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PRISMA 2009 flow table
| Records identified through PubMed | 464 |
| Records after duplicates removed | 314 |
| Abstracts screened | 314 |
| Full-text articles assessed for eligibility | 61 |
| Full-text articles excluded | 50 |
| Useful articles | 11 |
| Useful articles from 61 bibliographies | 18 |
| Studies used in the quantitative analysis | 29 |
