CialdiniR. B.SchroederD. A.Increasing compliance by legitimizing paltry contributions: When even a penny helps. Journal of Personality and Social Psychology, 1976, 34, 599–604.
2.
CialdiniR. B.VincentJ. E.LewisS. K.CatalanJ.WheelerD.DarbyB. L.Reciprocal concessions procedure for inducing compliance: The door-in-the-face technique. Journal of Personality and Social Psychology, 1975, 31, 206–215.