3. Domain‐specific risk of bias per outcome.

	QUIPS domains
	Selection bias			Attrition bias			PF measurement bias			Outcome measurement bias			Confounding bias			Statistical analysis bias
	Low	Moderate	High	Low	Moderate	High	Low	Moderate	High	Low	Moderate	High	Low	Moderate	High	Low	Moderate	High
ICU admission	30	14	3	20	20	7	26	12	9	41	6	0	28	11	8	36	6	5
Hospitalisation	22	8	3	15	13	5	15	7	11	30	3	0	22	8	3	23	7	3
Length of ICU admission	0	2	0	2	0	0	2	0	0	1	1	0	1	1	0	1	1	0
Length of hospitalisation	3	1	1	3	2	0	3	2	0	5	0	0	2	1	2	3	2	0
Length of mechanical ventilation	1	0	0	1	0	0	0	1	0	1	0	0	0	1	0	1	0	0
Mechanical ventilation	37	10	3	24	20	6	26	13	11	41	9	0	28	12	10	39	7	4
Mortality	76	26	11	66	35	12	67	22	24	108	3	2	69	26	18	75	23	15
Pneumonia	4	2	0	3	2	1	2	3	1	4	1	1	3	1	2	3	2	1
Severe COVID	19	12	0	16	11	4	20	3	8	22	6	3	17	8	6	21	5	5
Total	192	75	21	150	103	35	161	63	64	253	29	6	170	69	49	202	53	33

ICU: Intensive care unit
PF: Prognostic factor
QUIPS: Quality in Prognostic Studies tool