The reversal of the inequality between the ratios , which creates Simpson 's paradox , happens because two effects occur together : Based on these effects , the paradoxical result can be rephrased more intuitively as follows : Treatment A , when applied to a patient population consisting mainly of patients with large stones , is less successful than Treatment B applied to a patient population consisting mainly of patients with small stones .
The reversal of the inequality between the ratios , which creates Simpson 's paradox , happens because two effects occur together :