A mathematical model of opinion change was tested interrelating 3 fundamental factors affecting social influence: the weight accorded the influencer's opinion by the subject (the communicator's credibility); the weight the subject accorded his own initial viewpoint (the subject's self-confidence); and the size of the difference in opinion between the subject and the communicator (the opinion discrepancy). A total of 60 responses was obtained from the 39 subjects who were students in an introductory course in psychology. The experiment was successful and established which of the formulae tested predicted opinion change more precisely. A second study, stimulated by the first, is on "The Relationship of Inertia to Toward and Away Forces in Opinion Change: An Extension of the'Balanced Force' Model." Findings suggested that "three social influence factors added their effects, and the inertia force--commitment--had more than just a resistance effect: it had an away effect. This finding is consistent with the boomeranging found in the previous study." (Author/JS)