Table 1.

Assessment of study quality

Ref.	Quality indicators from NOS									Score
	Selection				Comparability		Exposure/outcome
	1	2	3	4	5	6	7	8	9
Hong et al[10]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	No	6
Hassan et al[11]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	7
Wang et al[18]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	7
Zhu et al[17]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	7
Ben et al[12]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	7
Berrington de Gonalez et al[9]	Yes	Yes	Yes	Yes	Yes	No	Yes	No	No	6
El-Serag et al[3]	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes	8
Iloeje et al[2]	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	9

NOS: Newcastle-Ottawa quality assessment Scale. For case-control studies: (1) represents cases with independent validation; (2) cases are consecutive or representative; (3) controls are community; (4) controls have no history of pancreatic cancer; (5) study controls are comparable for age and sex; (6) study controls for any additional factor(s); (7) cases and controls have the same method of ascertainment; (8) was follow-up long enough for outcomes to occur; and (9) cases and controls have complete follow-up. For cohort studies: (1) indicates the exposed cohort study representative of the population; (2) the non exposed cohort drawn from the same population; (3) the exposure ascertainment are from secure record or structured interview; (4) the pancreatic cancer was not present at start of study; (5) cohorts are comparable for age and sex; (6) cohorts are comparable for any additional factor(s); (7) assessment of pancreatic cancer is from secure record; (8) follow-up long enough for pancreatic cancer to occur; and (9) complete follow-up.