Longitudinal data will be used to follow the natural (non-interventional) course of the disease and the quality of the data. Test-retest reliability will be assessed using diary data from Day 1 to Day 14 in stable subjects as measured by the PIC for the child-completed measure and the CIC for the caregiver measure. Convergent validity (correlations between the ItchRO and similar concepts on the other measures included in the study) will also be explored (such as the correlation between sleep and morning ItchRO diary scores). Clinical validity (correlation between the ItchRO and clinician reports) and preliminary responsiveness of those who changed in their itching status over the two week period will also be assessed if sample sizes allow.