Detailed information on the risk of bias in included studies
| Authors (year) [ref.] | Bias in the randomisation process | Deviations from intended interventions | Missing outcome data | Bias in measurement of the outcome | Bias in selection of the reported result |
| Bonevski et al. (2021) [14] | Low risk | Low risk | Low risk | High risk: self-reported abstinence data without biochemical validation | Low risk |
| Bullen et al. (2013) [17] | Low risk | Some concerns: adherence to study treatments was significantly higher in the EC group compared to the NRT group due to the trial context: i.e. participants in the EC group were provided with ECs and replacement cartridges, while those in the NRT group were provided with exchange cards redeemable for patches from community pharmacies | Low risk | Low risk | Low risk |
| Hajek et al. (2019) [18] | Low risk | Low risk | Low risk | Low risk | Low risk |
| Lee et al. (2018) [20] | Low risk | Low risk | Low risk | Low risk | Low risk |
EC: e-cigarette; NRT: nicotine replacement therapy.