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Table 1 Quality assessment of case–control studies included in this meta-analysis 1

From: Consumption of coffee associated with reduced risk of liver cancer: a meta-analysis

Study Adequate definition of cases Representativeness of cases Selection of control Definition of control Control for important factor or additional factor2 Exposure assessment Same method of ascertainment for cases and controls Nonresponse rate3 Total quality scores
Kuper et al. [11], 2000 - - - 5
Gallus et al. [12], 2002 - - - 6
Gelatti et al. [13], 2005 - - 7
Ohfuji et al. [14], 2006 - - - 6
Tanaka et al. [15], 2007 - - 6
Montella et al. [16], 2007 - - - 6
Wakai et al. [17], 2007 - - 6
Ohish et al. [18], 2008 - - 7
Leung et al. [19], 2011 - - - 5
  1. 1A study can be awarded a maximum of one star for each numbered item except for the item Control for most important factor or second important factor.
  2. 2 A maximum of two stars can be awarded for Control for most important factor or second important factor. Studies that controlled for hepatitis B virus (HBV) or HCV infection received one star, whereas studies that controlled for alcohol drinking received one additional star.
  3. 3 One star was awarded if there was no significant difference in the response rate between control subjects and cases in the chi-square test (P > 0.05).