Be careful when reading research. Don’t be duped by the biological emphasis for depression. Here are two research studies. The first, in a pharmaceutical journal, emphasizes genetic influences. The second, done in the UK, shows sociological influences. As a general rule, the US emphasizes medical model analysis. Other countries have a more psycho-social emphasis.
Depression is influenced by MANY factors. Biology, Learning, Sociological Influences, Adverse Experiences, and so on. Never, ever buy the biology model as the whole truth.