Methods
Participants
The Netherlands Study of Depression in Older persons (NESDO) is an ongoing multi-site cohort study designed to examine the (determinants of the) course and consequences of depressive disorders in older persons (≥60 years). Detailed description of the design and study sample is given in Comijs et al..[22] In short, NESDO included 378 depressed patients (having MDD, dysthymia or minor depression according to DSM-IV criteria) and 132 non-depressed adults, aged 60 through 93 years. Participants were recruited in five regions in the Netherlands from both mental health care facilities and general practitioners. Participants were excluded when they had a dementia diagnosis or were suspected for dementia based on clinician's judgement. In addition, to be sure that participants were able to fully understand and answer the questions, they were only included when they had a Mini Mental State Examination-score (MMSE)[23] of 18 or higher (out of 30 points), and when they had sufficient command of the Dutch language. The response rate of the depressed persons from the mental health institutions was estimated 48.7%, and from the general practices 60.3%.[22] Non-depressed comparisons were recruited from general practitioners (response rate 66.7%), and were included when they had no lifetime diagnosis of depression, dementia or other serious psychiatric disorders, and good command of the Dutch language.[22] The overall sample of 510 persons had a mean age of 70.6 years (SD: 7.3; range 60–93) and consisted of 331 (64.9%) women and 179 (35.1%) men. The mean level of education was 11.0 years (SD = 3.6; range 5–18 years). The majority of the sample had the Dutch nationality (99.4%). The depressed persons did not differ from the non-depressed comparison group with respect to mean age and sex, but they had a lower level of education, were more often divorced or widowed, and had a lower score on the MMSE.[22]
Materials and Procedure
Data Collection. Data collection of the baseline NESDO measurement started in 2007 and was finished in September 2010. It included an extensive assessment of psychopathology, socio-demographic characteristics, physical health and physical health markers, cognitive functioning, psycho-social functioning, and life style variables. The course of late-life depression was followed up every 6 months by means of a postal assessment, including questionnaires on the severity of depressive symptoms and physical health in the past 6 months, incident (chronic) stressors and functional limitations, and use of medications and health care. The questionnaires were the same questionnaires that were used during the face-to-face assessments.[22] A second face-to-face assessment was performed 2 years after the baseline assessment. It started in 2009 and was completed in September 2012. It consisted of all baseline measures (determinants and outcome variables) that were open to change, such as severity of psychopathology and diagnostics. Well-trained research assistants, mainly consisting of psychologists and mental health care nurses, conducted the interviews. All interviews were audio taped and were regularly controlled for their quality.
Ethical Issues. The study protocol of NESDO has been approved centrally by the Ethical Review Board of the VU University Medical Center, and subsequently by the local ethical review boards of the Leiden University Medical Center, University Medical Center Groningen and the Radboud University Medical Center in Nijmegen. Written informed consent was obtained from all participants at the start of the baseline assessment. Written informed consent was asked for participating in the study, for permission to use genetic information, to retrieve medical information from the GP's, and to link information to external databases. A privacy protocol has been developed in which confidentiality of data is guaranteed by using a unique research ID number for each respondent, which enables to identify individuals without using their names. Only the data manager has access to the record that links the ID number with the name of the participant.[22] All data are available on request (see https://nesdo.amstad.nl/).
Course of Depression. Diagnoses of major depression, dysthymia and minor depression according to DSM-IV-TR criteria[24] at baseline and at two-year follow-up were assessed with the Composite International Diagnostic Interview (CIDI; WHO version 2.1). The CIDI is a structured clinical interview that is designed for use in research settings and has high validity for depressive and anxiety disorders.[25,26] Questions were added to determine the DSM-IV research diagnosis of current minor depression.[22]
More detailed information about the severity of the depressive symptoms was obtained from the postal questionnaires, that were send to the respondents every 6 months. Severity of the depressive symptoms was assessed with the Inventory of Depressive Symptoms (IDS).[27] The IDS is a 30-item self-report scale that was developed to carefully assess all core criterion diagnostic depressive symptoms. The scale has acceptable psychometric properties in depressed outpatients e.g.[27,28] and depressed inpatients.[29] The IDS is sensitive to both change over time and to differences between treatment conditions.[30] Chronbach's alpha for the IDS in our sample was 0.83. The IDS was also included in the baseline and 2-year follow-up assessment, resulting in a total of 5 IDS ratings per participant. The IDS-scores range between 0 and 84, and is categorized according to severity as; < 14: no depression, 14–25: mild depression, 26 – 38 moderate depression, 39–48: severe depression and ≥ 49: very severe depression. Course types of depressive symptoms were computed from patients from whom we had at least 4 out of 5 IDS scores. We distinguished 5 course types:
remission, defined as at least the last two observations IDS score < 14,
intermittent depression, defined as at least one of the observations IDS < 14 (not being the last two observations),
chronic depression, defined as all IDS scores > 14 and 38 and sub classified as:
chronic mild to moderate depression, defined as all IDS scores between 14 and 26,
chronic moderate to severe depression, defined as all IDS scores between 26 and 84,
chronic depression with variable severity, defined as IDS scores varying between 14 to 84.
Determinants of Depressive Disorder at 2-year Follow-up. Socio-demographic characteristics including age, sex, years of education, and partner status were assessed with standard questions. Sampling characteristics included sampling site (Amsterdam, Leiden, Groningen, Apeldoorn/Zutphen and Nijmegen) and sampling frame (primary care, ambulant health care and clinical health care).
Clinical variables included; first episode MDD (y/n), comorbid dysthymia (y/n), age of onset, comorbid anxiety disorder(s) (y/n), severity of depressive symptoms, cognitive functioning and number of chronic diseases. Information about the first episode MDD, recurrent MMD, dysthymia, and age of onset were all obtained from the CIDI (WHO version 2.1). Comorbid anxiety disorders (General Anxiety Disorder, Panic Disorder, Agoraphobia and Social Phobia) were also assessed using the CIDI. The Mini-Mental State Examination (MMSE)[23] was used to assess global cognitive functioning. The presence of chronic diseases was assessed by means of a self-report questionnaire. The participants were asked whether they currently or previously had any of the following chronic diseases or disease events: cardiac disease (including myocardial infarction), peripheral atherosclerosis, stroke, diabetes mellitus, COPD (asthma, chronic bronchitis or pulmonary emphysema), arthritis (rheumatoid arthritis or osteoarthritis), cancer, or any other chronic disease. The accuracy of self-reports of these diseases was compared to general practitioner information, and was shown to be adequate and independent of cognitive impairment.[31] Use of anti-depressive medication and benzodiazepines was determined by inspection of the medication that the participants brought in.
Statistical Analyses
Descriptive statistics were used to describe attrition and its determinants according to depression status at baseline. Next, diagnoses at 2-years follow-up were described according to baseline diagnostic status. In addition, specific course types were described according to the severity of depressive symptoms obtained from the five 6-monthly assessments with the IDS (see description IDS).
The socio-demographics, clinical and treatment characteristics were described for the depressed patients according to their depression diagnoses (MDD, dysthymia or minor depression) according to DSM-IV-R criteria at 2-year follow-up. Associations between baseline characteristics and the outcome measure depression diagnoses (y/n) at 2-year follow-up, were first assessed with univariate logistic regression analyses. Subsequently, when p < 0.10 the variables were entered in a final multivariate model. All analyses were performed by using SPSS 21.0 (IBM SPSS, Chicago, IL).
BMC Psychiatry. 2015;15(20) © 2015 BioMed Central, Ltd.
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