Regier (2013) reports a kappa value of just 0.28 for Major Depressive Disorder while Sartorius reports a figure of 0.3 for mild recurrent depressive disorder, one of lowest figures of all recognized disorders. The diagnosed of ‘mixed anxiety and depressive disorder ‘was just 0.09 with 31% of clinicians saying this was a difficult diagnosis to make.

This is important because it suggests that depression is hard to diagnose reliably, especially if it is mild and presents with anxiety.