Psychologists could also follow the line of Phrenology
Most people have never heard of Phrenology. This field of studies used to be a type of abstract theory in psychology. Many psychologists leaned into Phrenology because of its link with the medical sciences. Phrenologists aimed to identify character traits and mental states in people according to the configuration of their skull.
Currently, the scientific community considers Phrenology a pseudoscience. In fact, it was banned once better theories were discovered and it eventually went out of practice in 1967. However, these psychologists were incredibly popular up until the early to mid-20th century, and these studies were an improvement from the theories of the time.