I looked at these studies (not the original journal articles, but your links), and I think there are many variables in place here. There are many individual differences that people have, social contexts, the influence of others (who also have individual differences), the impact of time (historical, generational, maturational), and the interactions of these. Yes, I do think that friends or partners can have an impact, but it also depends on so many other factors, which influence each other transactionally over time, within a complex, dynamic system. I am a dorky developmental psychologist, so please excuse the rant. ;)
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