Tbh I can't find any reliable info for either number since it's just estimitation. But I did find this. [FAQs on Stuttering | Institute for Stuttering Treatment and Research (ualberta.ca)](https://www.ualberta.ca/stuttering-speech-therapy/programs-treatment/faq.html) But it can go either way I think and it depends on the region of the world. I know the group in the US says that 5% of children stutter and 1% of adults, but I'm not sure how they arrived at that number.