to 50% has included finding out related information such as the fact that twice before ialdabaoth made direct comments to Eugine about this that got no response at all. See here and here.
So I should clarify that the movement from 10% to 50% is not just Eugine's lack of denial, but the complete lack of response and finding out that this isn't a new thing at all but something that has happened repeatedly previously.
(nods) OK. Thanks for clarifying.
Frankly, I'd expect you to say something like your suggested response whether or not you were actually engaging in the behavior in question.
Yup, I'd expect that as well.
I'm just tired of the signal pollution, and would like to be able to use karma to honestly appraise the worth of my articles and posts, without seeing 80% of my downvotes come in chunks that correspond precisely to how many posts I've made since the last massive downvote spree.
EDIT to add data points:
Spurious downvoting stopped soon after I named a particular individual (not ALL downvoting stopped, but the downvotes I got all seemed on-the-level.)
One block of potentially spurious downvoting occurred approximately one week ago, but then karma patterns returned to expected levels. I consider this block dubious, because it reasonably matches what I'd expect to see if someone noticed several of my posts together and disagreed with all of them, and did not match the usual pattern of starting with the earliest or latest post that I had made and downvoting everything (it downvoted all posts in a few threads, but not in other threads), so I'm just adding for completeness.
Spurious, indiscriminate downvoting started up again approximately half an hour ago on Sunday (12/1/2013), around noon MDT.
Edit: And now on Tuesday, 12/3/2013, at 10 AM, I'm watching my karma go down again... about 30 points so far.
Edit: And now on Saturday, 12/14/2013, at 2 PM, I'm watching my karma go down again... about 15 points so far, at a rate of about 1-2 points per second.