Table 3.

Newcastle Ottawa quality assessment scale for 7 studies.

		Ban Seok Lee	Mariko Tsukagoshi	Benjamin Goeppert	Yu Jin Lim	Benjamin Goeppert	Gu Fang-Ming	TARO OSHIKIRI
Selection
Was the case definition adequate?	Yes, with independent validation	☆	☆	☆	☆	☆	☆	☆
	Yes, eg record linkage or based on self reports
	No description
Representativeness of the cases	Consecutive or obviously representative series of cases	☆	☆	☆	☆	☆	☆	☆
	Potential for selection biases or not stated
Selection of Controls	Community controls		☆					☆
	Hospital controls
	No description
Definition of controls	No history of disease(endpoint)	☆	☆	☆	☆	☆	☆	☆
	No description of source
Comparability
Comparability of cases and controls on the basis of the design or analysis	Study controls for (selecting the most important factor)	☆	☆	☆	☆	☆	☆	☆
	Study controls for any additional factor
Exposure
Ascertainment of exposure	Secure record (eg surgical records)	☆	☆	☆	☆	☆	☆	☆
	Structured interview where blind to case/control status
	Interview not blinded to case/control status
	Written self report or medical record only
	No description
Same method of ascertainment for cases and controls	Yes	☆	☆	☆	☆	☆	☆	☆
	No
Non-Response rate	Same rate for both groups
	Non respondents described Rate different and no designation
Score		6	7	6	6	6	6	7