[naturalgradient]

I would disagree with 3 because there are many in 2 and 3 which can go to 1 just by losing their job and e.g. having one high medical bill (in the states at least).

So surely there must be differentiation on whether any given job or emergency can affect your standard of living significantly.

[organsnyder]

I'd say one of the differences between 2 and 3 is that people in category 3 are virtually immune to dropping a level due to life events.

[ck425]

Medical bills aside (the US system is batshit!!) good financial planning should make going from 2 and 3 to 1 far less likely. Unfortunately many people don't bother to save significant backup funds while things are going well.

[dsnuh]

There's also divorce. Trust me, it can drop you down to 1 in a heartbeat.

[Rotdhizon]

I'd say look at this generically, without adding exceptions for outliers. Even for #3, a multi-million dollar medical bill could be a huge setback. I'm talking more along the lines of standard happenings. Say if a kid gets sick and the parents need to fork out a few hundred/thousand dollars for treatment. #2 would be able to rely on their cushion to avoid being cast down into #1.