Anything Causes Everything (Depressing)

Today’s classroom exercise: Decide whether the technique used in this study can be used to prove that any particular thing can cause any other particular thing:

Inflammation, Sanitation, and Consternation — Loss of Contact With Coevolved, Tolerogenic Microorganisms and the Pathophysiology and Treatment of Major Depression,”
AUTHORS: Charles L. Raison, MD; Christopher A. Lowry, PhD; Graham A. W. Rook, BA, MB, BChir, MD, FSB
PUBLISHED IN: Archives of General Psychiatry, Vol. 67 No. 12, December 2010. The authors, at Emory University, University of Colorado, Boulder, and University College London, suggest that excessive cleanliness in the modern world — and the consequent lack of exposure to provocative germs — is a likely cause of widespread ” major depressive disorder”.