Table 2. Socio-demographic and medical characteristics at baseline.

	Study population (N = 325) Mean (SD) Number (%)	N missing (%)
Age (range 19-70)	46.5 (12.3)	0 (0%)
Female gender	244 (75.1%)	0 (0%)
Nationality		0 (0%)
Dutch	279 (85.8%)
Other	46 (14.2%)
Education level		0 (0%)
Lower education	109 (33.5%)
Intermediate education	126 (38.8%)
Higher education	90 (27.7%)
Work status		0 (0%)
Employed	187 (57.5%)
Unemployed	26 (8.0%)
Long term sick leave	93 (28.6%)
Retired	19 (5.8%)
Marital status		0 (0%)
Married or cohabiting	199 (61.2%)
Unmarried	85 (26.2%)
Divorced	30 (9.2%)
Widow	11 (3.4%)
Number of self-reported somatic comorbidities		2 (0.6%)
None	81 (24.9%)
1	91 (28.2%)
2	70 (21.7%)
≥3	81 (25.1%)
Symptom severity (PHQ-15 score, scale 0-30)	12.3 (5.3)	0 (0%)
Physical and mental functioning* (RAND-36 score, scale 0-100)
Mental Component Score (MCS)	52.2 (20.3)	2 (0.6%)
Physical Component Score (PCS)	47.3 (20.0)	2 (0.6%)
Symptom Focusing (CBRQ Symptom Focusing score, scale 0-24)	10.6 (5.2)	0 (0%)
Somatosensory amplification scale (SSAS, scale 10-50)	27.2 (6.2)	1 (0.3%)

^*in earlier publications of the PROSPECTS study, the calculation of MCS and PCS was based on version 1.0 of the RAND-36 questionnaire, resulting in small

differences in reported MCS and PCS. Correlations between both calculations (RAND-36 version 1.0 and 2.0) were high (Pearson’s r 0.99 for both MCS and PCS)