A type of quantitative research setup where neither the subjects nor the researchers know who has been assigned to the experimental group or the control (placebo) group until after the study is over. Double-blind construction ensures that the researchers do not skew the results by unintentionally affecting subject responses and/or outcomes.

Example: A nurse helping with a study looking at the effects of a new cancer drug is not told whether he is dispensing the actual medication or a placebo.