The eligibility criteria for trial participants.
The flexibility with which the experimental intervention is applied.
The degree of practitioner expertise in applying and monitoring the experimental intervention.
The flexibility with which the comparison intervention is applied.
The degree of practitioner expertise in applying and monitoring the comparison intervention.
The intensity of follow-up of trial participants.
The nature of the trial's primary outcome.
The intensity of measuring participants' compliance with the prescribed intervention, and whether compliance-improving strategies are used.
The intensity of measuring practitioners' adherence to the study protocol, and whether adherence-improving strategies are used.
The specification and scope of the analysis of the primary outcome.