person concepts (including self and groups) and attributes (including valence). Balance–congruity principle When two unlinked or weakly linked nodes are linked to the same third node, the association between these two should strengthen. This is the principle of balance–congruity. The nodes in the principle of balance–congruity are equivalent to the concepts in Heider's balance theory, and the three involved nodes/concepts make up a system. Since every relationship within the system here is positively associated, this, according to a derivation of Heider's theory, also represents a balanced system where the product of the direction of all associations within the system is positive. Balanced-identity research design In 2002, Greenwald and his colleagues introduced the balanced-identity design as a method to test correlational predictions of Heider's balance theory. The balanced identity design incorporated Heider's theory, the balance–congruity principle, and the assumption of centrality of self. The assumption of centrality of self is that in an associative knowledge structure, the self's centrality can be represented by its being associated with many other concepts that are themselves highly connected in the structure. The concepts in a typical balanced identity design are the self, a social group/object, and either a valence attribute or nonvalence attribute. There are thus five important associations possible in a typical balanced identity design that connect these three categories of concepts. An attitude is the association of a social group/object with a valence attribute; a stereotype is the association of a social group with one or more nonvalence attributes; self-esteem is the association of the self with a valence attribute; a self-concept is the association of the self with one or more nonvalence attributes; and the last important association is between the self and a social group/object, which is called an identity. However, in a typical balanced identity design, only three of the five possible associations come into play, and they are usually either identity, self-concept, and stereotype or identity, self-esteem, and attitude. Researchers using a balanced identity design are the ones to determine the set of concepts they want to investigate, and each one of the associations within the system that the researchers created will then be tested and analyzed statistically with both implicit and explicit measures. Typical results of balanced-identity research design with implicit measures A typical result of a balanced identity design usually shows that a group's identity is balanced, at least with implicit measures. According to a derivation