[sdoering]

In studies like these you can only look for correlation, not causation. But you can look for other factors, so to eliminate some theories.

here for example the socialization-hypothesis. So it seems, that they have found a way to debunk the theory, that more violent teens tend to play more violent videogames. they controlled for pre-playing aggression-levels, and they monitored the developement of aggression over a longer period of time, to see, if the level of aggression changed (as it seems to do), when playing violent games.

So yes, the can only show a more or less strong correlation between these two factors (and there might be a lot of other factors not controlled for), but they can show, that some other hypothesis does not explain the data.

not more - but not less either.

[pygy_]

In this case, the temporal sequence suggests a causation.

A non-causal association would have to be induced by a confounding factor that first causes teens to play violent video games then to behave aggressively, but never in the other order.

The causal effect is reinforced by the dose effect in the context of this temporal sequence, i.e. the more hours they play per day, the more likely they are to behave aggressively.

[gojomo]

A non-causal association would have to be induced by a confounding factor that first causes teens to play violent video games then to behave aggressively, but never in the other order.

Yes, but not "never in the other order": just more often/strongly in the games-first order.

And I don't find such confounding factors hard to think up for 9th-12th graders: difficult family life; social problems with peers; substance abuse; academic performance pressures; etc.

If a teen were to react to any of these, first, by escaping into violent video games (as a relatively easy temporary mood boost), but then second, with measurable aggression, it would fit the sequential relation seen. But we wouldn't know with any sort of confidence if the violent-gameplaying interim behavior worsened or lessened the eventual aggression.