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

<p>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.</p>a<p>When age range was not available, study was categorized as children (<20 years old), adults (≥20 years old) or both children and adults.</p>b<p>Adjusted for age, sex, smoking and anti-HCV.</p>c<p>Adjusted for age, sex, smoking, alcohol, schooling, anti-HCV and sibship size.</p>d<p>Stratification by relationship with index case (i.e., children and siblings) was reported.