What does it mean if a clinical trial is “randomized”?

A clinical trial is a health-related research study using human beings as the study subjects. Clinical trials are often randomized. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among the treatment groups in the study.

We know -- you’d rather get the new drug, else why participate and get the same old remedy you would have gotten? That’s why studies commonly feature blinded randomization -- that is you are randomly assigned to either the control or the treatment group, and you don’t know (and have no choice of) which one. A double-blinded study means your doctor who is reporting the results of your treatment doesn’t know either (although that information can be "unblinded" if important to your well-being). A “crossover” study means that first you may be randomized to the control group, then after a "washout" period, you’ll move on to the treatment group, or vice versa.

Study design is usually summed up in a string of adjectives in the study title. A typical study might be a “double-blinded, randomized crossover trial of lemon juice versus pepper to control aardvark infestation of earwax.” As you can see, folks with an aardvark issue will be randomly assigned to using lemon juice or pepper, with exposure to both treatments by end of the study, and neither they nor their physician would be aware of to which group they had been assigned. The aardvark might know.