Three studies also reported adequate generation of allocation sequence, allocation concealment and blinding of service providers and outcomes assessors.
Of the 33 trials, 18 reported adequate generation of allocation sequence and adequate allocation concealment and 24 reported adequate masking of participants, staff, and outcome assessors.
It was conducted with an adequate generation of allocation sequence; adequate allocation concealment; adequate reporting of all relevant outcomes; had very few dropouts; and was conducted on a not-for-profit basis.
The tool (which can be applied to both randomized and non-randomized studies) verifies study attributes that are possible sources of bias, including adequate generation of the allocation sequence, concealment of the allocation to the different conditions, preclusion of knowledge of the allocated interventions (blinding of assessors) and handling of incomplete outcome data.
Berger [ 13] has added to the debate by presenting the logical consideration that successful control for bias cannot be assured on a basis of inclusion of adequate methods, (adequate generation of random sequence, allocation concealment, blinding/masking) alone.
Such assessment of internal trial validity is based on the understanding that successful control for systematic error cannot be assured on the basis of inclusion of adequate methods alone; i.e. adequate generation of random sequence, allocation concealment, blinding/masking, as part of the trial methodology.
African trials were three times more likely than North American trials to report adequate allocation concealment (OR = 3.24; 95%CI: 1.59 to 6.59; p<0.01) and twice as likely to report adequate generation of the sequence (OR = 2.36; 95%CI: 1.20 to 4.67; p = 0.01), after adjusting for other confounding factors.
We judged RCTs to be of adequate quality if their generation of allocation sequences was unpredictable, if methods of allocation concealment ensured patients and investigators could not foresee treatment assignment, and if patient attrition was clearly described.
Risk of bias [46]: Sequence, adequate sequence generation; Allocation, allocation concealment; Blinding, blinding outcome assessor; Outcome, incomplete outcome data; Report, selective outcome reporting; Other, other sources of bias.
The generation of allocation sequence was adequate in 31 (38.8%) reports; treatment allocation was concealed in 21 (26.3%).
We have since been informed by the author of the published manuscript that although generation of allocation sequence was adequate for the first participant, alternation was used for subsequent participants.
