In my experience, anxiety can often coexist with depression. For some people, anxiety is the the main problem and overtime, due to the problems that the anxiety creates, this will then lead to depression as a "secondary" phenomenon. On the other hand, some people have a predominant depressive disorder. They often feel flat, sad and "sluggish" and due to the dysfunction and problems that these symptoms create, these can then lead to stress and anxiety.
Knowing which one is more predominant can help us as Doctors, to manage the problem with certain types of medications if this is appropriate and also helps us to focus on certain areas in the counselling approach to the problem.
These points will be further elaborated in future publications.