Psychometric validation of the Perceived Deficits Questionnaire-Depression (PDQ-D) instrument in US and UK respondents with major depressive disorder

Figures & data

Figure 1 Study design and selection of participants, including initial target for number of respondents.

Abbreviations: BL, baseline; LEAPS, modified Lam Employment Absence and Productivity Scale; MDD, major depressive disorder; MOS COG-R, Medical Outcomes Study Cognitive Functioning Scale-Revised-acute form; PDQ-D, Perceived Deficits Questionnaire-Depression; PGI-S, Patient Global Impression of Severity scale; PHQ-9, Patient Health Questionnaire-9; SDS, Sheehan Disability Scale; WPAI, Work Productivity and Activity Impairment Questionnaire.

Figure 2 Subject disposition.

Abbreviation: MDD, major depressive disorder.

Table 1 Comparison of baseline demographic characteristics and baseline patient-reported scores for US and UK MDD samples

Characteristic	US MDD (n=206)		UK MDD (n=215)		Difference (US–UK)
	N	Mean (SD)	N	Mean (SD)
Female sex (%)a	133	64.6	156	72.6	−8.0
Age, years	206	50.8 (14.2)	215	46.9 (13.9)	3.9
Educational status (%)a
Less than high school	206	5.8	–	–	–
High school	206	35.9	–	–	–
Some college	206	30.6	–	–	–
Bachelor’s degree or higher	206	27.7	–	–	–
≤5 grade C GCSEs (or equivalent)	–	–	215	29.8	–
>5 grade C GCSEs (or equivalent)	–	–	215	9.3	–
Advanced school/college qualificationsb	–	–	215	27.9	–
Undergraduate degree or equivalent	–	–	215	13.5	–
Postgraduate degree or equivalent	–	–	215	7.0	–
Professional qualification	–	–	215	12.6	–
PDQ-D
Total score	186	37.7 (19.4)	191	42.1 (18.3)	−4.4
Attention/concentration	198	10.6 (5.3)	208	11.7 (4.8)	−1.2
Retrospective memory	199	9.1 (5.6)	204	10.0 (5.5)	−0.9
Prospective memory	199	7.6 (4.7)	209	8.7 (4.8)	−1.2
Planning/organization	198	10.4 (5.3)	202	11.4 (5.0)	−0.9
PHQ-9 Total score	206	15.7 (4.9)	215	16.6 (5.0)	−0.9
MOS COG-R Total score	205	35.0 (12.6)	215	31.5 (12.4)	3.5
SDS Total score	206	16.0 (8.1)	215	18.7 (7.7)	−2.8
WPAI:SHP score
Absenteeism	92	5.7 (14.4)	77	9.2 (20.7)	−3.5
Presenteeism	91	33.7 (26.0)	75	49.3 (21.1)	−15.6
Overall work impairment	91	36.5 (27.7)	77	53.1 (24.1)	−16.6
Activity impairment	204	58.8 (26.3)	215	64.3 (24.9)	−5.5
LEAPS Total score
Total score	182	9.4 (8.3)	195	12.0 (9.1)	−2.6
Productivity	186	3.3 (3.6)	200	4.6 (4.0)	−1.3
PGI-Severity score	204	3.6 (1.5)	214	3.8 (1.5)	−0.2

Notes:

a Percentage of respondents is presented;

b Advanced or Advanced Subsidiary levels/Scottish Highers/National Vocational Qualification levels 3 and 4. “–” indicates not applicable.

Abbreviations: GCSE, General Certificate of Secondary Education; LEAPS, modified Lam Employment Absence and Productivity Scale; MDD, major depressive disorder; MOS COG-R, Medical Outcomes Study Cognitive Functioning Scale-Revised-acute form; PDQ-D, Perceived Deficits Questionnaire-Depression; PGI-Severity, Patient Global Impression of Severity scale; PHQ-9, Patient Health Questionnaire-9; SDS, Sheehan Disability Scale; WPAI:SHP, Work Productivity and Activity Impairment Questionnaire: Specific-Health Problem.

Table 2 Response frequency distributions and descriptive statistics for PDQ-D items at baseline

Subscale	Item no	US MDD sample					UK MDD sample
		N	Missing (%)	Mean score (SD)	Percentage of responders		N	Missing (%)	Mean score (SD)	Percentage of responders
					“Never”	“Very often”				“Never”	“Very often”
Attention/concentration	1	204	1.0	3.17 (1.29)	9.7	21.5	215	0.0	3.36 (1.25)	6.3	25.7
	5	202	1.9	3.06 (1.32)	14.5	18.3	215	0.0	3.41 (1.21)	7.9	22.5
	9	202	1.9	3.05 (1.32)	15.6	17.2	213	0.9	3.39 (1.22)	7.3	22.5
	13	205	0.5	3.62 (1.26)	8.1	32.3	212	1.4	3.98 (1.11)	2.6	44.0
	17	205	0.5	2.63 (1.42)	28.0	16.1	213	0.9	2.60 (1.34)	27.2	11.0
Retrospective memory	2	205	0.5	2.92 (1.39)	21.0	18.8	212	1.4	3.02 (1.37)	18.3	17.8
	6	201	2.4	2.74 (1.20)	15.1	9.7	213	0.9	2.94 (1.24)	14.1	12.0
	10	202	1.9	2.81 (1.39)	22.0	16.1	214	0.5	3.14 (1.35)	16.2	19.9
	14	203	1.5	2.70 (1.43)	28.5	17.2	211	1.9	2.81 (1.42)	26.2	16.2
	18	205	0.5	3.05 (1.34)	14.0	19.9	213	0.9	3.14 (1.28)	11.5	18.3
Prospective memory	3	203	1.5	3.21 (1.30)	10.8	22.0	215	0.0	3.53 (1.20)	5.8	25.7
	7	202	1.9	2.09 (1.21)	41.9	5.9	212	1.4	2.24 (1.29)	39.8	8.4
	11	204	1.0	3.02 (1.29)	11.3	19.4	213	0.9	3.33 (1.26)	8.4	22.5
	15	205	0.5	2.04 (1.19)	43.5	5.4	214	0.5	2.42 (1.27)	29.3	8.9
	19	205	0.5	2.28 (1.22)	34.9	5.9	214	0.5	2.27 (1.26)	36.6	7.3
Planning/organization	4	203	1.5	3.23 (1.36)	14.5	25.3	213	0.9	3.34 (1.19)	6.8	21.5
	8	202	1.9	2.79 (1.37)	22.0	16.7	211	1.9	3.04 (1.30)	15.2	16.2
	12	205	0.5	3.63 (1.25)	8.1	30.1	214	0.5	3.87 (1.14)	3.7	38.7
	16	204	1.0	2.78 (1.30)	18.8	12.9	211	1.9	3.07 (1.32)	14.1	18.3
	20	204	1.9	2.91 (1.32)	18.3	15.6	212	1.4	3.23 (1.35)	13.6	23.0

Abbreviations: MDD, major depressive disorder; PDQ-D, Perceived Deficits Questionnaire-Depression.

Table 3 Internal consistency reliability: PDQ-D scale-level properties at baseline for US and UK MDD samples

Measure	n	Mean	Median	SD	Floor (%)	Ceiling (%)	Cronbach’s alpha	Average inter-item correlation
US MDD sample (N=206)
Total score	186	37.7	37.5	19.4	2.2	1.1	0.96	0.53
Attention/concentration	198	10.6	11.0	5.3	2.5	4.0	0.86	0.54
Retrospective memory	199	9.1	9.0	5.6	4.5	3.0	0.89	0.64
Prospective memory	199	7.6	7.0	4.7	4.0	1.5	0.81	0.47
Planning/organization	198	10.4	10.5	5.3	3.0	3.0	0.86	0.56
UK MDD sample (N=215)
Total score	191	42.1	43.0	18.3	0.5	1.0	0.95	0.50
Attention/concentration	208	11.7	11.0	4.8	0.5	5.8	0.84	0.53
Retrospective memory	204	10.0	10.0	5.5	2.9	3.9	0.89	0.62
Prospective memory	209	8.7	9.0	4.8	1.4	1.4	0.81	0.47
Planning/organization	202	11.4	11.5	5.0	0.5	6.4	0.84	0.53

Abbreviations: MDD, major depressive disorder; PDQ-D, Perceived Deficits Questionnaire-Depression.

Table 4 Convergent validity: Pearson correlation coefficients between baseline PDQ-D subscale and total scores and baseline scores from other survey measures in the US and UK study populations with MDD

Scale	Measure	Pearson correlation at baseline
		PDQ-D Total score	Attention	Retrospective memory	Prospective memory	Planning
US MDD sample
PHQ-9	Total score	0.54	0.51	0.45	0.44	0.48
MOS COG-R	Total score	−0.78	−0.72	−0.69	−0.70	−0.71
SDS	Total score	0.32	0.28	0.22	0.33	0.35
WPAI:SHP	Absenteeism	0.06	0.04	0.00	0.04	0.08
	Presenteeism	0.34	0.27	0.22	0.33	0.37
	Overall work impairment	0.33	0.26	0.21	0.31	0.35
	Activity impairment	0.32	0.28	0.23	0.32	0.34
LEAPS	Total score	0.38	0.35	0.30	0.33	0.38
	Productivity	0.37	0.33	0.29	0.33	0.35
PGI-Severity	Score	0.31	0.28	0.20	0.26	0.37
UK MDD sample
PHQ-9	Total score	0.62	0.55	0.51	0.52	0.60
MOS COG-R	Total score	−0.80	−0.76	−0.69	−0.71	−0.74
SDS	Total score	0.53	0.47	0.43	0.47	0.55
WPAI:SHP	Absenteeism	0.05	−0.01	0.10	0.07	0.03
	Presenteeism	0.47	0.46	0.46	0.46	0.36
	Overall work impairment	0.41	0.38	0.42	0.41	0.32
	Activity impairment	0.53	0.47	0.44	0.43	0.59
LEAPS	Total score	0.51	0.48	0.40	0.49	0.48
	Productivity	0.52	0.46	0.41	0.49	0.49
PGI-Severity	Score	0.43	0.39	0.34	0.30	0.48

Abbreviations: LEAPS, modified Lam Employment Absence and Productivity Scale; MDD, major depressive disorder; MOS COG-R, Medical Outcomes Study Cognitive Functioning Scale-Revised-acute form; PDQ-D, Perceived Deficits Questionnaire-Depression; PGI-Severity, Patient Global Impression of Severity scale; PHQ-9, Patient Health Questionnaire-9; SDS, Sheehan Disability Scale; WPAI:SHP, Work Productivity and Activity Impairment Questionnaire: Specific-Health Problem.

Table 5 Mean comparison across MDD and general populations for testing known-groups validity of baseline PDQ-D total and subscale scores

	MDD samples			General population sample			Mean difference	da
	N	Estimated mean	SEM	N	Estimated mean	SEM
US sample
Total score	186	37.6	1.22	198	11.5	1.19	26.1	1.56
Attention/concentration	198	10.5	0.34	203	3.4	0.33	7.1	1.50
Retrospective memory	199	9.0	0.34	205	2.7	0.33	6.3	1.33
Prospective memory	199	7.5	0.28	207	2.5	0.27	5.0	1.28
Planning/organization	198	10.4	0.32	205	2.7	0.32	7.7	1.69
UK sample
Total score	191	41.9	1.28	199	17.1	1.25	24.7	1.40
Attention/concentration	208	11.7	0.33	209	4.9	0.32	6.8	1.44
Retrospective memory	204	10.0	0.35	216	3.9	0.34	6.1	1.23
Prospective memory	209	8.7	0.30	218	3.8	0.29	4.9	1.13
Planning/organization	202	11.3	0.34	213	4.2	0.33	7.0	1.48

Note:

a Cohen’s d effect size for differences among estimated means calculated from the ANCOVA model.

Abbreviations: ANCOVA, analysis of covariance; MDD, major depressive disorder; PDQ-D, Perceived Deficits Questionnaire-Depression; SEM, standard error of the mean.

Figure 3 Known-groups validity: mean baseline PDQ-D subscale and total scores for the MDD and general populations: (A) US sample; (B) UK sample. ^*P<0.001 vs general population sample.

Abbreviations: MDD, major depressive disorder; PDQ-D, Perceived Deficits Questionnaire-Depression.

Table 6 Responsiveness to change: Comparison of mean changes from baseline in PDQ-D subscale and total scores for respondents with MDD as a function of their classification based on worsening, no change, or improvement from baseline to follow-up in PHQ-9 score

Measure	Worseneda			No changea			Improveda			P-valueb
	n	Estimated mean	SEM	n	Estimated mean	SEM	n	Estimated mean	SEM
US MDD sample
Total score	15	1.6*	3.19	83	−2.7*	1.35	49	−10.5#	1.76	0.0004
Attention/concentration	16	0.6*	0.96	87	−0.8*	0.41	55	−2.5#	0.51	0.0049
Retrospective memory	17	0.4*	0.95	88	−0.7*	0.42	56	−2.6#	0.52	0.0039
Prospective memory	17	0.5*	0.75	87	−0.3*	0.33	56	−1.8#	0.41	0.0045
Planning/organization	16	0.4*	0.95	86	−1.1*	0.41	56	−3.4#	0.50	0.0001
UK MDD sample
Total score	19	−1.4	3.52	85	−5.4	1.67	22	−12.0	3.28	0.0798
Attention/concentration	22	0.6*	0.91	99	−1.4*,#	0.43	24	−3.1#	0.87	0.0148
Retrospective memory	23	0.3*	0.96	94	−1.5*,#	0.47	23	−3.1#	0.96	0.0499
Prospective memory	23	−0.7	0.85	97	−1.1	0.41	24	−2.2	0.83	0.3823
Planning/organization	22	0.3*	0.94	94	−1.7*,#	0.45	23	−3.7#	0.92	0.0111

Notes:

*,# Estimated means within a row with different superscripts (* or #) are significantly different (P<0.05) based on post hoc paired comparison using Bonferroni’s correction for multiple comparisons.

a “Improved” respondents’ baseline PHQ-9 score exceeded follow-up score by ≥5 points; “No change” respondents’ PHQ-9 scores at baseline and follow-up were within 5 points of each other (in either direction); “Worsened” respondents’ follow-up PHQ-9 score exceeded baseline score by ≥5 points.

b Difference in estimated mean PDQ-D scores across PHQ-9 categories.

Abbreviations: MDD, major depressive disorder; PDQ-D, Perceived Deficits Questionnaire-Depression; PHQ-9, Patient Health Questionnaire-9; SEM, standard error of the mean.