Concordance rates in twin studies measure what?

• A. The rate of genetic mutation
• B. The rate of gene expression
• C. The similarity of a trait between twins
• D. The rate of brain activity

Answer: (C)

Concordance in twin studies is about how similar twins are for a given trait. It’s the likelihood that one twin has the trait when the other twin also has it. This statistic helps researchers gauge genetic influence: if identical twins, who share nearly all their genes, show higher concordance than fraternal twins, that points to a genetic component. It doesn’t measure how often genes mutate, how genes are expressed, or brain activity. So the idea is simply the degree of similarity between twins for that trait.