5X5 Episode 77
|5X5 Episode 77|
|9th September 2009|
|5X5 76||5X5 78|
|S: Steven Novella|
|R: Rebecca Watson|
|B: Bob Novella|
|J: Jay Novella|
|E: Evan Bernstein|
The Double-Blind Protocol in Science
You're listening to the Skeptics' Guide 5x5, five minutes with five skeptics, with Steve, Jay, Rebecca, Bob and Evan.
S: This is the SGU 5x5 and tonight we are talking about double blind testing. The double blind refers to a protocol in scientific studies in which both the examiner (the researcher) and the subject do not know critical details about the study itself. Specifically, if we use for example a medical test, the subject receiving the treatment doesn't know if they are getting a real treatment or a placebo (a fake treatment). And the person examining them to figure out how they are responding to the treatment also doesn't know if they received the real treatment or the placebo. The purpose for blinding is to control for variables in the study, just like science is always about controlling for variables, by doing this you eliminate all of the psychological and bias and expectation variables and you isolate the treatment itself or whatever, whatever is the subject of the scientific experiment.
E: And one of the earliest suggestions that a blinded approach to doing experiments would be handy, or valuable, came from Claude Bernard who was once named "one of the greatest men of all science". He was a physiologist from the mid-nineteenth century and he recommended that any scientific experiment should be split between the theorist who conceived the experiment and a naive observer who registers the results without foreknowledge of the theory or hypothesis that's being tested, and this suggestion was in stark contrast to the enlightenment era attitude that scientific observation can and should only be valid when it was undertaken by someone who was well educated and an informed scientist. So this was pretty much opposite of that mind set and it turned out to be revolutionary.
B: A good example of double blinding involves forensics, specifically criminal identification. Often a police officer will show a witness pictures of people in hopes the main suspect will be picked. We have all seen that scenario played out over and over in many different TV shows and movies. This is a single blind test. The problem is that the officer could unknowingly steer the witness to the preferred suspect by the way he talks, by the way he— even the hand gestures and all these subtle cues that the officer might not realize that he is giving to the witness. Therefore it is becoming more common nowadays to do double blind identification by bringing in an officer that is unfamiliar with the case to show the pictures to a witness which would then prevent any of these subtle cues from coming through because this police officer doesn't know who the primary suspect is so he can't unconsciously cue who it is.
R: A good example of something that we could have investigated better if people looked at the placebo effect is the Clever Hans phenomenon in which people thought that a horse could do math just by tapping out his hoof — which we've covered in the past on SGU. And what it turned out to be was that the man who owned the horse was giving the horse subtle clues as to what point to stop tapping his hoof. For instance someone from the audience would say "what is 3+2?", the horse would tap out 5 beats and even the person who owned the horse thought that he was for real. He didn't realize that he was giving the horse the subtle clue as to what point to stop tapping. If that experiment had been double blinded then they could have ruled out the experimenter's own bias that was unconsciously influencing the experiment and they would have seen that it was actually that that was causing Clever Hans to stop tapping his little hoof.
J: You know double blind experiments don't only apply to scientists, you know in a laboratory, you could do this at your school, like say you are performing some type of experiment in science class like the absorption of paper towels — of different paper towels. You could use the double blind protocol in your experiment and see how the results are different when you use it versus when you don't use it.
S: That's right, and it does apply also out of not just in medicine, which I think is the context that people most readily think of. For example N-rays, N-rays were all the rage back in 1903 after X-rays were discovered, other researchers thought they had discovered another kind of ray called N-rays but they could only be seen under certain conditions by certain people. They were not observing it in a blinded way, when the N-rays were supposed to be there they saw them and when they were not supposed to be there they didn't see them, and then when they were investigated in a double blind way they didn't know whether or not the prism that made the N-ray that allegedly made the N-rays appear were in the equipment or not, their results did not match the predicted results. So blinding made N-rays vanish. Blinding the experimenter is critical beyond just the context of medicine, whenever you want to eliminate bias or expectation from the results. And as Evan said, the double blinding technology or protocol has revolutionized science.
S: SGU 5x5 is a companion podcast to the Skeptics' Guide to the Universe, a weekly science podcast brought to you by the New England Skeptical Society in association with skepchick.org. For more information on this and other episodes, visit our website at www.theskepticsguide.org. Music is provided by Jake Wilson.