Table 1

Characteristics of the trials associated with not reporting any or both ethical issues (REC approval and/or request of informed consent from participants). Logistic regression analysis. Odds ratios (OR) and 95 per cent confidence intervals (CI)

Quality indicators (number of trials)Proportion not reporting request of ICPProportion not reporting REC approvalProportion not reporting both request of ICP and REC approvalAdjusted OR* (95% CI)
Trials that acknowledged that they did not obtain the REC (Research Ethics Committee) approval or the ICP (informed consent from participants) are included together with those that did not disclose the information about these issues in the original report.
*A higher odds ratio (OR) means a higher probability of failing to provide information about either or both ethical issues in the original paper. Odds ratios have been also adjusted for journal, country of authors, length of the report, number of participants and source of funding.
†This was the reference category (ref: reference category).
‡p<0.05 (Likelihood ratio test).
§p<0.01 (Likelihood ratio test).
All sample (767)19.829.212.9
Concealment of allocation
Yes (264)†14.824.2 8.01 (ref)‡
No (503)22.531.815.51.66 (1.12–2.46)
Justification of unblinded trials
Yes (36)† 8.319.4 5.61 (ref)‡
No (280) (1.09–6.66)
Type of treatment for control group
Placebo (273)†11.718.7 7.01 (ref)‡
Alternative active treatment (366)21.333.614.51.39 (0.88–2.20)
No treatment (105) (1.37–4.47)
Not a proper control group (23)21.734.817.41.75 (0.52–5.81)
Reporting of statistical methods
Yes: some information reported (739)†18.927.912.01 (ref)§
No information about statistical methods (28)42.964.335.73.77 (1.42–9.98)
Sample size estimation
Shown (320)†14.423.1 6.91 (ref)‡
Not shown (447)23.733.617.21.49 (1.02–2.19)
Rules to stop the trial
Reported (269)†12.121.6 6.41 (ref)‡
Not reported (498)23.732.916.31.33 (0.99–1.78)
Baseline comparison of groups
Presented (679)†18.627.111.61 (ref)‡
Not presented (88)29.545.522.71.80 (1.05–3.08)
Survival (166)†22.930.713.91 (ref)§
Other (601)19.028.812.60.52 (0.33–0.84)