2. Descriptive summary of included studies.

Study variables		All included studies (n = 60)		Synthesis studies (n = 52)
		n	%	n	%
Year published	Older (before 2013)	44	73.3%	37	71.2%
	Recent (2013 ‐ 2018)	16	26.7%	16	30.8%
Sample size (median, IQR)		257	132 ‐ 592	312	166 ‐ 627
Population source	Healthcare	37	61.7%	33	63.5%
	Occupational	16	26.2%	14	26.4%
	General	3	4.9%	3	5.7%
	Mixed	3	4.9%	1	1.9%
	Not specified	1	1.6%	1	1.9%
Duration of LBP	Acute	5	8.2%	4	7.5%
	Subacute	5	8.2%	5	9.4%
	Chronic	22	36.7%	20	38.5%
	Mixed	19	31.1%	14	26.4%
	Not specified	9	14.8%	9	17.0%
Type of expectations measure	General expectations	42	68.9%	36	67.9%
	Self‐efficacy expectations	12	19.7%	12	22.6%
	Treatment expectations	17	28.3%	14	26.9%
Number of expectations measures	1	44	73.3%	39	75.0%
	2	13	21.3%	11	20.8%
	3	2	3.3%	2	3.8%
	4	1	1.6%	0	0.0%
Prognostic factor study phase	Exploratory/TEM	3	5.0%	3	5.8%
	Exploratory	44	73.3%	37	71.2%
	Confirmatory	13	21.3%	12	22.6%
Outcomes assessed	Pain	31	51.7%	24	46.2%
	Functional limitations	36	60.0%	30	57.7%
	Work participation	35	58.3%	31	59.6%
	Satisfaction	5	8.3%	2	3.8%
	Global improvement	9	15.0%	8	15.4%
	Health‐related quality of life	6	10.0%	4	7.7%
	Cost	7	11.5%	6	11.3%
	Mood	3	4.9%	3	5.7%
Follow‐up times available	Short (3 ‐ 4 months)	29	48.3%	24	46.2%
	Moderate (5 ‐ 8 closest to 6 months)	16	26.2%	13	24.5%
	Long (8 ‐ 16 closest to 12 months)	40	65.6%	35	66.0%
	Very long (> 16 months)	7	11.5%	7	13.2%
Low risk of bias by QUIPS domain	Study Participation	18	30.0%	17	32.7%
	Study Attrition	36	60.0%	33	63.5%
	Prognostic Factor Measurement	27	45.0%	24	46.2%
	Outcome Measurement	54	90.0%	46	88.5%
	Study Confounding	28	46.7%	27	51.9%
	Statistical Analyses & Reporting	41	68.3%	38	73.1%
All QUIPS ROB domains rated low or moderate		36	60.0%	34	65.4%
All QUIPS ROB domains rated low		2	3.3%	2	3.8%

LBP = low back pain; ROB = risk of bias; TEM = treatment effect modification; QUIPS = Quality in Prognosis Studies Tool