The term "standard of living" is a pretty fuzzy one. The only way it makes sense is to talk about the minimum standard of living, e.g. say what the standard is for the bottom 20% of income. In this case it's probably not a good indicator for the US. The US is so diverse that "average" standard of living doesn't really mean anything. For a single (rich) state it might, as it does for a small nordic state.