Table 2. Newcastle-Ottawa quality assessment scale for cohort studies included in this review.
| Studies | Selection |
Comparability | Outcome |
Total score | |||||
|---|---|---|---|---|---|---|---|---|---|
| Representativeness of the exposed cohort | Selection of the non-exposed cohort | Ascertainment of exposure | Outcome of Interest not present at start of study | Assessment of outcome | Adequacy of duration of follow-up | Adequacy of completeness of follow-up | |||
| Marr KA et al., 2004 (19) | A | A | A | A | A | B | A | A | 7 |
| Singh N et al., 2006 (20) | A | A | A | A | A | B | A | A | 7 |
| Upton A et al., 2007 (21) | A | A | A | A | A | B | A | A | 7 |
| Rieger CT et al., 2008 (22) | A | A | A | A | A | B | A | A | 7 |