1. Overview of study populations.

Characteristic	Intervention(s) and comparator(s)	Sample sizea	Screened/eligible [N]	Randomised [N]	ITT [N]	Finishing study [N]	Randomised finishing study [%]	Follow‐up
(1) Barczynski 2012	I: total thyroidectomy	(1) To detect an estimated absolute difference in the rate of recurrent hyperthyroidism of 5%, it was calculated that 71 participants would be required in each treatment arm to give the study a power of 80% (2) To detect an estimated difference in ophthalmopathy progression rate of 8%, 83 participants were required in each treatment arm to give the study a power of 80% Anticipating a 15% loss to follow‐up, a total of 200 participants were included	298	100	100	95	95.0	5 years
	C: bilateral subtotal thyroidectomy			100	100	96	96.0
	total:			200	200	191	95.5
(2) Witte 2000	I: total thyroidectomy	‐	‐	50	50	‐	‐	6‐36 (58) months
	C1: bilateral subtotal thyroidectomyb			50	50	‐	‐
	C2: Dunhill procedureb			50	50	‐	‐
	total:			150	150	‐	‐
(3) Chi 2005	I: bilateral subtotal thyroidectomy	‐	‐	166	‐	166	100	3‐26.4 months
	C: Dunhill procedure			174	‐	174	100
	total:			340		340	100
(4) Jarhult 2005	I: total thyroidectomy	‐	‐	22	‐	21	100	3 years
	C: subtotal thyroidectomy			22	‐	21	95.5
	total:			44		43	97.7
(5) Muller 2001	I: bilateral subtotal thyroidectomy	‐	‐	67	‐	46	68.7	6 years
	C: Dunhill procedure			85	‐	53	62.4
	total:			152	‐	99	65.1
Grand total	All interventions			405		368
	All comparators			481		344
	All interventions and comparators			886		712

^aAccording to power calculation in study publication or report.
 ^bSubtotal thyroid resection was performed in 103 patients with an attempt to leave less than 4 mL total remnant

"‐" denotes not reported.

C: comparator; I: intervention; ITT: intention‐to‐treat; N/A: not applicable.