I hope you are approved when you apply. It probably is true@hard to get for non-physical disorders. I am on SSI for panic disorder/agoraphobia, depression. Got approved the 2nd try with a disability advocate appearing before the judge on my behalf. I have 2 friends on SSI also for mental disorders, one for bipolar. If my memory is correct there are some people on for MDD. Yes there's a scale of partial inability of some kind. If you are able to work to a certain degree, your SSI amount will be less.