He is survived by his second wife, Trudy Bradley, whom he married in 1969. Festinger became a major figurehead in the post-World War II push to turn social psychology into a rigorous experimental discipline. One of his works of the time was Research Methods in Behavioral Sciences, which he wrote with Daniel Katz in 1953. Under influence from Lewin' style, Festinger created several theories involving informal social influence, communication in small groups, and social comparison processes. Thus came about his most widely known work, A Theory of cognitive Dissonance in 1957.
Dissonance produces tension or stress.
The amount of dissonance depends on number of factors. The amount of dissonance equals the number of dissonant cognitions times their importance, divided by the number of cognitions times their importance. When dissonance is produced, people are motivated to reduce it. Samelson directly states that cognitive dissonance and its spin-offs dominated the literature of social psychology in the United States for a decade or more, while at the same time spreading to other disciplines, such as political science, and catching on in other countries including German experimental social psychology. It even became a catch phrase on the evening news as it entered the American lexicon.