Well you may have not intended your site to be a acedimic resource, but it was being refered to, by someone, in an acedmic debate (of sorts), hence my objections.
Meanwhlie, I don't think cannabis is a big source of bias, mainly because there has been much more, and better studies done on cannabis and cognition, which basically show that if you've abstained for 30 days, unless you've been using for a very long time (maybe 30ish years), it doesn't have an effect. You could say that there was only an abstinance period of 6 days, but seeing as the people were clear of cannabinoids in their urine, I think they had been abstinant from cannabis for at least around 30 days.
Well if you're gonna start complaining about sampling, then you can tear any epidemiological study up. You need to have some faith, that if there is a significant effect, then so long as you take care of the obvious comorbidities, then the truth will shine through.
I think the bigger concen is that the ex-users group is obviously fucked up, judging by table 4.
But still, my point, from the begining, isn't that there is proof one way or the other, just that there is not enough research to say "it is unlikely to occur". Even if he had said "from my readings I find it unlikely to occur".