Double dummy is a technique for retaining the blind when administering supplies in a clinical trial, when the two treatments cannot be made identical. Supplies are prepared for Treatment A (active and indistinguishable placebo) and for Treatment B (active and indistinguishable placebo). Subjects then take two sets of treatment; either A (active) and B (placebo), or A (placebo) and B (active).
Double dummy is a method of blinding where both treatment groups may receive placebo. For example, one group may receive Treatment A and the placebo of Treatment B; the other group would receive Treatment B and the placebo of Treatment A.
The figure on the left side is a double-dummy example for a two treatmetn arm scenario. The figure on the right side is a double-dummy example for a three-arm scenario. To maintain the blinding, subjects in each arm will take one tablet and one capsule. In the example on the right side table, subject in placebo arm will take one placebo tablet and one placebo capsule.