Your reference to "editorials" didn't hit me until several days after reading your post. I have meant to get back to you on this point but have been distracted by other "issues". First of all, what 12 year period of time are you looking at. Was this a period of time in which you believe the newspapers were pretty much reporting straight news and leaving their opinions/advocacy on the editorial pages? IOW, could the news pages be trusted to have very little in the way of "advocacy" journalism??? I suppose what I'm trying to determine is will looking at just the editorials during this period of time develop the clues you seek?
FGS
Our sample is 12 years, 1958-1970; LA Times, WaPo, NY Times, Atlanta Constitution, and Cleveland Plain Dealer. It's gonna be a baseball bat between the eyes of the MSM.