Excerpt: The recent study by Argamany et al1 concluded that the incidence and hospital mortality for Clostridium difficile infection (CDI) differed between major regions of the United States and across different seasonal times of the year. However, these conclusions were not supported by the data in their study because the authors based them exclusively on statistical significance without considering the effect size of their findings. The effect sizes of region and season on CDI were very low or near zero, contradicting their conclusion, as subsequently explained.