Risk of bias assessment according to the seven biases included in the ROBINS-I tool
| Study authors (year) | Bias 1 | Bias 2 | Bias 3 | Bias 4 | Bias 5 | Bias 6 | Bias 7 |
| Briozzo et al (2006)4 | Unclear | Unclear | Low | Low | High | Unclear | Unclear |
| Labandera et al (2016)14 | Unclear | Unclear | Low | Unclear | High | Unclear | Unclear |
| Kahabuka et al (2017)15 | High | High | Low | Unclear | High | Unclear | Unclear |
| Grossman et al (2018)16 | Unclear | High | Low | Unclear | High | High | Low |