Patient-reported depression severity and cognitive symptoms as determinants of functioning in patients with major depressive disorder: a secondary analysis of the 2-year prospective PERFORM study

Figures & data

Figure 1 Illustration of the (A) saturated structural equation model (SEM) and (B) G-computation model.

Notes: (A) The SEM estimates all regression coefficients between 5-item Perceived Deficit Questionnaire (PDQ-5) score, Sheehan Disability Scale (SDS) total score, and 9-item Patient Health Questionnaire (PHQ-9) score at subsequent visits (solid one-headed arrows), as well as variances and covariances between PDQ-5 score, SDS total score, and PHQ-9 score at the same visits (dotted double-headed arrows), in a single analysis. (B) In the G-computation of the causal effect of PDQ-5 score at Month 2 on SDS total score at Month 6 (example highlighted in gray box), SDS total score and PHQ-9 score at Month 2 are potential confounders and are therefore accounted for, whereas PDQ-5 and PHQ-9 scores at Month 6 are mediating variables and are therefore not accounted for.

Table 1 Summary statistics of PDQ-5 score, SDS total score, and PHQ-9 score by visit

Variable		Baseline	Month 2	Month 6	Month 12	Month 18	Month 24
PDQ-5	N	770	714	644	654	580	564
	Mean (SD)	11.38 (4.57)	10.32 (4.77)	9.03 (5.08)	8.23 (5.18)	8.03 (5.23)	7.81 (5.19)
	Median [Q1, Q3]	12 [8, 15]	11 [7, 14]	5 [5, 13]	8 [4, 12]	8 [4, 12]	8 [3, 12]
SDS total	N	750	607	586	554	486	458
	Mean (SD)	19.19 (6.76)	14.71 (7.94)	11.86 (8.67)	10.30 (8.20)	9.91 (8.51)	9.25 (8.13)
	Median [Q1, Q3]	20 [15, 24]	15 [9, 21]	12 [4, 18]	9 [3, 16]	8 [2, 16]	7.5 [2, 15]
PHQ-9	N	940	805	740	701	638	604
	Mean (SD)	17.61 (5.31)	12.73 (6.24)	10.76 (6.65)	9.85 (6.79)	9.62 (6.86)	9.11 (6.60)
	Median [Q1, Q3]	18 [14, 22]	13 [8, 17]	10 [5, 15]	9 [4, 14]	9 [4, 14]	8 [4, 13]

Abbreviations: PDQ-5, 5-item Perceived Deficit Questionnaire; PHQ-9, 9-item Patient Health Questionnaire; SD, standard deviation; SDS, Sheehan Disability Scale; Q, quartile.

Figure 2 Distribution of depression severity (9-item Patient Health Questionnaire [PHQ-9] score, range 0–27), functional impairment (Sheehan Disability Scale [SDS] total score, range 0–30) and cognitive symptoms (5-item Perceived Deficit Questionnaire [PDQ-5] score, range 0–20) by visit.

Note: Higher scores indicate worse outcomes.

Figure 3 Significant regression coefficients based on the structural equation model standardized by time point.

Note: Only effects that were significant at the P<0.001 level are shown; the thickness of the arrows is proportional to the effect estimates.
Abbreviations: PDQ-5, 5-item Perceived Deficit Questionnaire; PHQ-9, 9-item Patient Health Questionnaire; SDS, Sheehan Disability Scale.

Figure 4 Causal effect sizes from G-computation standardized by time point.

Note: Effects that were significant at the P<0.001 level are shown in black, and effects that were significant at the P<0.05 level (but not at the 0.001 level) are shown in gray; the thickness of the arrows is proportional to the effect estimates.
Abbreviations: PDQ-5, 5-item Perceived Deficit Questionnaire; PHQ-9, 9-item Patient Health Questionnaire; SDS, Sheehan Disability Scale.

Data availability

The authors declare that the data supporting the findings of this study are available within the article. The authors may be contacted for further data sharing.