2. Psychiatric illnesses are based on whether or not a patient meets certain criteria. Major depression, for instance: https://www.ncbi.nlm.nih.gov/books/NBK64

2. Psychiatric illnesses are based on whether or not a patient meets certain criteria. Major depression, for instance: https://www.ncbi.nlm.nih.gov/books/NBK64063/ https://www.ncbi.nlm.nih.gov/books/NBK64063/ These criteria are, to some degree, subjective and also easily gamed since in many cases doctors are relying upon noisy / potentially flawed input from patients (i.e., it's possible to game the system to get adderall, etc). However, the DSM, in providing these criteria and the number that need to be expressed to constitute a disorder, are establishing some measure of objectivity. While it is certainly imperfect, it's far from the state of affairs in the 40s/50s and definitely not purely subjective. More objective / less noisy and biased criteria would certainly be welcome, but they don't really exist and that's been a major goal of NIMH as late. Some people have attempted to predict the presence of mental illness using fMRI scans, with limited success: http://fcon_1000.projects.nitrc.org/indi/adhd200/results.html http://fcon_1000.projects.nitrc.org/indi/adhd200/results.htm... However, even without reliable diagnosis via fMRI, I've noticed some psychiatrists using tasks from psychophysics to aid in diagnosis. Unfortunately they aren't always as savvy as scientists with respect to test-retest reliability, but it's a start.