You're totally right. But honestly, that's an information that I wrote on my handbook at class, and I really don't know from where it exactly comes. Knowing that our teacher chooses informations from scientific articles, I think that it comes from an article published in a scientific journal. Anyway, I'll try to find the same information on internet and maybe I can add a link to the post, but the truth is that every articles takes the numbers/statistics from other scientific sources so it's such a difficult task to find the main source. I totally respect people who's hardworking to give us all these beautiful informations btw, that's why I'm always trying to write sentences with my words. Thanks a lot for your comment.