Table 1.

Study design, visits, and data collection.

		Study phase
		Baseline	Mobile DOTa			Observation		Off study
Study visit		No visit	1	2	3	4	5	Withdraw
Study day		−180 to 1	0	30-136	165-211	240- 316	345- 391	Anytime
Data collection
	Demographic data		x
	Hydroxyurea dose (mg/kg/d)	x	x	x	x	x	x	x
	Pharmacy list		x	x	x	x	x	x
	Medication possession ratiob	x			x		x	x
	Phone numbers		x	x	x	x	x	x
	Morisky Medication Adherence Scale, 4-item		x	x	x	x	x	x
	Satisfaction survey			x	x			x
	Newest vital signc		x		x		x	x
	Transition Readiness Assessment Questionnaire 5.0c		x		x		x	x
	Laboratory data		x	x	x	x	x	x
	Urine assay		x	x	x	x	x	x
	Indication for withdraw							x

^aMobile DOT: Mobile Directly Observed Therapy.

^bMedication possession ratio is calculated for each study phase and calculated after participants complete the study.

^cOnly for adolescent participants (those who are 16- to 19-years old) at enrollment.