"Of the 63 studies in the review, 46 were cross-sectional, meaning they measured cannabis use and violence at one point in time. This makes it difficult to tell whether cannabis use came before the violence, followed it, or simply occurred alongside other circumstances that contributed to it. These studies found the strongest link between cannabis use and violence.

Studies that follow people over time – called longitudinal studies – can help establish which came first. These studies found a much weaker link between cannabis use and violence than the cross-sectional studies."

Rest of the article goes on, but this is about the quality of research I'd expect from a Catholic associate college to a conservative university. Wonder what motivated this review.