The early symptoms of major mental disorders, such as bipolar disorder and schizophrenia, can be non-specific, attenuated, or intermittent. These symptoms nevertheless frequently interfere with an individuals' ability to effectively carry-out multiple aspects of their everyday lives, including social, vocational, and educational functioning. Functional changes may in fact occur before individual symptoms reach the threshold for clinical significance. Relying solely on the emergence of early symptoms of psychopathology can delay treatment or lead to the improper selection of treatments that are not effective. Therefore, measuring changes in real-world functioning that correlate with or predate symptoms may be a useful tool for developing an effective treatment plan.