Using the distribution of observed % RH (Figure ), "low" and "high" humidity conditions were defined as the bottom (18.3 -44.9% RH) and the top (54.7 -63.0% RH) terciles, respectively. As the polymer-capacitive humidity sensors have a ±2.5% precision, 27 restricting attention to the top and bottom terciles focuses on the cases where the effect is largest. Five organoammonium iodide salts had batches conducted in both low and high humidity conditions; the observed crystallization probability for the low and high humidity batch of experiments are depicted on the horizontal and vertical axes of Figure for each species. As experiments in each batch are independent, the probability that both events occur is the product, and the probability of more successes in a than in b is