29. Risk of bias.

	Study design	Low risk of bias		Unclear risk of bias		High risk of bias
		n	Row %	n	Row %	n	Row %	n total
Effectiveness studies	RCT/CCT	3	100%					3
	Case‐control	8	57.1%	4	28.6%	2	14.3%	14
	Prospective/retrospective cohort	4	13.0%	21	67.7%	6	19.4%	31
	Case‐only ecological method			2	66.7%	1	33.3%	3
	Subtotal	15	29.4%	27	53.0%	9	17.6%	51
	Study design	Low risk of bias		Unclear risk of bias		High risk of bias
		n	Row %	n	Row %	n	Row %	n total
Safety studies	RCT/CCT	2	28.6%	2	28.6%	3	42.9%	7
	Case‐control	8	38.1%	11	52.4%	2	9.5%	21
	Prospective/retrospective cohort	14	43.8%	4	12.5%	14	43.8%	32
	Self‐controlled case series/person‐time cohort	11	68.8%	5	31.2%			16
	Case cross‐over	1	33.3%	2	66.7%			3
	Case‐only ecological method	2	25.0%	4	50.0%	2	25.0%	8
	Subtotal	38	43.7%	28	32.2%	21	24.1%	87
Total (all studies)		53	38.4%	55	39.9%	30	21.7%	138
	Study design	Low risk of bias		Unclear risk of bias		High risk of bias
		n	Row %	n	Row %	n	Row %	n total
Safety studies (excluding short‐term side effects studies)	Case‐control	8	38%	11	52%	2	10%	21
	Prospective/retrospective cohort	14	64%	4	18%	4	18%	22
	Self‐controlled case series/person‐time cohort	11	69%	5	31%			16
	Case cross‐over	1	33%	2	67%			3
	Case‐only ecological method	2	25%	4	50%	2	25%	8
	Total	36	51%	26	37%	8	11%	70

CCT: controlled clinical trial
RCT: randomised controlled trial