We originally planned to use a postponed informed consent procedure, 19 whereby patients would be asked to consent to having full information withheld about the study (particularly the exact nature of the intervention) until after follow-up.
Of the 439 individuals who were eligible for screening (the source of data for the present study), 29 declined to continue in the study, 11 could not be contacted, and 5 postponed the consent process, resulting in 394 people (90%) who provided informed consent.
To prevent selection bias, a postponed informed consent procedure was used to blind all participants in both study arms [ 20].
With regard to the intervention, a postponed informed consent procedure has been chosen to blind all participants in both arms [ 15].
First, the internal validity is good firm because it is a cluster RCT with postponed informed consent, limiting the risk of response bias in both groups.
The study will be double-blinded as patients will be blinded to the intervention by using a postponed informed consent procedure described by Boter et al [ 17].
This postponed informed consent procedure has shown to be a valuable solution to obtain valid assessment of subjective outcomes in a trial in which patients cannot be blinded to the intervention[ 15, 16], also in patients with COPD [ 17].
According to the maxim of postponed informed consent, only the adult would be truly able to determine the best interests of the child he or she was in a former time.
Due to the postponed informed consent procedure there was a loss of participants in the ISAR-PC positive group of the intervention arm, as they found the full extent of the study too time consuming or overwhelming.
Some subjects did not provide a buccal swab sample at inclusion, because they were aged < 18 years (in The Netherlands, these persons are only allowed to provide a DNA sample with parental <span class="lh">consent), and DNA sampling was postponed until parental consent was obtained or until they had turned 18 years during follow-up.
