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NOTICE: this is the author’s version of a work that was accepted for publication in the Journal of Health Psychology. Changes resulting from the publishing process, such as copy-editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. A definitive version of this work was published by Sage Publications in the Journal of Health Psychology, 14(1): 36-42, 2009, this version can be found at http://dx.doi.org/10.1177/1359105308097941 (Please note: access via this link may only be available with a subscription).