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Blind and Double-blind Experiments (page 3)

By — John Wiley & Sons, Inc.
Updated on Sep 16, 2013

Double-Blind Experiments

To be doubly sure that the results of an investigation are not influenced by the prejudice of the investigator, scientists rely on the double-blind experiment. Suppose, for example, a scientist has been much involved in the research on a treatment for the common cold, one that relieves symptoms and actually hastens recovery. Let's say scientist Blackmore has total faith in her new cold remedy and very much wants to see her discovery go over in a big way. The problem is this: How can Blackmore do her experimenting and be totally honest about the results, not kidding herself or anyone else? To do this, she uses a double-blind experimental design.

First, she gets someone she trusts to make up some pills in two batches, one that contains the new treatment for colds and the other one a placebo. Next, she recruits a suitable number of people to take part in the experiment. They are told that they will be randomly assigned to the experimental or to the control group by the tossing of a coin or by taking names out of a hat. The subjects are blind to which group they will be in.

Now, here is where the double-blind factor enters. Blackmore herself does not know which group each subject is in. She gets her trusted associate to give out the pills to each subject, and neither the subjects nor Blackmore knows who receives which one.

After enough time has passed for the subjects to have colds and to use their pills, Blackmore interviews each subject. She questions them about the effectiveness of their treatments and summarizes the effectiveness of each in a report. When she is finished, Blackmore's associate shows her which subjects received the new treatment and which subjects received the placebo pills. Only then can Blackmore and others honestly judge the effectiveness of her cold treatment.

This use of a double-blind experimental design is complex and costly. Even so, it is a very important form of experimenting, and it has great advantages when both subjects and experimenter know too much about the goals of the experiment.

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