As pain is aubjective. The subject believing their pain to be improved is an effect.

For a lot of medical science now, we look not only at medical outcomes but patient perceived outcomes.

Scientists are great at quantifying outcomes and risk evaluation mathematically. People are bad at using that data to decide on treatment, so depend on healthcare professionals to guide them. The communication skills of the healthcare provider are just as important as their clinical skill in many cases. In some cases, even more so.

If someone is happier with their objectively worse outcome, which is the better outcome?