I thought those were the psychologists who only had 6 months minimal training to prescribe certain drugs.
My granny worked in and around the field for most of her professional career. Generally they can accurately determine the problem thanks to various tests, or with close consultation with the psychologists. But response to medication can also be a great determining factor. In many cases if they prescribe low doses of the medication to begin with and usually there will be a noticeable improvement if they've diagnosed correctly. There's also a range of different medications for each condition and while some can be easily identified as the ideal one, in many cases it really is just a case of trial and error to see which suits best.
The bad prescription cases she usually came across were with patients who had been prescribed medication early in the diagnosis, or had been through many different doctors who prescribed or altered existing prescriptions to achieve better results without having a full understanding of the whole issue. The general reaction to this was to simply strip back every medication they could so they could re-evaluate correctly. But the vast majority of problems they had weren't with bad perscriptions but children simply growing up and the body changing constantly, requiring different dosages or even different prescriptions altogether.
*meh* My Granny also had the advantage of working in a team unlike many psychiatrists who have to rely on only their own perceptions and knowledge.
