Semi-duplicate post about UN Women's recent report on VAWG
(Violence Against Women and Girls), posted here specifically in reference to violence and games and the following quote one of the reports authors gave to Vice magazine
I asked her about the report's association of violent video games with real world violence. "We've had a professor from a university share some of the studies [related to video game violence] with us and that will be reflected in the revised research. It's a difficult area because there are certainly studies that show no link [to real world violence]. But I think on the other side of the debate there's still some question because there's no longitudinal study. This is an area where it's complicated and I think we need to rely on the psychological studies."
To date the longest single study was the recently released (2015) "Sexist games=sexist gamers? A longitudinal study on the relationship between video game use and sexist attitudes
" that gathered data over a three-year period and found, generally speaking, the attitudes individuals had were not related
to their consumption of games*; an ambiguous conclusion that only highlights just how complicated our behaviors are away from laboratory conditions.
Beyond this there is indeed little in the way of multi-year studies, largely due to the vagaries, and costs, of capturing such data for extended periods of time on either side of the argument
(as the author of the quote framed the comment). With all that said however, games as a field of study have been subject to scrutiny for the best part of 40 years
(since the early 1980's), and amongst the thousands of data-points now available nothing has turned up to prove one way or the other any meaningful connection between games and violence, or sexism as is the current topic de jour as media, 'critics' and politicians would have it. In other words; Doom did not make Columbine
("violence"), nor did GTA make Santa Barbara
* it's important to stress that whilst the study suggests attitudes may not be formed by (i.e. are related to) game consumption, it similarly does not speak to whether games and their consumption sustain predispositions one way or the other. In terms of where those originate (the predispositions individuals have), how they are formed and maintained, broader study needs to be done. But again trying to find a singular cause for these questions seem like a non-starter.
** in both Columbine (Klebold and Harris - wanted to go out with as much violence as they could) and Santa Barbara (Elliot Rodgers - was largely taking revenge for being spurned by women), games were evidenced, ostensibly by the media and politicians looking for capitol, as the cause for the acts perpetrated by the individuals involved, despite their being on, or having taken, various forms of medication to treat depression or other psychological issues.