I have been invoked by Heinrich Müller, and I corroborate him. Sociolinguistics, after all, is sociology.
The classic study of formality and social level is Labov’s “4th floor” study, in 1966 New York. Or should I say, New Yawk.
Labov walked into Saks (upper class), Macy’s (middle class) and Klein’s (lower class), and asked for directions to something that was on the fourth floor. Which, in lower class New Yorkese, was fawth flaw. And in upper class New Yorkese, was fourth floor.
The shop assistants in Saks said fourth floor the most. That doesn’t mean they were upper class, but that they were the most compliant to class practice.
But the most anxiety about saying fourth floor was at Macy’s. When you said “pardon?” there, they would immediately rush to correct their fawth to fourth. And they overused (hypercorrected) their r’s the most.
The middle class are socially mobile—or at least, they like to think they are. Studies have repeatedly confirmed that have the most anxiety about sounding formal, which often extends to hypercorrection. They have something to prove; those who have already arrived, don’t. And of course, these are not just sociolinguistic phenomena, they extend to the behaviour of the social mobile in general.
For which, see illustration in Keeping Up Appearances. Or in the contrast between, say, the Real Housewives of Orange County and the Real Housewives of Beverly Hills.