“…Recently, MDD has become viewed as a chronic and complex problem rather than acute but transient (Mueller et al, 1999). Several longitudinal prospective studies have contributed much to our evolving understanding of the nature of MDD, including the epidemiological Zurich, Switzerland study (Angst, 1986) and clinical efforts such as the National Institute of Mental Health-Collaborative Depression Study (NIMH-CDS; Katz, Secunda, Hirschfeld, & Koslow, 1979). These studies have revealed that MDD is a chronic problem characterized by complex patterns of remission, recovery, and relapse (Frank et al, 1991).…”