Categories of scientific evidence- revisited

Categories of Scientific evidence In an earlier Blog I referred to Roy Walfords 4 categories of scientific evidence: >Testimonial, argumentative, correlative and the gold standard double blind model. It is only in the last category (double blind procedure) that the researcher don't know who are receiving the drug or procedure and those just receiving a placebo. In my view the researcher may also be blind to many other physiological and/or biochemical qualities of their patients like the nutritional status, the microbiological flora of their intestines or the lungs which are exposed directly to the external environment Recently nutritionists have shown that levels of Vit D play an important role not only in osteoporosis but also in Alzheimer's and even autism.We also rarely compare and/or know the status of patients intestinal and/or pulmonary microbiological flora. It is not uprising that our authorities keep changing their recommendations after they record different " scientific evidence"