Fig. 3

Effect of age, period, and birth cohort on the relative risk of primary liver cancer incidence with APC regression analysis in Sihui county by sex. a Age effects; b, Period effects; c, Birth cohort effects. The age effects for both sexes showed that the risk of PLC increased with age. Compared with the age group of 55–59 years, the RR of PLC was up to 3.61(95 % CI:2.20–5.96) for males and 3,86 (95 % CI:1.78–8.36) for females in the oldest age group (80–84 years) (Fig. 3a). Period effects for males depicted that the RRs decreased from 1987–1991 to 1997–2001, and then plateaued afterwards; for females, RR fluctuated through the entire period. The RRs increased from period1987-1991 to 1992–1996, decreased consistently from 1992–1996 to 2002–2006, and then increased to the staring risk (Fig. 3b). By using the 1940–1944 birth cohort as the reference group, an obvious increased incidence trend in both males and females were obtained; however, females had a plateau in the youngest cohorts who were born during 1955–1974 and males had a sharp increasing trend in the cohorts who were born during 1965–1974 (Fig. 3c)