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160 healthy women undergoing were assisted reproductive therapy for study.

A double-blind experiment is one in which neither the subjects nor the individuals who measure know which treatment was received, while in the single-blind experiment either the individuals who measure or the subjects know which treatment was received (but not both).

A placebo is something that is identical to the treatment received by the treatment group, except that is contains no active ingredients.

The difference in the percent of women who became pregnant in the two groups is

statistically significant.

The placebo effect is an effect produced by a placebo, which cannot be due to the placebo itself, and is thus caused by the patient's belief in that treatment.

In this case, we note that the study was not blinded, because the women were aware of which treatment they received.

The design of the study prevents us from concluding that acupuncture

caused the difference in pregnancy rates.

This then prevents us from concluding causation, because the knowledge of which treatment they received could affect the results of the study and thus we cannot determine which differences are due to the placebo effect and which differences are due to the treatments themselves.