The sequence symmetry analysis (SSA) 1 is a self-controlled design that is being increasingly used for evaluating a large number of drug-outcome pairs. 2-4 One of the main advantages of the SSA is that it is computationally efficient compared to traditional between-person comparison designs. The measure of association obtained from a SSA is the sequence ratio (SR), which is calculated as the number of sequences where the exposure of interest occurred before the outcome of interest divided by the number of reverse sequences. Apart from the SR, one can also calculate a risk measure that loosely corresponds to the number of attributable cases in the population, which is the difference between the number of exposure-first sequences and the number of exposure-last sequences. 5 Jesper Hallas