Illusory placebo effect

People didn't improve but they thought they had because of the tapes.

The illusory placebo effect refers to the phenomenon where individuals perceive an improvement in their condition due to their belief in the efficacy of a treatment, even though the treatment has no actual medical value. In this context, the "tapes" likely served as a placebo—a substance or procedure a person believes will improve their health or condition, based on their expectations rather than any physiological effect.