critically evaluate existing research on videogames, aggresion and
violent behaviour, are they effective in the debate about video games
and violence?

$2?

perhaps you should do your own homework.

here is a list of web sites
http://newsnet.byu.edu/story.cfm/43928
http://web.ics.purdue.edu/~sherryj/videogames/papers.htm
http://faculty.washington.edu/pbell/kidtech/archives/00000136.htm
http://www.psu.edu/dept/medialab/research/vgviolence.html
http://www.mediascope.org/pubs/ibriefs/vgv.htm
http://www.mediascope.org/pubs/ibriefs/vgv.htm