Such a study is inherently observational and very well might be looking at a confounder. Do people who X do better at Y? Or do people who *can* do X do better

Such a study is inherently observational and very well might be looking at a confounder. Do people who X do better at Y? Or do people who *can* do X do better at Y? Are married people happier, or are some people who were dealt bad hands in life both unhappy and unable to find someone that would marry them? An awful lot of longevity-related stuff appears to be of this sort.