In reply to Philip:
> The questions (sort of) make sense, but the interpretation doesn't. They're not so much "classes" as social groupings that will vary with time.
Yes, agree. The most obvious one is that quite a high proportion of people in their generally middle-class groupings are going to move category over time as they get more senior and better paid jobs, move from renting to owning a house, put a bit of money aside etc. You wouldn't call this class mobility in a conventional sense, more variation with age within a class. The fact that the classes have different average ages underlines this.
I'd have thought that they could have worked around this by controlling for age in some manner, although I'm not sure how easy it'd be...