A word about blinded studies.

When possible, medical researchers like to blind, or mask, their clinical trials. In a single-blinded trial, participants do not know whether they are in the intervention group or the control group until the trial ends. In a double-blinded trial, neither investigators nor participants know which group a participant is assigned to until the trial's conclusion.

Blinding is another way of reducing bias that may distort a study's results. For example, investigators may behave differently toward participants whom they know are receiving the experimental intervention.

However, blinding is not always feasible. In a trial comparing surgery with chemotherapy, for example, blinding would be impossible -- both doctors and participants would know which intervention was being applied.

Cancer prevention clinical trials are sometimes blinded, but cancer treatment trials rarely are.

Glossary Terms

In a scientific research study or clinical trial, a flaw in the study design or the method of collecting or interpreting information. Biases can lead to incorrect conclusions about what the study or clinical trial showed.

A clinical trial in which the medical staff, the patient, and the people who analyze the results do not know the specific type of treatment the patient receives until after the clinical trial is over.

A type of clinical trial in which only the doctor knows whether a patient is taking the standard treatment or the new treatment being tested. This helps prevent bias in treatment studies.