Myles 2011.
| Methods | Secondary data analysis of a multi‐centre RCT (subgroup) | |
| Participants | 446 adult patients scheduled for major abdominal surgery for primary cancer without metastasis | |
| Interventions | Intraoperative and postoperative epidural analgesia vs general anaesthesia alone (IV opioids) | |
| Outcomes | Primary endpoint: progression‐free survival; secondary endpoint: overall survival, time to tumour progression | |
| Notes | 915 participants were included in the prospective multi‐centre trial; 506 of those had undergone surgery for cancer, and 3 were unclassified/excluded. 31 participants were excluded because of metastasis at the time of surgery. 26 additional participants were excluded because they were lost to follow‐up or refused to provide consent | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | Randomization for the original study was based on use of random permuted blocks within each institution, and was maintained and allocated to each institution by a central trial secretariat at the Department of Public Health. Baseline characteristics of the analysed subgroup are reported and comparable |
| Allocation concealment (selection bias) | Low risk | Random permuted blocks used, assigned by central allocation |
| Blinding of participants and personnel (performance bias) All outcomes | Low risk | Participants and caregivers were not blinded. Likely no influence on outcome |
| Blinding of outcome assessment (detection bias) All outcomes | Low risk | Blinding of outcome assessment was not reported. However, it was judged unlikely that outcome assessment was influenced by lack of blinding |
| Incomplete outcome data (attrition bias) All outcomes | Low risk | In all, 26 cases (14 participants in the study group and 12 in the control group) were lost to follow‐up and were not included in the data analysis. Characteristics of this group have not been reported Only 4 (< 1%) of the participants had incomplete (censored) data within the first 5 years after surgery Missing outcome data are unlikely to be related to survival outcomes |
| Selective reporting (reporting bias) | Low risk | No study protocol was available. One secondary outcome (TTR) was not specified or defined in the methods section of the published article but was reported in the results section. Primary outcome was reported in accordance with the methods section of the published study |
| Other bias | Low risk | The number of included participants varies between 445 (forest plot), 446 (text) and 447 (flow chart), most likely as the result of calculation error. However, as the difference is only 1 among more than 450 participants, we find that this most likely does not introduce bias |