Statistics and stuff.
“The first written mention of a controlled trial can be found as early as the 7th century BC in the Book of Daniel 1:11-16. The eponymous prophet asks the steward of Nebuchadnezzar, the king of Babylon, for permission to eat a vegetarian diet instead of the king’s rich and possibly non-kosher food. The king’s steward worries that Daniel and his companions will waste away, but agrees to let them test the diet for 10 days, after which adherents of both diets will be evaluated by how “fair and fat” they looked. The vegetarians win, and the steward is convinced.”
https://asteriskmag.com/issues/14/in-praise-of-observational-evidence