
Kurt Lewin (1927). "Gesetz und experiment in der Psychologie" [Law and experiment in psychology]. in: Symposion, Vol 1, p. 375-421. Translated by and cited in: Kurt Kreppner " On the Generation of Data in the Study of Social Interaction1 http://www.scielo.br/pdf/ptp/v17n2/7871.pdf" in: Psicologia: Teoria e Pesquisa Vol 17, nr. 2, p. 109.
1920s