I want to know the answer to the following question:
What did the studies regarding the effectiveness of hypnosis lack?
All the background I'm provided with is that "A 2007 review of 13 studies found evidence for the efficacy of hypnosis in the reduction of chronic pain in some conditions, though the number of patients enrolled in the studies was low, bringing up issues of power to detect group differences, and most lacked credible controls for placebo and/or expectation.". Is that enough to answer the question?
Answer: yes