Risk of bias for included studies
| Author (year) | Goal: to judge the risk of selection bias | Goal: to judge the risk of attrition bias | Goal: to judge the risk of measurement bias related to how PF was measured | Goal: to judge the risk of bias related to the measurement of outcome | Goal: to judge the risk of bias due to confounding | Goal: to judge the risk of bias related to the statistical analysis and presentation of results |
| Levine et al 7 | Low | N/A | Low | Low | Low | Low |
| Boyd et al 6 | Low | N/A | Low | Low | Low | Low |
| Rudolph et al 10 | Low | N/A | Low | Low | Moderate | Low |
| Vilke et al 12 | Low | N/A | Low | Low | Low | Low |
| Vilke et al 13 | Low | N/A | Low | Low | Moderate | Low |
| Wampler et al 14 | Low | N/A | Low | Low | Moderate | Low |
| Heyerdahl et al 26 | Low | Low | Low | Moderate | High | Low |
N/A, Not applicable.