I was also curious about the population of participants. The paper has this to say: > The test was made available on a dedicated website (http://vocabulary.uge

I was also curious about the population of participants. The paper has this to say: > The test was made available on a dedicated website (http://vocabulary.ugent.be/ http://vocabulary.ugent.be/). Access to the test was unlimited. > we analyzed the data of 221,268 individuals who completed 265,346 sessions. That's a pretty large sample, although I wonder how they recruited the participants. It may be in the paper but I couldn't find mention of that in a quick skim.