Family, adoption, and twin studies demonstrate that genetic factors have an important role in certain psychiatric disorders, including schizophrenia, major depressive disorder, and bipolar disorder. The heritability of many psychiatric disorders is high compared with that of other complex disorders such as asthma, diabetes, and stroke. While heritability estimates are high, environmental factors are also critical in determining whether a disorder will develop in a particular individual. For example, the heritability of schizophrenia is estimated to be 82%–85%, yet concordance in monozygotic twins is only 40%–48%.