Schachter’s affiliation experiments the earliest attempts to study affiliation in a systematic fashion. In one study, a group of female participants were told that they would be taking part in an experiment in which painful but harmless electric shocks would be administered. Another group were told that they would be given painless electrical shocks. Both groups would have to wait for ten minutes prior to the procedure, and could choose to wait either with others or alone. The result showed that a significantly higher number of women who were to recieve the painful shocks, chose to wait with other women. Schachter presented the results of this study and others in 1959, in his influentual book The Psychology of Affiliation: Experimental Studies of the Sources of Gregariousness.
Gilbert, D.T., Fiske, S. T. & Lindzey, G. (Eds.) (2010). The handbook of social psychology (4th ed., Vol. 2, pp. 866–867)