Passage Summary: Patients in a new type of therapy got better than those in old-school therapy, so the new therapists must be better at their jobs.

Conclusion: Therapists who use the new experimental method are more effective than those who use traditional methods.

Reasoning: A study showed that patients referred to the experimental therapists showed more improvement than those referred to traditional therapists.

Analysis: This argument suffers from a classic correlation-causation error mixed with a potential sampling bias. It assumes the therapy type is the only variable, ignoring why patients were 'referred' to one group or the other in the first place. If the doctors sent the 'easier' cases to the experimental group, the therapists' skill might have nothing to do with the better results. You should look for an answer that identifies this failure to consider alternative explanations for the patients' progress.