[stylin19a]

But researchers have not been able to establish a cause-and-effect relationship.

blind men describing an elephant.

[TigersEye]

But researchers have not been able to establish a cause-and-effect relationship.

In spite of the fact that the same phenomena happens in state after state, at different times of enactment, and no other significant changes in public policy, law enforcement policy or societal mindset can be cited as possible factors.

I think the meaning of 'cause and effect' is something they don't really understand.