A surgeon performed two types of surgeries to treat large kidney stones and small kidney stones. Treatment A on large stones was successful 73% of the time, but on small stones it was successful 93% of the time. Treatment B was successful on large stones 69% of the time, but on small stones it was successful 87% of the time. The overall report stated treatment B was more successful. What may make this claim possible? A) Sampling Error B) Cause-and-effect relationship C) Convenience Error D) Confounding E) Simpson's Paradox