Uniform (communicates authority)
In the baseline study, the experimenter wore a grey lab coat.
In one variation, he was called away by an ‘inconvenient’ phone call at the start of the procedure. His role was taken over by an ‘ordinary member of the public’ in everyday clothes.
Obedience fell to 20%, the lowest of the variations.
A uniform is a strong symbol of legitimate authority granted by society. Someone without a uniform has less right to expect obedience.