In psychology and genetics, concordance is the degree of similarity in the presence of a trait, condition, or behavior among individuals, most notably twins. For instance, if both identical twins develop depression, researchers would state that “there is concordance for that disorder”.
In twin and adoption studies, concordance rates are pivotal in gauging the relative influence of heredity and environment on behavior. When identical twins, who share almost all of their genes, present high concordance, it implies a strong genetic influence. Conversely, lower concordance in fraternal twins suggests a stronger environmental impact.
For instance, studies indicate that identical twins have a stronger concordance for schizophrenia than fraternal twins which suggests a genetic influence. Nevertheless, the absence of a 100% concordance supports the fact that upbringing, environment, and experience are just as important. This is especially poignant in the field of behavioral genetics, as it dimensions the interaction between sociocultural and genetic factors that construct psychological conditions.