To your point, it's more about subjectivity and perhaps bias of the reviewer than it is an actual placebo effect in the patient... who, in the case of Rett, are likely unaware they're receiving a drug/placebo. Also, the reviewers may be hearing biased comments from the caregiver/parent during the evaluation.
Biomarker data will bring objectivity into the evaluation (e.g. gaba & glutamate), as well as QOL improvements, including sleep and reduction in seizure frequency.