Please ignore this "study" and whatever Jaroslav Flegr says. At my university he was mocked for his misuse of statistics - he does it even in this article, giant models with huge sample sizes finding correlations everywhere with p < 0.1.<p>Also, in this article <a href="https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-015-1290-7" rel="nofollow">https://parasitesandvectors.biomedcentral.com/articles/10.11...</a> he says that "pathogen responsible for mood disorders in animals-injured subjects is probably not the protozoon Toxoplasma gondii but another organism; possibly the agent of cat-scratched disease – the bacteria Bartonella henselae."
So did he discover yet another behaviour change inducing organism, or is he simply a shitty scientist? Let's have a look: he recruits respondents via Facebook, they take 4 psychological questionnaires (which are usually not very reliable and shouldn't be used in giant correlation tables) and finds effect sizes ranging from eta2 = 0.004 to eta2 = 0.045. Just look at this table - <a href="https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-015-1290-7/figures/1" rel="nofollow">https://parasitesandvectors.biomedcentral.com/articles/10.11...</a> - results are significant because the sample size is 5000, but what are the practical differences? Barely 1 point on a scale that itself has reliability around 0.9 (which is good, but it still leads to standard measurement error greater than Flegr's effect sizes).