Investigation pair to clearance

Can someone tell me how investigations are matched with clearances? What I am looking for is for each clearance level what type of investigation is required?

There are many articles on this blog site that would answer your questions, go forth and seek them out. Here is a start:

Thanks for the links, but can someone tell me what the new TIER investigations replace as in a one on one basis. I remember the days of NAC’s, SBI, SBBI and etc, but having a problem matching this up with the new Tier system.