Figure 2.

Illustrative case-crossover study of the effect of cannabis use on injury, demonstrating time-varying confounding. Figure shows timelines for six individuals (A to F); different to those individuals A to F in figure 1. All individuals had an injury (crossed red circles). Cannabis use (occurring at the left edge of the purple rectangles) and alcohol consumption (left edge of orange rectangles) in the hour before death are compared with the same period 24 hours before death (empty red circles). In this example, co-occurrence of cannabis and alcohol consumption would result in the association between cannabis use and injury being confounded by alcohol use