Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Risk of bias assessment of the nonrandomized studies.
| Studies | Selection | Comparability | Exposure | Total Quality score |
|---|---|---|---|---|
| Jeong (2006) | 2 | 2 | 1 | 5 |
| Lee (2006) | 2 | 2 | 3 | 7 |
| Kim (2007) | 2 | 1 | 1 | 4 |
| Lee (2009) | 2 | 2 | 1 | 5 |
| Lee (2017) | 2 | 2 | 2 | 6 |
| Ahn (2016) | 2 | 2 | 2 | 6 |
| Choi (2016) | 2 | 2 | 1 | 5 |
