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Halvorsen PA, Wennevold K, Fleten N, Muras M, Kowalczyk A, Godycki-Cwirko M, Melbye H.Halvorsen PA, et al.Scand J Prim Health Care. 2011 Jun;29(2):110-6. doi: 10.3109/02813432.2011.555382. Epub 2011 Feb 17.Scand J Prim Health Care. 2011.PMID: 21323635Free PMC article.