Studies of Birth Order With Control Group in a Systematic Review, up to 2012.

Abbreviations: CC, case-control study; CI, confidence interval; CS, cross-sectional study; HBeAg, hepatitis B e antigen; HCC, hepatocellular carcinoma; N/R, not reported; OR, odds ratio. aWhen age range was not available, study was categorized as children (<20 years old), adults (≥20 years old) or both children and adults. bAdjusted for age, sex, smoking and anti-HCV. cAdjusted for age, sex, smoking, alcohol, schooling, anti-HCV and sibship size. dStratification by relationship with index case (i.e., children and siblings) was reported.