[bumby]

>My point is that the respondents may have been a self-selecting group due to a third factor

The article addresses this:

"It is possible that those individuals classified as Dependent experienced an exaggerated set of negative consequences related to their Internet use compelling them to respond to advertisements for this study."

You seem to be losing focus on what the article is about, namely non-intoxicant addiction. "addiction can be defined as an impulse-control disorder which does not involve an intoxicant." If you were talking about a sexual addiction rather than a sexual preference, it would be an apt analogy.

To your point, yes, the context of impairment is being adaptive to the society in which one lives. The hermit living off the grid in Montana would probably be classified as maladaptive to modern society even if they think that society exhibits negative traits. That is a distinctly different claim as to whether that modern society exhibits certain favorable characteristics. This study was about the former point and made no claims to the latter.

The respondents characterized the Internet addiction as akin to cigarette cravings. I think it's possible (or even likely) there are confounding factors that drive this, but I think this study was asking a much simpler question of "Does Internet use display negative behavioral manifestations that align with other non-substance addictions, like gambling." To that point, either of those (Internet use or gambling) could be driven by societal factors.