A technique for studying interaction in small groups. Observers record the source and target of every expressive act and classify the acts into the following twelve categories: shows solidarity, shows tension release, agrees, gives suggestion, gives opinion, gives orientation, asks for orientation, asks for opinion, asks for suggestion, disagrees, shows tension, and shows antagonism. Analysis of protocols has revealed, among other things, two principal types of group leader, namely the task specialist and the social specialist, and leadership in groups is often shared between two people filling these roles. The technique was introduced in 1947 by the US social psychologist Robert Freed Bales (1916–2004) and described in his book Interaction Process Analysis: A Method for the Study of Small Groups (1950). Bales initially studied meetings of Alcoholics Anonymous, the effectiveness of which he was anxious to understand. IPA abbrev.