Biological and Medical Sciences
The complexity of living systems and the ethical impossibility of performing fully controlled experiments with certain species of animals and humans provide a rich, and difficult to control, source of experimental bias. The scientific knowledge about the phenomenon under study, and the systematic elimination of probable causes of bias, by detecting confounding factors, is the only way to isolate true cause-effect relationships. It is also in epidemiology that experimenter bias has been better studied than in other sciences.
A number of studies into Spiritual Healing illustrate how the design of the study can introduce experimenter bias into the results. A comparison of two studies illustrates that subtle differences in the design of the tests can adversely affect the results of one. The difference was due to the intended result: a positive or negative outcome rather than positive or neutral.
A 1995 paper by Hodges & Scofield of spiritual healing used the growth rate of cress seeds as their independent variable in order to eliminate a placebo response or participant bias. The study reported positive results as the test results for each sample were consistent with the healers intention that healing should or should not occur. However the healer involved in the experiment was a personal acquaintance of the study authors raising the distinct possibility of experimenter bias. A randomized clinical trial, published in 2001, investigated the efficacy of spiritual healing (both at a distance and face-to-face) on the treatment of chronic pain in 120 patients. Healers were observed by "simulated healers" who then mimicked the healers movements on a control group while silently counting backwards in fives - a neutral rather than should not heal intention. The study found a decrease in pain in all patient groups but "no statistically significant differences between healing and control groups ... it was concluded that a specific effect of face-to-face or distant healing on chronic pain could not be demonstrated."
Read more about this topic: Experimenter's Bias
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