Double-blind testing

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By Andy Kaiser 
Article ID: 116

So you want to run a properly controlled, scientifically legitimate test? Better make sure you use double-blind testing.

What is double-blind testing? Why is double-blind testing a good thing?

A double-blind test is a method that can be used in most any testing situation where there is a chance that the results of that test could be affected by the tester or the testee.

In simpler terms, imagine the “Pepsi Challenge”, the taste test where a blindfolded subject sips from one can, then another, and tries to pick which one he likes best. The blindfold makes sure that the taster doesn’t know the brand of the soda before he sips it.

The Pepsi Challenge is a “single-blind” test. A “double-blind” test means that not only the taster is blinded to which soda is which, but the person giving the test is blinded as well. Using our Pepsi Challenge again, making it double-blind would involve making sure the person running the test doesn’t know which brand of soda the taster is tasting!

Double-blind testing helps ensure that the test results are legitimate, and aren’t affected by intentional or unintentional actions of those participating in the test.

Double-blind testing does three things

It prevents the placebo effect. A placebo effect means the subjectivity of the testee could affect the results of the test. So in our soda challenge, imagine the blindfold removed from the taster: If he sees the soda brand before he tastes it, the test results could be different than if he’d “honestly” tasted the soda without knowing the brand.

It prevents experimenter bias. The experimenter could also affect the testing, intentionally or no. This could involve outright cheating or something more subtle, like giving unintended non-verbal queues to the testee.

The controls and placebos are randomized. There must not be any predictable pattern in your testing order. The control group and the placebo group must be mixed together randomly.

Example of double-blind testing

You may have heard of antenna booster stickers, cheap metallic stickers that you can buy for your cellphone. They’re supposed to increase your phone’s reception, decrease static, increase signal strength. See a proper randomized, double-blind test of the cellphone antenna booster sticker.

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