How do governments set up any policies about nutrition?

[mm~~Ed~~mm]

Well...I was confused when I studied nutrition at school recently. According to the textbook, we know that " DRIs (Dietary Reference Intakes) " contains four Indexes , which are AI (Adequate Intakes) , EAR ( Estimated Average Requirement), UL (Tolerable Upper Intake Levels) and RDA (Recommended Dietary Allowance). Among the above-mentioned factors, which one could be the most effective information resource for the government to set up some nutritional polices? Is it "AI" or "EAR"? I am quite in a hurry looking for an answer ,and hope that someone majoring in nutrition can help me with this problem! Thanks a lot!!!