Edited sentence: Consequently there has been a call to increase qualitative research studies that can better examine the whole chiropractic clinical encounter.However, chiropractic treatment involves a manipulation; "sham" procedures cannot be easily devised for this, and even if the patient is unaware whether the treatment is a real or sham procedure, the doctor cannot be unaware.It is also a problem in evaluating treatments; even when there are objective outcome measures, the placebo effect can be very substantial.Similarly, it is often difficult to devise a sham procedure for surgical procedures, but it is not impossible.These are designed so that neither the patient nor the doctor knows whether they are using the actual treatment or a placebo (or "sham") treatment.Thus there may be "observer bias" - the tendency to see what you expect to see, and the potential for the patient to wish to report benefits to "please" the doctor.Thus, DCs have historically relied mostly on their own clinical experience and the shared experience of their colleagues, as reported in case studies, to direct their treatment methods.When testing the efficacy of health treatments, double blind studies are considered acceptable scientific rigor