When I was with IBM back in the day, there was one "systematic" process for RAs, but with ample room for variations. Simply put, upper management within a division would set an overall goal like "cut 10% of employee cost". Then various rules and dictates would come down from HR and legal as to how the cuts would proceed. This would ensure that business results were achieved in a consistent manner and not leave the company open to legal action. This would also account for individual employee differences that would result in different RA treatments (contractual agreements, payment of bonuses, stuff like that).
FYI...in every RA situation I saw at the company, the actual cut list came from a second-line manager or above, again based on dictates from HR and legal. I never saw a first line manager who chose to RA someone in their own department...problem employees would be fired before they were RA'd, and poorly-rated employees would end up on the cut list via dictates from HR.
I read it at @djc+1m5fLwq7.