doglove

I dropped the ball and just NOW saw your reply regarding BiPolar disorder and diagnosing....

A psychologist/psychiatrist asks questions regarding severity, length, and frequency of symptoms that the patient is having issues with.  There are characteristics to BiPolar I disorder that are very distinct such as the mania (extreme highs, excessive talking, not needing sleep, extreme spending, etc.) and also the severe depression. 

There's also BiPolar II disorder which is a milder form...instead of "mania" there is "hypomania" (not as extreme in nature, but serious enough to be classified). 

I digress....

Psychologists and Psychiatrists use the DSM-IV to help assess and diagnose patients that meet a specific criteria.  The only difference between a psycholgist and a psychiatrist is that psychiatrists have the ability to prescribe medication to patients.  So, more times than not, if a psychologist suspects a severe mental disorder that would require medication to regulate (such as BiPolar I, BiPolar II, Schizophrenia, Major Depressive Disorder, Post Traumatic Stress, etc), the psychologist will refer the patient to a psychiatrist for further evaluation. 

There aren't necessarily a battery of tests that someone goes through to be diagnosed, but there is extension questioning and evaluation regarding the medical/mental history of the patient and his/her family, current symptoms, environmental conditions (changes in marital status, a death in the family, a traumatizing event)..  

Hope this helps you to better understand...sorry for the delay in response!