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Table 2 Characteristics of studies and evaluation of Newcastle-Ottawa Scale

From: Causal assessment of smoking and tooth loss: A systematic review of observational studies

        NOS
Study design First author, year Participants Age range (years) Definition of tooth loss Focal point Dose-response Coding Score
Cross-sectional study Randolph, 2001 3,050 Mexican American 65-99 15+ F NA 011 11 1 5*
  Klein, 2004 2,764 American 53-96 1+ F NA 011 11 1 5*
  Tanaka, 2005 1,002 Japanese pregnant women 29.8 on average 1+ S NA 010 11 0 3
  Hanioka, 2007 2,200 Japanese 60-94 Total tooth loss S NA 101 10 1 4
  Musacchio, 2007 1,226 Italian males 65+ Total tooth loss S NA 101 11 1 5*
  Ojima, 2007 1,314 Japanese 20-39 1+ S 3/4 levels 111 01 1 5*
  Hanioka, 2007 3,999 Japanese 40-94 9+ S 3/4 levels 111 11 1 6*
  Mundt, 2007 2,501 German 25-59 15th percentile F 3 levels 111 11 1 6*
  Yanagisawa, 2009 547 Japanese males 55-75 9+ S 3 levels 110 11 0 4
  Yanagisawa, 2010 1,088 Japanese males 40-75 9+ S 3 levels 110 11 0 4
        NOS
Study design First author, year Participants Age range (years) Duration of observation Focal point Dose-response Coding Score
Cohort study Slade, 1997 693 Australian 60+ 2 years F NA 10 01 110 4
  Krall, 2006 789 American males 21-84 36 years S NA 00 11 111 5*
  Okamoto, 2006 740 Japanese males 30-59 4 years S 3 levels 00 10 110 3
  Dietrich, 2007 43,112 American male health professionals 40-75 16 years S 5 levels 01 11 111 6*
  Cunha-Cruz, 2008 12,264 American HMO members 45-61 3 years A NA 00 10 110 3
  1. Studies were conducted in Japan, the United States, Australia, Germany and Italy. A dose-response relationship was examined in 7 studies, and 8 studies (6 for cross-sectional and 2 for prospective cohort studies) were classified as high quality.
  2. S, smoking; F, factors including smoking; A, systemic antibodies; *evaluated for high-quality methodology by the modified Newcastle-Ottawa Scale (NOS). One star each was given for six and seven items for cross-sectional and cohort studies, respectively, if the methodology of a study satisfied the criterion. The items were divided according to three categories of selection, comparability and exposure for cross-sectional studies and selection, comparability and outcome for cohort studies. When a study satisfied all criteria, the star column appears as 111 11 1 for cross-sectional and 11 11 111 for cohort studies. Studies with total scores of five or more, three or four, and two or less were evaluated as high-, moderate- and low-quality studies, respectively.