Let's see.
One study, although published in a reputable journal, isn't enough to sway my opinion on anything. That being said, this study seems well-done.
However, this study is reporting correlative predictions only, and does not imply causation. There are a few quotes I wish to highlight:
This study found that watching television, videos or DVDs for 3 h or more daily was associated with a small increase in conduct problems between the ages of 5 years and 7 years, after allowing for
other child and family characteristics, including parenting. Findings are in line with other research on younger children aged 2–4 years and older children showing associations between TV exposure and aggressive behaviour and bullying[…].
So, watching more TV is correlated with more behavioural problems.
We did not find associations between electronic games use and conduct problems, which could
reflect the lower exposure to games and/or greater parental restrictions on age-appropriate content for games compared with TV.
This is one of the more important quotes. The news article Natsuru linked completely glossed over the huge qualifying statement here. So, don't take the news article at face value. And what's more, this statement pertains only to conduct problems, not any other behavioural or mental issues.
The study highlights the need for more detailed data to explore risks of various forms of screen time, including exposure to screen violence.
A good study will always discuss its limitations, as this one did. The authors readily admit that more information is needed on specific types of TV and games. For example, if a kid watches 5 hours of Sesame Street, it would probably have a different effect than watching 5 hours of Breaking Bad. The same with games; spending 5 hours playing DOOM is surely different than spending 5 hours playing Animal Crossing.
However, the study suggests that a cautionary approach to the heavy use of screen entertainment in young children is justifiable in terms of potential effects on mental wellbeing, particularly conduct problems, in addition to effects on physical health and academic progress shown elsewhere.
And here you have it. Despite not finding correlations between conduct issues and game exposure, the authors are advocating that excessive TV and game exposure, in general, is likely harmful to children. Again, the news article seems to have skipped this completely.
So once again, the media picks up on a scientific study and completely misinterprets the results. Absolutely typical – this is why you should always read the scientific papers and not just the news.
Oh yeah, and Nats' post is, well, pretty much all wrong (except for the last bit).