In the late 19th century a series of remarkable discoveries in physics were made including X-rays and radioactivity. A new world of physical phenomena was being uncovered by scientists, and hopes of new discoveries were high. It was thus in 1903 that the French physicist Prosper-René Blondlot announced that he had discovered a new form of radiation which he christened N-rays after the University of Nancy where he worked. The problem was that N-rays were difficult to detect and several scientists had problems reproducing Blondlot’s experiments. So the British Journal Nature sent the physicist Robert Wood to Blondlot’s lab to witness an N-ray demonstration.
The demonstration involved an N-ray producing machine that relied on a prism made of aluminum to generate the rays. The room was darkened, the machine was started, and the N-ray measurements were begun. But Wood, who had a reputation as a debunker, removed the prism from the machine - something that would have caused the N-rays to cease to be produced. However, Blondlot and his assistant kept making the N-ray readings as if nothing had happened. This and other evidence led Wood to conclude that this radiation did not exist, and that what Blonlot was detecting was only present in his imagination.
The N-ray story is a classic example of experimenter bias. When a scientist is performing measurements that involve a subjective component, there is the danger that the scientist will see what he or she wants to see. The common solution to this problem is to make the scientist blind. Thankfully this does not involve gouging their eyes out, but rather coding the samples to be evaluated. In this way the experimenter is “blind” to the identity of the samples and thus the bias is eliminated. These blind protocols are routinely applied in science whenever there is a chance that knowing the identity of the samples will affect their reading.
But the complexity of the human mind to warp the scientific enterprise goes beyond the laboratory. In clinical trials a very well-known phenomena is the placebo effect. In this effect the patient experiences an improvement in their condition after being administered an inert substance or exposed to a procedure that should not be effective at treating their ailment. To avoid experimenter bias and the placebo effect, clinicians implement what is called a double blind protocol where both the doctor and the patient do not know the identity of the treatment.
Not controlling experimenter bias can lead to bad science. So, you see, the only good scientist is a blind scientist!
The image from Archive.org is in the public domain.