I would counter that:That's not what the studies conclude at all. Rather, they find that previous studies have failed to establish the correlation/causation -- that's a far cry from concluding that the correlation/causation does not exist.
If since the 1968 GCA no study has found any correlation nor any causation between gun control and a reduction of crime then it is a pretty good bet that gun control doesn't impact crime.
Considering the effort put into proving that gun control works by the antis if in the 37 years since the 68 GCA not one single study can show GC helps then it probably doesn't.
By the way correlation and causation aren't even close to being the same thing.
There's a very high correlation between the phases of the moon and the homicide rate as well as the automobile accident rate but the phases of the moon absolutely do not cause high accident and homicide rates.
High correlation does not prove causation.