Seymour Kety Et Al

Seymour Kety et al. (1978) studied people who had been adopted and who were diagnosed with schizophrenia later in life. What conclusion did the research support?

A) As 12% of biological family members also had been diagnosed with schizophrenia, compared with only 3% of adoptive family members, it was likely there was a hereditary link.
B) As only 3% of biological family members also had been diagnosed with schizophrenia, compared with 12% of adoptive family members, it was likely an environmental link.
C) Both biological and adoptive families had diagnosis rates of 1-2%, so no conclusion was reached.
D) Both biological and adoptive families had diagnosis rates of 15-20%, so no conclusion was reached.