Depression and pain: testing of serial multiple mediators

Figures & data

Figure 1 Path diagram illustrating the direct effects and causal paths linking depression–pain symptoms.

Notes: a₁, a₂, a₃, b₁, b₂, b₃, c′ = path coefficient (unstandardized coefficient). The model fit statistics was chi-square =32.292, df=3, P<0.0001, chi-square/df=10.76; comparative fit index =0.941, root mean square error approximation =0.168, and standardized root mean square residual =0.0350.
Abbreviations: df, degrees of freedom; SMM, serial multiple mediation.

Table 1 Participants’ characteristics

Variables	Values, mean ± SD (min–max) OR n (%)
Age; mean ± SD (min–max) (years)	45.61±15.9 (18–83)
Sex, n (%)
Male	82 (23.7)
Female	264 (76.3)
Education, n (%)
Less than elementary	46 (13.1)
Elementary to junior high school	104 (30.1)
High school	79 (22.8)
Bachelor or higher	117 (33.8)
Marital status, n (%)
Single	114 (32.9)
Cohabitated or married	151 (43.6)
Lived alone (widowed/divorced/separated)	81 (23.4)
Employment, n (%)
Yes	264 (76.3)
No	82 (23.7)
Clinical characteristics (mean ± SD)
Pain	49.78 (27.5)
Perceived stress	19.22 (5.3)
MMSE	26.20 (3.3)
Self-sacrificing	8.01 (3.4)
HAMD	24.24 (6.6)

Abbreviations: SD, standard deviation; min, minimum; max, maximum; OR, odds ratio; MMSE, Mini-Mental State Exam; HAMD, Hamilton Depression Rating Scale.

Table 2 Path coefficients, indirect effects, and 95% bias-corrected confidence interval predicting pain symptom scores (N=346)a

Path	Effect	BootLLCI	BootULCI	SE	t	P-value
Total effect (c)	0.9720	0.5375	1.4062	0.2208	4.4009	<0.0001
Direct effect (c′)	0.6222	0.1751	1.0694	0.2273	2.7372	0.0065
a1	−0.0650	−0.1054	−0.0245	0.0206	−3.1574	0.0017
a2	0.2343	0.1543	0.3143	0.0407	5.3559	<0.0001
a3	0.0360	−0.0196	0.0917	0.0283	1.2740	0.2035
b1	−0.7081	−1.8316	0.4153	0.5711	−1.2398	0.2159
b2	1.0373	0.4468	1.6277	0.3002	3.4558	0.0006
b3	0.8021	−0.0571	1.6613	0.4368	1.8363	0.0672
Indirect effects
Total indirect effect	0.3496	0.1830	0.5643	0.0959	3.6455	0.0003
a1b1	0.0460	−0.0133	0.1552	0.0415	1.1084	0.2684
a2b2	0.2430	0.1015	0.4400	0.0845	2.8757	0.0043
a3b3	0.0606	0.0010	0.1736	0.0417	1.4532	0.1471

Notes:

a Models include controls for age, sex, education level, employment status, and income. a₁, a₂, a₃ = regression coefficients of X₁, X₂, X₃, respectively. b₁, b₂, b₃ = regression coefficients of M₁, M₂, M₃, respectively.

Abbreviations: BootLLCI, bootstrapping lower limit confidence interval; BootULCI, bootstrapping upper limit confidence interval; SE, standard error.

Table 3 Possible serial models, according to different causal orders

Mediator by causal order	SMM model
	1	2	3	4	5	6
M1	Perceived stress	Perceived stress	Cognitive function	Cognitive function	Self-sacrificing	Self-sacrificing
M2	Cognitive function	Self-sacrificing	Perceived stress	Self-sacrificing	Perceived stress	Cognitive function
M3	Self-sacrificing	Cognitive function	Self-sacrificing	Perceived stress	Cognitive function	Perceived stress

Abbreviation: SMM, serial multiple mediator.

Table 4 Causal chain according to models (X → M₁ → M₂ → M₃ → Y)

SMM 1
ind1	Depression	Perceived stress	Pain
ind2		Perceived stress	Cognitive function	Pain
ind3		Perceived stress	Self-sacrificing	Pain
ind4		Perceived stress	Cognitive function	Self-sacrificing	pain
ind5		Cognitive function	Pain
ind6		Cognitive function	Self-sacrificing	Pain
ind7		Self-sacrificing	Pain
SMM 2
ind1	Depression	Perceived stress	Pain
ind2		Perceived stress	Self-sacrificing	Pain
ind3		Perceived stress	Cognitive function	Pain
ind4		Perceived stress	Self-sacrificing	Cognitive function	Pain
ind5		Self-sacrificing	Pain
ind6		Self-sacrificing	Cognitive function	Pain
ind7		Cognitive function	Pain
SMM 3
ind1	Depression	Cognitive function	Pain
ind2		Cognitive function	Perceived stress	Pain
ind3		Cognitive function	Self-sacrificing	Pain
ind4		Cognitive function	Perceived stress	Self-sacrificing	Pain
ind5		Perceived stress	Pain
ind6		Perceived stress	Self-sacrificing	Pain
ind7		Self-sacrificing	Pain
SMM 4
ind1	Depression	Cognitive function	Pain
ind2		Cognitive function	Self-sacrificing	Pain
ind3		Cognitive function	Perceived stress	Pain
ind4		Cognitive function	Self-sacrificing	Perceived stress	Pain
ind5		Self-sacrificing	Pain
ind6		Self-sacrificing	Perceived stress	Pain
ind7		Perceived stress	Pain
SMM 5
ind1	Depression	Self-sacrificing	Pain
ind2		Self-sacrificing	Perceived stress	Pain
ind3		Self-sacrificing	Cognitive function	Pain
ind4		Self-sacrificing	Perceived stress	Cognitive function	Pain
ind5		Perceived stress	Pain
ind6		Perceived stress	Cognitive function	Pain
ind7		Cognitive function	Pain
SMM 6
ind1	Depression	Self-sacrificing	Pain
ind2		Self-sacrificing	Cognitive function	Pain
ind3		Self-sacrificing	Perceived stress	Pain
ind4		Self-sacrificing	Cognitive function	Perceived stress	Pain
ind5		Cognitive function	Pain
ind6		Cognitive function	Perceived stress	Pain
ind7		Perceived stress	Pain

Note: Values in bold indicate significant bias-corrected bootstrap 95% confidence interval above zero.

Abbreviations: Ind, indirect path; SMM, serial multiple mediator.

Figure 2 Path diagram illustrating direct effects and causal paths linking depression with pain symptoms (SMM 3).

Notes: Values outside parentheses = path coefficient or unstandardized coefficient; values in parentheses = standard error, *P<0.001. The model fit statistics were as follows: chi-square =1.300, df=1, chi-square/df=1.3, P=0.254; comparative fit index =0.999, and root mean square error approximation =0.029.
Abbreviations: df, degrees of freedom; SMM, serial multiple mediation.

Figure 3 An alternative serial mediation model proposing how self-sacrificing predicts pain.

Notes: Values outside parentheses = path coefficient or unstandardized coefficient; values in parentheses = standard error, *P<0.001. The model fit statistics were as follows: chi-square =1.300, df=1, chi-square/df=1.3, P=0.254; comparative fit index =0.999, and root mean square error approximation =0.029.
Abbreviation: df, degrees of freedom.