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1Golestan Research Center of Gastroenterology and Hepatology, Golestan University of Medical Sciences, Gorgan, Iran.
2Department of Epidemiology and Oncopathology Research Centre, Iran University of Medical Sciences, Tehran, Iran.
3Department of Public Health, Golestan University of Medical Sciences, Gorgan, Iran.
45th of Azar Hospital, Golestan University of Medical Sciences, Gorgan, Iran.
5Minimally Invasive Surgery Research Center, Rasoul Akram Hospital, Tehran University of Medical Sciences, Tehran, Iran.
6Department of Epidemiology and Biostatistics, Public Health Faculty, Tehran University of Medical Sciences, Tehran, Iran.
© 2013, Korean Society of Epidemiology
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