Table 3.
Trial attributes influencing internal validity
| Attribute | N(%) Reporting |
|---|---|
| Purpose of trial | |
| Demonstrate superioritya | 235/290 (81.0) |
| Demonstrate equivalence or non-inferiority | 43/290 (14.8) |
| Assess safety | 11/290 (3.8) |
| Feasibility | 1/290 (0.3) |
| Formal sample size and power calculation | |
| Not reported | 106/290 (36.6) |
| Reported | 184/290 (63.4) |
| Calculation included all elements | 160/184 (87.0) |
| Calculation allowed for dropouts and attrition | 78/184 (42.4) |
| Primary endpoint | |
| Not reported | 45/290 (15.5) |
| Reported | 245/290 (84.5) |
| Composite primary endpoint | 35/245 (14.3) |
| Single objective primary endpointb | 159/245 (64.9) |
| Subjective primary endpoint | 51/245 (20.8) |
| Reported provenance of scale | 24/51 (47.1) |
| Reported validity | 1/51 (2.0) |
| Reported reliability | 2/51 (3.9) |
| Reported sensitivity | 0/51 (0.0) |
| Reported blinding of primary outcome assessor | 20/51 (39.2) |
| Type of control group | |
| Concurrent | 282/290 (97.2) |
| Historical | 8/290 (2.8) |
| Nature of comparator | |
| Placebo or sham procedure | 11/290 (3.8) |
| Alternative operative intervention | 220/290 (75.9) |
| Non-operative intervention | 59/290 (20.3) |
| Allocation method | |
| Deterministicc | 30/290 (10.3) |
| Randomization | 256/290 (88.3) |
| Minimizationd | 4/290 (1.4) |
| Allocation concealment (256 randomized trials only) | |
| Method described for generation of random allocation sequence | 105/256 (41.0) |
| Identification of person or entity generating the sequence | 82/256 (32.0) |
| Provided assurance that sequence was concealed until allocation | 132/256 (51.6) |
| Blinding | |
| Trial reported some element of blinding | 114/290 (39.3) |
| Participants reported blinded | 41/114 (36.0) |
| Interventionist reported blinded | 14/114 (12.4) |
| Primary outcome assessors reported blinded | 46/114 (40.4) |
| Maintenance of blind reported assessed | 5/114 (4.4) |
| Trial execution | |
| Participants receiving treatment as allocated | |
| Treatment received by allocation not reported | 27/290 (9.3) |
| <85% of intervention participants received intervention | 13/263 (4.9) |
| <85% of control participants received control condition | 8/263 (3.0) |
| Full crossover data not reported (256 randomized trials only) | 29/256 (11.3) |
| >10% crossovers, intervention to control | 17/227 (7.5) |
| >10% crossovers, control to intervention | 9/227 (4.0) |
| Follow-up | |
| Full data regarding completeness of follow-up not reported | 41/290 (14.1) |
| Reported follow-up in entire sample only | 30/249 (12.0) |
| <90% intervention participants completing follow-up | 59/219 (26.9) |
| <90% control participants completing follow-up | 58/219 (26.5) |
One trial was powered to show non-inferiority but the authors interpreted findings of “no significant difference” as supporting the claim that the surgical procedure under investigation was superior on the grounds that surgery, in contrast to medical therapy, corrected the anatomic defect thought to be responsible for the pathophysiology of the disease. We classified this trial as a superiority trial due to the ultimate claims made by the authors.
Objective endpoints were defined as those which were externally verifiable, i.e. re-admission or morbidity.
One trial was described as being randomized, but used hospital registration numbers for allocation (even to one group and odd to the other). This trial was recorded as deterministic.
One trial began with a strategy of minimization, but switched to randomization midway. This trial was recorded as using minimization.