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Comorbidity: Meanings and Mechanisms


Address reprint requests and correspondence to Michael Rutter, M.D., F.R.S., MRC Child Psychiatry Unit, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF.


Comorbidity, meaning the co-occurrence of two supposedly separate conditions at above chance levels, provides a most important research opportunity. It requires a rigorous examination of diagnostic concepts and a systematic critical testing of those concepts. Such testing may shed much needed light on risk mechanisms. Four issues that have given rise to misunderstanding in this connection are discussed: definitions of terms, diagnostic validity, reassessment and research strategies.