Four patients from the simulated trial were measured repeatedly over time using the Positive and Negative Syndrome Scale (PANSS). A, The differences in a patient’s symptom severity scores from time point to time point are independent of any intervention. B, Measuring repeatedly and calculating the means over all time points account for random within-patient fluctuations and reveal that patients had the same mean PANSS score. What differed was the amount of random fluctuation, which might be a highly unlikely scenario but, until tested, cannot be assumed is not true.