As this study was nested in a clinical study, in the first step we adjusted for allocation in the clinical study, and in the second step we adjusted for allocation in the clinical study as well as for age and gender.
A study by Wu et al. (2002) [ 4] compared valacyclovir and acyclovir as prophylactic regimens for cytomegalovirus, stratifying EQ-5D results by presence or absence of adverse events, without regard to treatment allocation in the study.
Fourth, we identified limited allocation concealment in the CB studies as well as healthcare facility-based studies.
Physicians, as well as medical assessors, were blinded to the allocation of patients in the study groups.
As the group under study is heterogeneous with regard to some key variables, minimisation was chosen as a method for allocation in order to minimise the imbalance between the treatment groups with respect to baseline characteristics [ 30].
Figure 2 shows details of the treatment allocation and the reasons for not progressing in the study.
As all practices were included in the study at one time there was no need to balance the allocation sequence.
On the basis of the procedures employed in the study, allocation concealment was classified as adequate, inadequate or unclear [ 32].
21 28–30 31 There was not sufficient information about random allocation used in most studies as only 3 of these (33%) described random allocation 21 29 31 and only 33333%) provided sufficient information about allocation concealment at the time of outcome assessment.
Treatment (betacarotene supplements and/or daily sunscreen) allocation in the trial 1992-1996 was included as a study design variable.
Of the 17 randomised controlled studies sequence generation was considered adequate in thirteen studies, as was allocation concealment.
