Table 2. Methodological quality assessment based on the NOS.a .
| Source | Selection | Comparabilityf | Exposure | ||||||
| Definitionb | Representativenessc | Selectiond | Definitione | Ascertainmentg | Methodh | Ratei | Totalj | ||
| Weinstein et al, 2012 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 |
| Gill et al, 2009 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 0 | 8 |
| Key et al, 2007 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 0 | 8 |
| Huang et al, CLUE I 2002 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 0 | 8 |
| Huang et al, CLUE II 2002 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 0 | 8 |
| Goodman et al, 2003 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 |
| Gann et al, 1999 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 0 | 6 |
| Weinstein et al, 2005 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 0 | 6 |
| Cheng et al, 2011 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 0 | 8 |
a
Assessed with the 9-star Newcastle-Ottawa Scale(NOS).
b
Adequate definition of cases(0,1star).
c
Consecutive or obviously representative series of cases (0,1).
d
Selection of controls: Community controls (0,1).
e
Definition of controls: No history of disease (endpoint) (0,1).
f
Study controls for the most important factor or any additional factor(0,1,2).
g
Secure record (eg surgical records) (0,1).
h
Same method of ascertainment for cases and controls(0,1).
i
Same non-response rate for both groups(0,1).
j
Total: minimum equals 1; maximum equals 9 stars.