Psychiatric comorbidity as predictor of costs in back pain patients undergoing disc surgery: a longitudinal observational study

Table 4 Predictors of direct, indirect and total costs including monetarily valued informal care and reduced productivity at work

Parameter	Direct costs	Standard error		Indirect costs	Standard error		Total costs	Standard error
Constant	6,388	869	***	6,915	635	***	13,269	1,176	***
Diagnosis	381	158	*	−28	205		371	277
Psychiatric comorbidity	893	352	*	448	327		1,348	549	*
T1	−2,450	166	***	994	201	***	−1,453	283	***
T1 x psychiatric comorbidity	−564	454		−688	499		−1,242	755
T2	−5,063	192	***	−3,112	282	***	−8,167	368	***
T2 x psychiatric comorbidity	38	709		1,646	762	*	1,643	1,133
Chronic medical disease	643	191	***	811	229	***	1,397	329	***
Number of previous disc surgeries	548	162	***	1,197	147	**	1,755	232	***
Age (centralized to mean)	−9.50	10.30		67	12.40	***	58	17.69	**
Gender (ref: female)	−871	158	***	2,237	167	***	1,343	247	***
Being married	104	181		499	262		594	354
ISCED educational level 3 (ref ≤ 2)	−484	711		256	521		−209	972
ISCED educational level 5 (ref ≤ 2)	−681	729		−160	550		−829	1,009
Living situation: with partner (ref: alone)	−212	269		−100	337		−260	470
Living situation: others (ref: alone)	580	646		689	929		1,333	1,233
Number of children	87	79		−328	90	***	−235	130
Private health insurance (ref: statutory health insurance)	−40	165		−740	255	**	−775	326	*
Being not employed (ref: being employed)	691	269	*	−7,025	323	***	−6,347	462	***
Model statistics
R2 within	0.48			0.46			0.53
R2 between	0.33			0.52			0.35
R2 overall	0.41			0.48			0.43

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