Depression and anxiety in later life (ancillary study)

Depression and anxiety in later life (ancillary study)

Contact: Almar Kok

Introduction
As from the start of LASA a side study on depression and anxiety was planned. For this, it was necessary to add two types of additional data-collection to the existing LASA data-base.

Psychiatric Diagnostic data
The interviews necessary to gather diagnostic data are time-consuming. A two-stage screening design was adopted through which selected groups of respondents were approached to take part in diagnostic interviews.

Follow-up data
Three-year intervals were deemed too long too capture the natural history of depression. Therefore, additional data were collected in between the three-yearly LASA interview cycles.

The resulting data-base will be described in detail here (section 2). Please note that, given the complexities of two-stage screening designs, it is advisable to contact members of the depression/anxiety research group before embarking on analyses with the data. Furthermore, a side study on Post Traumatic Stress Disorders was included in 1989/9, which will be described in section 3.

Design of the LASA side study on late-life depression
A two-stage screening design implies that all eligible respondents are screened, while only selected groups are approached to be interviewed with the diagnostic interview. This procedure was used throughout the LASA study.

The design and the resulting numbers subjects participating in different stages of the study are summarised in figure 1. At baseline (LASA-B), 3107 elderly subjects participated in the LASA baseline interview. Due to item non-response on the CES-D, 51 subjects were lost, yielding 3056 subjects participating in the baseline measurement for the depression study. All the depressed (CES-D ≥ 16) and a similarly sized random sample of the non-depressed (CES-D < 16) were approached to participate in the diagnostic interviews. The resulting numbers are in figure 1. All those participating in the diagnostic interviews were then approached to take part in a 5-monthly postal questionnaires. These questionnaires contained data on depressive symptoms (CES-D), recent changes in health/chronic physical illness, functional limitations, perceived health, pain, living circumstances and life-events. The postal questionnaires did not contain data on anxiety.

After three years (1995/6), the second cycle of LASA interviews took place (LASA-C). All those who were depressed (CES-D ≥ 16) at baseline (n=448) and all those newly depressed after three years were approached for diagnostic interviews. Due to financial constraints, no diagnostic data on anxiety disorders were gathered in the 1995/6 interview cycle.
During the next 3-year interval, the postal follow-ups continued, but only in the depressed cohort. Approached were all those depressed at baseline, who had taken part in the 1992/3 diagnostic interviews (n=330). At the next LASA interview cycle (1998/9, LASA-D), again all those originally in the depressed cohort and all the newly depressed were approached for diagnostic interviews. This time finance was available to include data on anxiety disorders (CIDI). The postal questionnaire study stopped after that. In the 2001/2 LASA interview cycle (LASA-E) again all those originally in the depressed cohort and all the newly depressed were approached for diagnostic interviews. Again, the diagnostic data-collection involved both depressive and anxiety disorders.

Baseline interview
CES-D; n=3056

Figure 1: Schematic summary of the design (pdf)

This procedure resulted in a maximum of 15 observations of depressive symptoms (CES-D), and four diagnostic assessments (at baseline, after three years, six years and after 9 years), covering 9 years.

For a paper on the natural history of late life depression the data on the first 6 years concerning the depressed cohort were cleaned and analysed (Beekman et al. 2002). Over the first 6 years, a maximum of 14 observations of depressive symptoms (CES-D) was available, and three diagnostic interviews (DIS). The average number of valid CES-D observations was 9.81 (SD 3.92). For this study, inclusion was deemed useful in those with (i) baseline CES-D, (ii) baseline diagnostic interview and (iii) minimally two follow-up measures of depressive symptoms. This reduced the sample to n=277 (61.8% of the original 448 depressed subjects at baseline). Data on the response per observation of the n=277 cohort are summarised in table 1.

Table 1: Response to follow-up of a community based cohort of depressed elderly: 14 observations covering 6 years.

¹ Post a = first wave of postal questionnaire

The data were partly derived from face-to-face interviews and partly from postal questionnaires. As a mode effect was clearly operative: the scores derived from the postal questionnaires were systematically higher than those in the interviews. As postal questionnaires and interviews alternated, it was possible to quantify the mode effect and make an appropriate adjustment, using a generalized T-score transformation.
This has been described in detail in a paper (Geerlings et al. 1999). Both files with raw data and files with adjusted data are available.

The side study on depression has grown into a very rich, but complex dataset. The two-stage screening procedure has proven economical, but increases the complexity of the dataset. Those who want to use the side study data are encouraged to do so, but, to avoid misunderstandings with the complex dataset, please contact one of the members of the anxiety/depression group before starting analyses.

Design of the LASA side study on Post Traumatic Stress Disorders
Post Traumatic Stress Disorders (PTSD) were studied in the interview cycle of 1998/9. A two-phase sampling procedure was used to study the prevalence of PTSD. As screener the Self-Rating Inventory for Posttraumatic Stress Disorder (SRIP; Hovens et al. 1994, van Zelst et al. 2003) was used. To set apart cases with a high chance of meeting diagnostic criteria for PTSD a cut-off was set at 52 based on previous work on the SRIP. At this cut-off the SRIP had a sensitivity of 83% and a specificity of 72%, using the Clinician-Administered PTSD Scale (CAPS) as the gold standard in a mixed outpatient and clinical population. After dichotomizing, there were 47 screen positives and 1674 screen negatives. All screen positives were approached for a psychiatric diagnostic interview using the Comprehensive International Diagnostic Interview (CIDI)-version 2.1 Of these 41 completed the interview. Six participants were lost due to cognitive inability or refusal. In addition, a random sample of 381 screen-negative respondents was also interviewed using the CIDI. (The random sample of 381 was selected from the 650 CIDI interviews included in the LASA- study. As the selection for the CIDI was partially based on CES-D scores, which also correlates with the PTSD screener, we corrected for that by taking only a proportional random sample from CES-D positive CIDI’s.)

Loss of participants and loss of data
Attrition will not be described in detail here. The initial non-response is described in papers on NESTOR (Knipscheer et al. 1995), a basic publication on LASA (Deeeg et al. 1994) and specific papers on the prevalence of depression (Beekman et al 1995) and anxiety (Beekman et al. 1998). Attrition over the first three years is described in a paper on the emergence and persistence of depression (Beekman et al. 2001). Attrition over the first six years is described in a further paper on the prognosis of depression (Beekman et al. 2002). These papers include descriptions of the different types of attrition, the factors associated with attrition and discussion of the effects this may have on the results.

Measurement instruments
(5.1) As a screener for depression, the Center for Epidemiologic Studies Depression Scale was used (Radloff et al. 1977). This is a twenty item self-report scale devel­oped to measure de­pres­sive symptoms in the commu­nity. It has been widely used in older community samples and has good psycho­metric proper­ties in elderly samples (Hi­mmelf­arb 1983, Hertzog 1990, Radloff & Teri 1986). Due to the deliberate emphasis on items tapping the affective dimension of depression, the overlap with sympt­oms of physical illness has been shown to be minimal in a number of studies (Berkman et al. 1986, Foelker & Schewchuk 1992). At the time LASA was designed, a Dutch translation was available, but had not been thoroughly tested. In the pilot study phase of LASA, the CES-D was translated (to- and fro) by native speakers. The resulting translation was tested and compared on several psychometric properties with the existing translation. The Dutch transla­tion had similar (favourable) psychome­tric proper­ties to the original scale. The results of the literature search concerning the CES-D, the psychometric performance of the two translations of the CES-D in elderly in the Netherlands and the resulting scale were published (Beekman et al. 1994). The CES-D genera­tes a total score which can range from 0-60. In order to identify respon­dents with levels of depres­sion which are clinically relevant, we used the generally used cut-off score >16. At this cut-off, the criterion validity of the CES-D for major depress­ion (one-month recency) was excel­lent (se­nsitiv­ity 100%, specificity 88%) (Beekman et al. 1997).

(5.2) To diagnose depression and anxiety, the Diagnostic Interview Schedule (DIS, Robins et al 1981) was used. The DIS was designed for epidemiological research and has been widely used among the elderly. Interviewers were fully trained by certified staff, using the official Dutch translation of the DIS. At the time LASA started, the DSM-III version of the DIS was available in the Netherlands. For economic reasons, the full DIS was not used. The available diagnostic categories are Major Depressive Disorder (MDD), Dysthymic Disorder (DD), Panic Disorder (PAN), Obsessive Compulsive Disorder (OCD), Generalised Anxiety Disorder (GAD and Phobic Disorders (PHOB) (both social- and simple phobias). Those with both MDD and DYSTH can be categorised separately as double depression. Data on recent loss-events are available, allowing the use of exclusion criteria with regard to mourning. The DIS also includes questions on age at onset, number of episodes, recency of the last episodes and allows making diagnoses over several time-frames.
In the course of the study, the classification of anxiety disorders changed somewhat. As a new study on Post Traumatic Stress Disorder (PTSD) was added to the design in 1997, the CIDI was used to diagnose anxiety disorders as of the third LASA cycle (1998/9). This yields DSM-IIIR diagnoses of all the mentioned anxiety disorders. The measurement of depressive disorders remained unchanged.

Specific issues and composite measures
6.1 Diagnostic categories. Using the data different diagnostic categories can be constructed. Algorithms for the conversion of the DIS/CIDI items to DSM-III/DSM-IIIR diagnoses are available with the DIS. As the algorithms are direct translations of the DSM criteria, additional categories can be easily constructed. Examples are ‘minor depression (DSMIV research category), double depression, sub threshold depression, sub threshold anxiety, mixed anxiety/depression. These algorithms are not given here, but the resulting diagnosis are available.

6.2 Parameters of the prognosis of depression The available data can be used to create composite parameters for the prognosis. Examples are symptom severity (the average CES-D score over all observations over time), duration of symptoms (the percentage of observations in which the subjects reported elevated CES-D symptom-levels), and clinical types of course of depression. The course types distinguished were remission, remission with recurrence, a chronic intermittent-, and a chronic course (Geerlings et al 2000). A remission was defined as a combination of (1) a relevant (see below for description) decline of symptoms, (2) the subject remaining non-depressed (CES-D score < 16 and no DSM affective disorder diagnosis) throughout the rest of the study. A remission with recurrence was defined as a remission, in which the subject suffered a relevant increase of symptoms later on in the study. A chronic-intermittent course type was defined as more than one remission, followed by a recurrence of symptoms. A chronic course was defined as 80% or more depressed observations.

For the classification of course types, criteria to define a relevant change had to be defined, which are both statistically sound and clinically relevant. In order to prevent random fluctuation to have undue influence on the results, a statistically relevant change was defined, taking into account the reliability and both the average score and standard deviation of the CES-D in this cohort. The criterion for a reliable change thus calculated was 3,4. To be clinically relevant, a change of 5 points would qualify as a middle to large effect-size in the literature on power analysis. Therefore, a change of 5 CES-D points was chosen as criterion for a relevant change. This had the added advantage that it is similar to what earlier studies using the CES-D have used as criterion for a relevant change. For the purpose of defining course types, a further criterion was that the cut-off of symptoms that is generally regarded to be clinically meaningful was crossed. Therefore, the criterion for a relevant change was that, between measurements, the change was > 5 points, thereby crossing the cut-off of 16. These composite indicators of the prognosis are available.

Additional data
The DIS contains not only data on symptoms of anxiety and depression. Personal histories for each disorder can be reconstructed. Family histories of affective disorders, anxiety dis­orders, substance abuse and conduct disorders were assessed with a questionnaire construc­ted for the LASA study which was built into the diagnostic interview. Treat­ment history was similarly assessed with a separate question­naire, which was built into the diagnostic interview. Moreover, as there was no specific questionnaire for life-events in the baseline LASA interview, a Holmes and Rahe type questionnaire, tapping both recent (past year) and more distant (childhood and war-time experiences) was also added to the diagnostic interview (Beekman et al. 1995). These data are also available on file.

References

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