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

Abstract

Background

Although depression and cognitive dysfunction are connected, limited tools exist to capture the patient’s perspective on cognitive dysfunction and its impact on major depressive disorder (MDD). We report results of a psychometric validation of the Perceived Deficits Questionnaire-Depression (PDQ-D), a self-report measure of cognitive dysfunction for use in MDD.

Methods

A non-interventional, prospective, panel-recruited, online survey was conducted using the PDQ-D in adults with and without MDD in the US and UK. Respondents were assessed at baseline and after 6 weeks (MDD only) (baseline: US n=418, UK n=437, 49% MDD; follow-up: US n=169, UK n=153, all MDD). The criterion measures included: Medical Outcomes Study Cognitive Functioning Scale-Revised-acute form (MOS COG-R), Patient Health Questionnaire-9 (PHQ-9), Patient Global Impression of Severity scale (PGI-Severity), Sheehan Disability Scale (SDS), Work Productivity and Activity Impairment Questionnaire: Specific-Health Problem (WPAI:SHP), and modified Lam Employment Absence and Productivity Scale (LEAPS). US and UK data were analyzed separately.

Results

Internal consistency was high for PDQ-D total scale and four subscales (Cronbach’s alpha 0.81–0.96). Convergent validity was good, with strong concordance with MOS COG-R and moderate/small correlations with PHQ-9, SDS, WPAI:SHP, LEAPS, and PGI-Severity. Significant differences (all P<0.001) existed for all PDQ-D subscale and total scores between MDD/non-MDD samples. The PDQ-D was responsive to changes in depression symptom severity. Confirmatory factor analysis supported scoring of a global overall scale for perceived cognitive dysfunction.

Conclusion

The PDQ-D provides a reliable and valid measure of subjective cognitive dysfunction in patients with MDD.

Keywords:

• major depressive disorder
• cognitive dysfunction
• psychometric validation
• self-report

Supplementary materials

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

Background information on methods

Respondents/sample

The US and UK samples were provided by KnowledgePanel^® (GfK Custom Research, LLC, USA) and MrOps (London, UK), respectively. KnowledgePanel^® has been in continuous use in the US since 1998 and comprises more than 50,000 adult members recruited using a combination of random-digit-dial telephone and address-based sampling selected from the US Postal Service Computerized Delivery Sequence File. Profile information, with questions on health topics including depression, is collected and updated on an annual basis. MrOps is a specialist company with access to over 40 screened and validated sample sources worldwide, many of which are online panels.

Ethics approval

Data were collected by survey companies through their existing approved market-research panels, following their own procedures. When subjects are enrolled in such panels, they provide the panel owners with written informed consent, and agree to be contacted for participation in online surveys. For this survey, we ensured that the participants signed an additional informed consent form to participate.

In the US, this type of survey is exempt from Institutional Review Board approval according to guidelines from the US Office for Human Research Protections which stipulate that research involving the use of educational tests (cognitive, diagnostic, aptitude, achievement), survey procedures, interview procedures or observation of public behavior, are exempt unless:

1. Information obtained is recorded in such a manner that human subjects can be identified, directly or through identifiers linked to the subjects; and

2. Any disclosure of the human subjects’ responses outside the research could reasonably place the subjects at risk of criminal or civil liability or be damaging to the subjects’ financial standing, employability, or reputation.

For the UK, this survey does not fit any of the categories needing approval by a National Health Service Research Ethics Committee (NHR REC) (see http://www.hra.nhs.uk/resources/before-you-apply/is-nhs-rec-review-required/).

Criterion measures

The Patient Health Questionnaire-9 (PHQ-9) is a 9-item measure that assesses the frequency of experiencing symptoms of major depressive episode, as defined in the Diagnostic and Statistical Manual of Mental Disorders Fourth Edition, during the previous 2-week period plus one added item assessing the level of disturbance of these symptoms.¹ The Medical Outcomes Study Cognitive Functioning Scale-Revised-acute form (MOS COG-R) is a 6-item instrument that measures the frequency of problems in a range of day-to-day cognitive functions, such as memory, attention, and reasoning, in the previous 1-week period.^2,3 The Patient Global Impression of Severity scale (PGI-Severity) consists of a single item to assess the severity of the respondent’s depression at the time of assessment.⁴ The 6-item Work Productivity and Activity Impairment Questionnaire: Specific-Health Problem (WPAI:SHP) measures the impact of any specific health problem (in this case, depression) on respondents’ work productivity (including the duration of work time missed due to depression, as well as decreases in productivity when working while experiencing depression) and non-work related activities (eg, childcare) over the past 7 days.⁵ The modified Lam Employment Absence and Productivity Scale (LEAPS) is a 10-item questionnaire to assess occupational functioning and impairment over the previous 2-week period.⁶ The 5-item Sheehan Disability Scale (SDS) measures the degree to which mental disorder symptoms have disrupted a respondent’s work/school, social, and family life in the preceding week.^7,8

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Acknowledgments

The authors thank Jakob Bjorner, MD, PhD, of Optum, Inc., who assisted with some of the data analyses and interpretation (particularly the CFA). Editorial assistance was provided by Julie Adkins of Anthemis Consulting Ltd and funded by Lundbeck SAS. The study and editorial assistance in preparing the paper were funded by Lundbeck SAS. Lundbeck personnel were involved in the study design, in the collection, analysis, and interpretation of data, in the writing of the report, and in the decision to submit the article for publication. Preliminary results were presented at the 16th Annual European Congress of the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) as a poster presentation. November 2–6, 2013 Dublin, Ireland. The poster’s abstract was published in “Poster Abstracts” in Value in Health (Value in Health 2013;16:A330).

Disclosure

RWL has received speaker honoraria from the Canadian Network for Mood and Anxiety Treatments, the Canadian Psychiatric Association, Hansoh, Lundbeck, the Lundbeck Institute, and Pfizer; has received research funding from BC Leading Edge Foundation, Brain Canada, the Canadian Institutes of Health Research, the Canadian Network for Mood and Anxiety Treatments, Janssen, Lundbeck, the Movember Foundation, Pfizer, St. Jude Medical, University Health Network Foundation, and the VGH Foundation; and has served on consulting/advisory boards for Akili, Allergan, the Asia-Pacific Economic Cooperation, the Canadian Depression Research and Intervention Network, the Canadian Network for Mood and Anxiety Treatments, CME Institute, Janssen, Lundbeck, Medscape, Otsuka and Pfizer. FXL, DS, BR, and ND were full-time employees of Lundbeck at the time of the study. AY and MKW are full-time employees of Optum, Inc., which received funding from Lundbeck to design the study and analyze the data; however, no financial payment was provided for their involvement in the development of the manuscript. The authors report no other conflicts of interest in this work.