Very interesting paper. The categorisation of upper and lower class could be problematic however. Being a paper from the US, I presume the participants' class category corresponds to assets and income, ergo upper class being simply richer. In other countries, such as the UK, one's class has a totally different meaning.
For sure, but isn't this sort of an inherent definitional challenge in such research?
It's not a methodological issue. (The methodology itself, of course, has potential issues as well, e.g. as with the "luxury car" categorization.) It's foundational: can you really say, in a culture-independent way, that "higher socioeconomic class translates to more antisocial behavior?" Not without big caveats.
I wouldn't say it has a totally different meaning - upper class people are going to be more likely to be wealthier than the average but having lots of money doesn't make you upper class - at least in the traditional UK sense where upper class means titled aristocracy.
