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Phil Those are good questions and here is my attempt to answer them. Phil Tompkins wrote: > I have a few questions about the placebo effect for those familiar > with research protocols. I don't know much about this subject, so > please pardon me if I am repeating frequently asked questions. > > 1. If patients are told in advance that they may or may not receive > the real medicine or the real surgery, doesn't this tend to undo the > placebo effect? I thought that the effect is based on the patient > believing that the treatment is the real thing. It doesn't undo the placebo effect. Believe me after you have had brain surgery (or at least thought you had brain surgery) you want desperately to believe you had "the real thing". For instance in the literature I know best- psychiatry- 30% of people taking placebo antidepressants improve. With most antidepressants about 65% of med taking group improve. I had placebo when I was in an entacapone study and I knew that pretty quickly- And I was put on active drug after the study and could immediately tell the difference. > > > 2. Why do trials continue to check for the placebo effect? Haven't > enough double-blind studies been done already to tell us what we may > expect in this regard? What more is there to learn? Or does the > effect vary depending on the treatment being tested? You answered the question yourself. Placebo effects vary by procedure, disease, and situation. For instance it can be very powerful especially if an investigator believes fervently that the treatment works. So, if the investigator knows which procedure the patient had they may unconsciously- or in some cases consciously skew the data. If the patient knows they may work harder on the evaluations. In an experiment that is double blinded neither the "rater" nor the patient knows who is in the experimental group (Real procedure, drug, etc.) and who is a control. The surgery in my case was in Tampa, the evaluators are in NYC or Chicago and in fact the PET scans were done in Vancouver. Effort is made to keep the contact between surgeon (who obviously knows who got the "real " surgery) and the evaluators to a minimum. When the data is complete the code is broken and the placebo group's results of various tests are compared statistically to the experimental group(s). This comparison also needs to be done (but not necessarily blinded) to account for disease progression. If a score improves slightly in the experimental group but worsens substantially in the placebo group- that can be quite significant. I hope I have answered your questions and not added to the confusion. Charlie Phil Tompkins > Hoboken NJ > age 61/dx 1990 -- ****************************************************************************************** Charles T. Meyer, M.D. Middleton (Madison), Wisconsin [log in to unmask] ******************************************************************************************