One would assume that the reader of such a study would already know the flaw of correlation vs causation. It is taught when we learn how to interpret the results of experiments.

This study however does not stand by itself. There will be more, if there aren't already, and all they are doing is backing up the conventional wisdom about the effects of marijuana.

It definitely makes you forget. I grew up with two parents who smoked it, DAILY. They remembered nothing. Seriously.