Personality assessment is perhaps more an art form than a science. In an attempt to render it as objective and standardized as possible, generations of clinicians came up with psychological tests and structured interviews. These are administered under similar conditions and use identical stimuli to elicit information from respondents. Thus, any disparity in the responses of the subjects can and is attributed to the idiosyncrasies of their personalities.
Moreover, most tests restrict the repertory of permitted of answers. “True” or “false” are the only allowed reactions to the questions in the Minnesota Multiphasic Personality Inventory II (MMPI-II), for instance. Scoring or keying the results is also an automatic process wherein all “true” responses get one or more points on one or more scales and all “false” responses get none.
This limits the involvement of the diagnostician to the interpretation of the test results (the scale scores). Admittedly, interpretation is arguably more important than data gathering. Thus, inevitably biased human input cannot and is not avoided in the process of personality assessment...