Refer to the passage below and then answer the question afterwards in the same language as the passage:

Passage: Twin studies are utilized in an attempt to determine how much of a particular trait is attributable to either genetics or environmental influence. These studies compare monozygotic and dizygotic twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from epigenetic and environmental influence. Twins that have been separated early in life and raised in separate households are especially sought-after for these studies, which have been used widely in the exploration of human nature.  Classical twin studies are now being supplemented with molecular genetic studies which identify individual genes.

Question: What kind of method is utilized?
Twin studies