i'll call n the total number of patients. if n * 9 / 1000 = 13, you'll find out that n is around 1400, which is a pretty high number in discovery studies. Maybe not for diabetes though, i remember hosting anonymized data from a lot more patients two years ago, i felt this was THE subject all the medical founding was put into (that and air quality and its effect studies).
Also not adjusting for confounders is statistically ridiculous. As well as n=13 studies.