Smoking, alcohol consumption, and the risk of extrahepatic cholangiocarcinoma: A meta-analysis

Table 2 Quality of the studies used in this analysis

Author and year	Quality indicators of Newcastle-Ottawa quality assessment scale									Score
	Selection				Comparability		Exposure/outcome
	Ia	Ib	Ic	Id	IIa	IIb	IIIa	IIIb	IIIc
Ghadirian et al[18] 1993	No	Yes	Yes	Yes	Yes	Yes	Yes	No	No	6
Chow et al[19] 1994	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No	No	7
Khan et al[20] 1999	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	7
Zhang et al[21] 2004	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No	No	7
Welzel et al[11] 2007	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No	7
Shaib et al[10] 2007	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	7
El-Serag et al[22] 2009	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes	8
Tao et al[23] 2010	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	7
Cai et al[24] 2011	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	7
Onal et al[25] 2012	Yes	Yes	No	Yes	Yes	No	Yes	Yes	No	7
Brandi et al[26] 2013	Yes	Yes	Yes	Yes	Yes	Yes	No	No	No	6
Zhou et al[27] 2013	Yes	Yes	No	Yes	Yes	No	Yes	Yes	No	7

For case-control studies; Ia: Indicates cases with independent validation; Ib: Indicates consecutive or representative cases; Ic: Indicates community controls; Id: Indicates controls with no history of ECC; IIa: Indicates that study controls were comparable for age and sex; IIb: Indicates that study controls were comparable on all additional factor(s) reported; IIIa: Indicates that the same method of ascertainment was used for cases and controls; IIIb: Indicates that assessment of exposure was from a secure record; IIIc: Indicates that the non-response rate was similar in both groups. For cohort studies; Ia: indicates that the exposed cohort was representative of the population; Ib: Indicates that the non-exposed cohort was drawn from the same population; Ic: Indicates that the exposure ascertainment was from secure records or a structured interview; Id: Indicates that ECC was not present at start of study; IIa: Indicates that the cohorts were comparable for age and sex; IIb: Indicates that the cohorts were comparable on all additional factor(s) reported; IIIa: Indicates that ECC was assessed from a secure record; IIIb: Indicates that follow-up was long enough for ECC to occur; IIIc: Indicates that follow-up was complete. ECC: Extrahepatic cholangiocarcinoma.