Journal of Anxiety Disorders 32 (2015) 73–80
Contents lists available at ScienceDirect
Journal of Anxiety Disorders
Subthreshold and threshold DSM-IV generalized anxiety disorder in Singapore: Results from a nationally representative sample Siau Pheng Lee ∗ , Vathsala Sagayadevan, Janhavi Ajit Vaingankar, Siow Ann Chong, Mythily Subramaniam Research Division, Institute of Mental Health, Singapore
a r t i c l e
i n f o
Article history: Received 8 October 2014 Received in revised form 16 March 2015 Accepted 18 March 2015 Available online 28 March 2015 Keywords: Population-based survey Epidemiology Prevalence Disability Comorbidity Singapore
a b s t r a c t Previous nationally representative studies have reported prevalence of DSM-IV generalized anxiety disorder (GAD). However, subthreshold and threshold GAD expressions remain poorly understood. The current study examined the prevalence, correlates and co-morbidity of a broader diagnosis of GAD in Singapore. The Singapore Mental Health Study (SMHS) was an epidemiological survey conducted in the population (N = 6616) aged 18 years and older. The Composite International Diagnostic Interview version 3.0 (CIDI 3.0) was used to establish mental disorder diagnoses. The lifetime prevalence for subthreshold GAD (2.1%) and threshold GAD (1.5%) in the current sample was found to be lower than in Western populations. Younger age group, Indian ethnicity, previously married, chronic physical conditions, and being unemployed were associated with higher odds of having more severe expression of generalized anxiety. The relatively lower prevalence rate of subthreshold GAD expression suggests possible cultural interferences in the reporting and manifestation of anxiety symptomatology. Despite the low prevalence, significant impacts on functioning and comorbidity among subthreshold generalized anxiety cases indicate the importance of early treatment to ensure a better prognosis. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Generalized anxiety disorder (GAD) is characterized by excessive, persistent worry and anxiety lasting for a duration of at least 6 months, accompanied by symptoms, such as restlessness, fatigue, poor concentration, irritability, muscle tension, and sleep disturbances causing substantial distress and impairment in daily activities (APA, 1994, 2013). In addition, the waxing and waning symptomology that changes from subthreshold syndromes to full symptomatic GAD is common among GAD sufferers (Angst, Gamma, Baldwin, Ajdacic-Gross, & Rössler, 2009; Ballenger et al., 2001). Diagnosing GAD poses significant challenges given the relatively broad range of prevalence estimates reported across countries. Even among community studies which utilized similar diagnostic criteria, instruments, and sampling methods, the prevalence varies considerably. For instance, the lifetime prevalence was 0.8% in metropolitan China and 2.3% in Korea, as opposed to 5.7% in United
∗ Corresponding author at: Research Division, Institute of Mental Health, 10 Buangkok View, Singapore 539747, Singapore. Tel.: +65 6389 3623; fax: +65 6389 2795. E-mail address: siau pheng [email protected] (S.P. Lee). http://dx.doi.org/10.1016/j.janxdis.2015.03.008 0887-6185/© 2015 Elsevier Ltd. All rights reserved.
States and 6.0% in New Zealand (Cho et al., 2007; Kessler, Berglund, et al., 2005; Lee, Tsang, Zhang, et al., 2007; Oakley Browne, Wells, Scott, & Mcgee, 2006). The observed differences in prevalence estimates across different cultures raise issues with regard to cross-cultural variability in psychiatric epidemiology. The lack of measurement equivalence of the instrument, incapability of the diagnostic criteria to identify pathology across cultures, or a true difference of prevalence rate among different cultural groups have been suggested as possible mechanisms underlying the observed differences (Asnaani, Richey, Dimaite, Hinton, & Hofmann, 2010; Lewis-Fernández et al., 2011). In addition, constant revisions of the diagnostic criteria across the various versions of Diagnostic and Statistical Manual of Mental Disorders (DSM) reflect uncertainty in the definition and diagnosis of GAD, and further increase the complexity of the matter (Lee et al., 2009). Increase in the duration of “worrying” from 1 month to 6 months in DSM-III-R, was made in an effort to differentiate a transient anxiety response to stress from GAD. The subsequent version of the manual, DSM-IV, again redefined GAD, additionally stipulating that a) the anxiety and worry must be excessive, b) the worry must be difficult to control, and c) autonomic symptoms were replaced by at least three of the six key hypervigilance/tension associated symptoms from the diagnostic criteria (Beesdo-Baum et al., 2011; Carter, Wittchen, Pfister, & Kessler, 2001).
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S.P. Lee et al. / Journal of Anxiety Disorders 32 (2015) 73–80
Such changes in the DSM-IV GAD diagnostic criteria have made it more difficult for individuals to be diagnosed with GAD. Yet, even those with subthreshold level of generalized anxiety expressions may also suffer from significant impairment, pathological anxiety, and comorbid conditions (Carter et al., 2001; Haller, Cramer, Lauche, Gass, & Dobos, 2014). For instance, increasing the required duration of worry precludes individuals experiencing symptoms for less than 6 months from receiving a diagnosis. However, evidence suggests that this group of cases also show significant daily impairment (Kessler, Brandenburg, et al., 2005), similar to levels experienced by individuals who have met the 6-month duration criterion (Lee et al., 2009). Thus, these diagnostic changes impact individuals with subthreshold symptoms as they may not receive the clinical attention they need. Furthermore, the relatively high prevalence of subthreshold GAD across epidemiological samples, ranging from 3.6% to 13.7%, underscores the importance of enhancing our understanding of the implications of such changes (Carter et al., 2001; Haller et al., 2014). Despite their disabling characteristics, and significant disease burden, the nature of milder forms of generalized anxiety expressions remains poorly understood, particularly in an Asian context (Lee et al., 2009). Given the urgency to understand the disorder epidemiology, this paper aimed to assess the prevalence of various levels of generalized anxiety expressions, as well as their relationship to comorbid conditions, socio-demographic factors, and impairment, using the data from the Singapore Mental Health Study (SMHS). 2. Method 2.1. Sample The SMHS was a nationwide epidemiological survey conducted in Singapore from December 2009 to December 2010. A total of 6616 respondents, aged 18 years and older were recruited in the survey. Disproportionate stratified sampling was used to obtain an equivalent proportion of 30% of the three main ethnic groups in Singapore (Chinese, Malay, and Indian) in the current sample. Respondents were randomly selected from a national database, and were approached at their households for face-to-face interviews. A response rate of 75.9% was achieved in the study. No significant differences were found in age and gender between respondents and non-responders. However, Chinese and those belonging to other ethnic groups were more likely to be non-responders than Malays and Indians. Detailed methodology of the current survey has been described in a prior article (Subramaniam et al., 2012). The weighted mean age of respondents was 43.9 years (S.E. = 0.3). Weighted distribution by ethnic group was 76.9% Chinese, 12.3% Malay, 8.3% Indian, and 2.4% Other ethnicities, which is representative of the Singapore population based on the 2007 population census. Fifty-two percent of respondents were female, and 48.5% were male. The majority of respondents were married at the time of the survey (62.4%), 28.9% of respondents were single, 4.2% were divorced/separated, and 4.4% of respondents were widowed. In addition, the majority of respondents had completed at least secondary level education (secondary, 27.6%; Pre-U/junior college/diploma, 22.4%; vocational, 7.9%; university, 22.4%), 14.7% of respondents had primary level education, and 5.5% had preprimary level education.
the WHO-CIDI Training and Research Center. Study team members who attended the training program conducted an intensive 3-week training program for lay interviewers. CIDI v3.0 was adapted to the Singaporean context. Other than the English version, the study also used the Malay and Chinese versions of the instrument. The Malay language (Bahasa Melayu) version of CIDI was fully translated by the study team, whereas the Chinese language version was adapted from a version translated by the WMH-CIDI group in China. We did not develop a Tamil version, the major language spoken by Indians in Singapore, as we made the assumption that most Indians are conversant in English (Department of Statistics, Ministry of Trade and Industry, Singapore, 2013). Respondents chose the language (i.e. English, Chinese, Malay) in which they were most comfortable to complete the survey. Three screening questions prefaced the GAD module: (1) “Did you ever have a time in your life when you were a “worrier” – that is, when you worried a lot more about things than other people with the same problems as you?,” (2) “Did you ever have a time in your life when you were much more nervous or anxious than most other people with the same problems as you?,” and (3)“Did you ever have a period lasting one month or longer when you were anxious and worried most days?” Respondents who answered “yes” for at least one of the screening questions proceeded to the GAD module. If respondents answered “no” to all three screening questions, the GAD module was skipped. Diagnoses of mental illnesses reported in this paper were applied without using DSM-IV hierarchy exclusion rules, unless stated otherwise. Chronic physical conditions were assessed using a modified version of the CIDI chronic physical condition checklist. All respondents completed the 30-day functioning module in the CIDI and the EQ-5D questionnaire. The EQ-5D questionnaire measures various aspects of health-related quality of life, including mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. 2.3. Assessment of DSM-IV generalized anxiety disorder and subthreshold expressions The GAD module in the CIDI starts with a checklist of types of worries. Assessment of DSM-IV GAD is described in Table 1. A skipping pattern was applied depending on respondents’ responses to the items. Levels of generalized anxiety expressions included (a) worrying for at least 1 but less than 3 months, (b) worrying for at least 3 but less than 6 months, (c) subthreshold GAD, and (d) threshold GAD. Respondents who reported worrying for at least 3 months and had at least 2 of the other DSM-IV GAD criteria (B, C, or E), were classified as “subthreshold GAD,” whereas respondents who reported at least 6 months of worrying and met criteria B, C, and E were considered “threshold GAD” cases. These criteria were first used in Carter et al.’s (2001) study, and are used here to facilitate cross-cultural comparisons. A DSM-IV GAD diagnosis also contains two exclusion criteria. Criterion D stipulates that the focus of the worry and anxiety should not be confined to features of another Axis I disorder, whereas criterion F states that the anxiety must not be due to the direct physiological effects of substance use, medical conditions, or other mood disorders. Respondents only received a DSM-IV GAD diagnosis if they met the abovementioned criteria.
2.2. Instruments
2.4. Statistical analysis
The SMHS used the Composite International Diagnostic Interview version 3.0 (CIDI v3.0) as the main survey instrument. The use of CIDI requires completion of a training program offered by
Statistical analysis was performed using the Statistical Analysis Software (SAS) System version 9.3 (SAS Institute, Cary, NC) and Stata statistical software version 13.0 (StataCorp, College
S.P. Lee et al. / Journal of Anxiety Disorders 32 (2015) 73–80
75
Table 1 Assessment of DSM-IV Generalized Anxiety Disorder in Composite International Diagnostic Interview (CIDI) version 3.0. Criteriona
Fulfilled if. . .
The subsequent items of GAD module were skipped if. . ..b
Criterion A part 1 Excessive anxiety and worry Criterion A part 3 Anxiety about a number of events or activities Criterion D Worry and anxiety is not confined to another Axis 1 disorder
‘Yes’ to either one of 3 screening questions in the screening module Endorsed worry for more than one type of event/activity (e.g. finances, physical appearance and etc.) Endorsed worry to items not related to mental health, substance use, phobic and obsessive compulsive situations, separation anxiety issue
‘No’ to all three screening questions
Criterion B Difficult to control the worry
‘Often’ or ‘Sometimes’ in how often they had difficulty in controlling their worry
Criterion A part 2 Anxiety occurring more days than not for at least 6 months
Reported ‘Six months or longer’ as the longest period when they were anxious on most days
‘Less than one month’ reported
Criterion C Associated key symptoms
Endorsed at least three or more of the six key symptoms (i.e. restlessness, easily fatigued, difficulty concentrating, irritability, muscle tension, sleep disturbance)
Endorsed less than two key symptoms (i.e. 0 or 1 symptom)
Criterion E part 1 Cause distress
Endorsed emotional distress they experienced, or endorsed they could not think about anything because of the worry
Criterion E part 2 Cause impairment in functioning
Endorsed worry interfered with work, social life, personal relationship, or ability to carry daily activities, or as reflected in Sheehan Disability Scale.
Criterion F part 1 Worry and anxiety is not due to physiological effects of a substance or other medical conditions
Did not endorse worry to be due to physical causes (e.g. physical illness, injury), or use of medication, drugs, or alcohol
Criterion F part 2 Worry and anxiety is not due to other mood disorders
No comorbidity of mood disorders as reflected in diagnosis in respective disorder specific CIDI module, or with any comorbid of mood disorders while GAD age of onset is younger, age of recency is older (i.e. more recent), duration of persistence is longer than other mood disorders
a b
Endorsed only one specific type of worry
Did not endorse distress and impairment that caused by their worry or anxiety
Criteria fulfillment is presented in accordance with sequence of items in the CIDI GAD specific module. Unless as stated in the table, the subsequent items were asked without skipping.
Station, TX). The data was weighted to adjust for oversampling, and post-stratified by age and ethnicity distribution between the survey sample and Singapore population. Worrying for less than one month, worrying for at least 1 month, worrying for at least 3 months, subthreshold GAD, and threshold GAD were organized into a single 5-level ordinal variable with subsequent points on the scale indicating increasing severity level of generalized anxiety expression (i.e. threshold GAD is more severe than subthreshold GAD and etc.). Ordinal logistic regression was performed to examine the association between the various levels of generalized anxiety expressions and socio-demographic factors (including age group, ethnicity, gender, marital status, education level, presence of chronic physical conditions, employment status, and income level). After adjusting for age group, gender, and ethnicity, multivariate logistic regression was used to calculate the odds ratios for comorbidity and impairment. Poisson regression was used to calculate the rate ratios of functioning days lost using data from the 30-day functioning module. 3. Results 3.1. Prevalence of worrying and GAD Prevalence estimates for the different levels of generalized anxiety expressions are presented in Table 2. Among the respondents, 5.7% reported worrying for at least one month (inclusive of more severe levels), 3.7% reported worrying for at least 3 months
(inclusive of subthreshold GAD and threshold GAD), 2.1% had subthreshold GAD (inclusive of threshold GAD), and 1.5% had threshold GAD. After applying DSM-IV hierarchy exclusion rules, 0.9% of respondents received a DSM-IV GAD diagnosis. Table 2 shows the association between generalized anxiety expressions and socio-demographic variables. Being younger, Indian, of “Other” ethnicities, divorced/separated, widowed, and unemployed significantly predicted more severe levels of generalized anxiety expressions. Those with primary education were less likely to have more severe generalized anxiety expressions than those with university education.
3.2. Comorbidity and impairment of worrying and GAD Table 3 shows the prevalence and odds ratios for comorbidity of lifetime mental illnesses and chronic physical conditions. The majority of respondents who worried for at least one month or had more severe levels of expressions (79.3%) had at least one of the disorders listed in Table 3. Prevalence of comorbid chronic physical conditions was higher than that of comorbid mental illnesses across all generalized anxiety expressions, except the threshold GAD category (any physical conditions, 49.4%; any mental illnesses, 78.8%). Major depressive disorder (MDD) was found to be the most common comorbid mental illness, and chronic pain was the most common physical condition across the generalized anxiety expressions.
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S.P. Lee et al. / Journal of Anxiety Disorders 32 (2015) 73–80
Table 2 Socio-demographic association with levels of generalized anxiety expressions. Worrying ≥1 montha 5.7% (1.9%)
Worrying ≥ 3 months 3.7% (1.6%)
Subthreshold GAD 2.1% (0.6%)
Threshold GAD 1.5% (1.5%)
Odds ratiosb
n
n
OR
95% CI
p-Value
Age group 18–34 82 35–49 39 50–64 24 65 + + 3 Ethnicity 37 Chinese 43 Malay Indian 58 Other 10 Gender 87 Male 61 Female Marital status 59 Single 78 Married 8 Divorced/separated Widowed 3 Education level 39 University Pre-U/Junior College/Diploma 33 22 Vocational 39 Secondary 13 Primary Pre-Primary 2 Any chronic physical condition 83 No Yes 65 Employment status 113 Employed 20 Economically inactive 10 Unemployed Below $19,999 $20,000–$49,999 Above $50,000 a b * **
71 48 22
%
95% CI
n
%
95% CI
%
95% CI
n
%
95% CI
3.17 1.47 1.28 1.26
2.2 0.8 0.5 0.0
4.1 2.1 2.1 2.9
43 37 13 6
2.27 1.68 0.65 1.42
1.4 0.9 0.1 0.0
3.1 27 2.4 19 1.2 10 3.1 0
0.79 0.87 0.34 –
0.3 0.3 0.0 –
1.2 1.4 0.7 –
53 48 21 0
1.76 1.95 1.22 –
1.1 1.2 0.4 –
2.4 2.8 2.0 –
1 0.7 0.4 0.3
0.5 0.2 0.1
1.2 0.8 0.9
0.2 0.007* 0.03*
1.79 1.80 2.93 4.18
1.2 1.3 2.2 1.6
2.4 2.3 3.7 6.8
33 28 27 11
1.61 1.18 1.37 4.32
1.1 0.7 0.8 1.7
2.2 11 1.6 17 1.9 23 6.9 5
0.52 0.70 1.17 1.60
0.2 0.4 0.7 0.1
0.8 1.0 1.6 3.1
29 35 53 5
1.37 1.45 2.63 2.09
0.9 1.0 1.9 0.2
1.9 1.9 3.3 4.0
1.0 1.0 1.5 1.8
0.7 1.1 1.1
1.4 2.0 3.1
1.0 0.004* 0.03*
2.38 1.53
1.7 1.0
3.1 2.1
58 41
1.85 1.37
1.2 0.8
2.5 23 2.0 33
0.43 0.81
0.2 0.4
0.7 1.2
48 74
1.22 1.78
0.7 1.2
1.7 2.4
1.0 1.0
0.7
1.4
0.9
3.08 1.45 1.65 1.66
2.0 1.0 0.0 0.0
4.1 2.0 3.5 4.6
28 57 10 4
1.47 1.27 4.94 4.03
0.7 0.8 1.3 0.0
2.2 21 1.7 32 8.6 2 8.4 1
0.89 0.51 1.00 0.12
0.3 0.2 0.0 0.0
1.4 0.8 2.8 0.4
37 66 17 2
1.48 1.21 7.42 0.18
0.8 0.8 2.9 0.0
2.2 1.7 11.9 0.4
1.0 0.9 4.5 3.3
0.6 2.4 1.2
1.5 0.8 8.4
Contents lists available at ScienceDirect
Journal of Anxiety Disorders
Subthreshold and threshold DSM-IV generalized anxiety disorder in Singapore: Results from a nationally representative sample Siau Pheng Lee ∗ , Vathsala Sagayadevan, Janhavi Ajit Vaingankar, Siow Ann Chong, Mythily Subramaniam Research Division, Institute of Mental Health, Singapore
a r t i c l e
i n f o
Article history: Received 8 October 2014 Received in revised form 16 March 2015 Accepted 18 March 2015 Available online 28 March 2015 Keywords: Population-based survey Epidemiology Prevalence Disability Comorbidity Singapore
a b s t r a c t Previous nationally representative studies have reported prevalence of DSM-IV generalized anxiety disorder (GAD). However, subthreshold and threshold GAD expressions remain poorly understood. The current study examined the prevalence, correlates and co-morbidity of a broader diagnosis of GAD in Singapore. The Singapore Mental Health Study (SMHS) was an epidemiological survey conducted in the population (N = 6616) aged 18 years and older. The Composite International Diagnostic Interview version 3.0 (CIDI 3.0) was used to establish mental disorder diagnoses. The lifetime prevalence for subthreshold GAD (2.1%) and threshold GAD (1.5%) in the current sample was found to be lower than in Western populations. Younger age group, Indian ethnicity, previously married, chronic physical conditions, and being unemployed were associated with higher odds of having more severe expression of generalized anxiety. The relatively lower prevalence rate of subthreshold GAD expression suggests possible cultural interferences in the reporting and manifestation of anxiety symptomatology. Despite the low prevalence, significant impacts on functioning and comorbidity among subthreshold generalized anxiety cases indicate the importance of early treatment to ensure a better prognosis. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Generalized anxiety disorder (GAD) is characterized by excessive, persistent worry and anxiety lasting for a duration of at least 6 months, accompanied by symptoms, such as restlessness, fatigue, poor concentration, irritability, muscle tension, and sleep disturbances causing substantial distress and impairment in daily activities (APA, 1994, 2013). In addition, the waxing and waning symptomology that changes from subthreshold syndromes to full symptomatic GAD is common among GAD sufferers (Angst, Gamma, Baldwin, Ajdacic-Gross, & Rössler, 2009; Ballenger et al., 2001). Diagnosing GAD poses significant challenges given the relatively broad range of prevalence estimates reported across countries. Even among community studies which utilized similar diagnostic criteria, instruments, and sampling methods, the prevalence varies considerably. For instance, the lifetime prevalence was 0.8% in metropolitan China and 2.3% in Korea, as opposed to 5.7% in United
∗ Corresponding author at: Research Division, Institute of Mental Health, 10 Buangkok View, Singapore 539747, Singapore. Tel.: +65 6389 3623; fax: +65 6389 2795. E-mail address: siau pheng [email protected] (S.P. Lee). http://dx.doi.org/10.1016/j.janxdis.2015.03.008 0887-6185/© 2015 Elsevier Ltd. All rights reserved.
States and 6.0% in New Zealand (Cho et al., 2007; Kessler, Berglund, et al., 2005; Lee, Tsang, Zhang, et al., 2007; Oakley Browne, Wells, Scott, & Mcgee, 2006). The observed differences in prevalence estimates across different cultures raise issues with regard to cross-cultural variability in psychiatric epidemiology. The lack of measurement equivalence of the instrument, incapability of the diagnostic criteria to identify pathology across cultures, or a true difference of prevalence rate among different cultural groups have been suggested as possible mechanisms underlying the observed differences (Asnaani, Richey, Dimaite, Hinton, & Hofmann, 2010; Lewis-Fernández et al., 2011). In addition, constant revisions of the diagnostic criteria across the various versions of Diagnostic and Statistical Manual of Mental Disorders (DSM) reflect uncertainty in the definition and diagnosis of GAD, and further increase the complexity of the matter (Lee et al., 2009). Increase in the duration of “worrying” from 1 month to 6 months in DSM-III-R, was made in an effort to differentiate a transient anxiety response to stress from GAD. The subsequent version of the manual, DSM-IV, again redefined GAD, additionally stipulating that a) the anxiety and worry must be excessive, b) the worry must be difficult to control, and c) autonomic symptoms were replaced by at least three of the six key hypervigilance/tension associated symptoms from the diagnostic criteria (Beesdo-Baum et al., 2011; Carter, Wittchen, Pfister, & Kessler, 2001).
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S.P. Lee et al. / Journal of Anxiety Disorders 32 (2015) 73–80
Such changes in the DSM-IV GAD diagnostic criteria have made it more difficult for individuals to be diagnosed with GAD. Yet, even those with subthreshold level of generalized anxiety expressions may also suffer from significant impairment, pathological anxiety, and comorbid conditions (Carter et al., 2001; Haller, Cramer, Lauche, Gass, & Dobos, 2014). For instance, increasing the required duration of worry precludes individuals experiencing symptoms for less than 6 months from receiving a diagnosis. However, evidence suggests that this group of cases also show significant daily impairment (Kessler, Brandenburg, et al., 2005), similar to levels experienced by individuals who have met the 6-month duration criterion (Lee et al., 2009). Thus, these diagnostic changes impact individuals with subthreshold symptoms as they may not receive the clinical attention they need. Furthermore, the relatively high prevalence of subthreshold GAD across epidemiological samples, ranging from 3.6% to 13.7%, underscores the importance of enhancing our understanding of the implications of such changes (Carter et al., 2001; Haller et al., 2014). Despite their disabling characteristics, and significant disease burden, the nature of milder forms of generalized anxiety expressions remains poorly understood, particularly in an Asian context (Lee et al., 2009). Given the urgency to understand the disorder epidemiology, this paper aimed to assess the prevalence of various levels of generalized anxiety expressions, as well as their relationship to comorbid conditions, socio-demographic factors, and impairment, using the data from the Singapore Mental Health Study (SMHS). 2. Method 2.1. Sample The SMHS was a nationwide epidemiological survey conducted in Singapore from December 2009 to December 2010. A total of 6616 respondents, aged 18 years and older were recruited in the survey. Disproportionate stratified sampling was used to obtain an equivalent proportion of 30% of the three main ethnic groups in Singapore (Chinese, Malay, and Indian) in the current sample. Respondents were randomly selected from a national database, and were approached at their households for face-to-face interviews. A response rate of 75.9% was achieved in the study. No significant differences were found in age and gender between respondents and non-responders. However, Chinese and those belonging to other ethnic groups were more likely to be non-responders than Malays and Indians. Detailed methodology of the current survey has been described in a prior article (Subramaniam et al., 2012). The weighted mean age of respondents was 43.9 years (S.E. = 0.3). Weighted distribution by ethnic group was 76.9% Chinese, 12.3% Malay, 8.3% Indian, and 2.4% Other ethnicities, which is representative of the Singapore population based on the 2007 population census. Fifty-two percent of respondents were female, and 48.5% were male. The majority of respondents were married at the time of the survey (62.4%), 28.9% of respondents were single, 4.2% were divorced/separated, and 4.4% of respondents were widowed. In addition, the majority of respondents had completed at least secondary level education (secondary, 27.6%; Pre-U/junior college/diploma, 22.4%; vocational, 7.9%; university, 22.4%), 14.7% of respondents had primary level education, and 5.5% had preprimary level education.
the WHO-CIDI Training and Research Center. Study team members who attended the training program conducted an intensive 3-week training program for lay interviewers. CIDI v3.0 was adapted to the Singaporean context. Other than the English version, the study also used the Malay and Chinese versions of the instrument. The Malay language (Bahasa Melayu) version of CIDI was fully translated by the study team, whereas the Chinese language version was adapted from a version translated by the WMH-CIDI group in China. We did not develop a Tamil version, the major language spoken by Indians in Singapore, as we made the assumption that most Indians are conversant in English (Department of Statistics, Ministry of Trade and Industry, Singapore, 2013). Respondents chose the language (i.e. English, Chinese, Malay) in which they were most comfortable to complete the survey. Three screening questions prefaced the GAD module: (1) “Did you ever have a time in your life when you were a “worrier” – that is, when you worried a lot more about things than other people with the same problems as you?,” (2) “Did you ever have a time in your life when you were much more nervous or anxious than most other people with the same problems as you?,” and (3)“Did you ever have a period lasting one month or longer when you were anxious and worried most days?” Respondents who answered “yes” for at least one of the screening questions proceeded to the GAD module. If respondents answered “no” to all three screening questions, the GAD module was skipped. Diagnoses of mental illnesses reported in this paper were applied without using DSM-IV hierarchy exclusion rules, unless stated otherwise. Chronic physical conditions were assessed using a modified version of the CIDI chronic physical condition checklist. All respondents completed the 30-day functioning module in the CIDI and the EQ-5D questionnaire. The EQ-5D questionnaire measures various aspects of health-related quality of life, including mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. 2.3. Assessment of DSM-IV generalized anxiety disorder and subthreshold expressions The GAD module in the CIDI starts with a checklist of types of worries. Assessment of DSM-IV GAD is described in Table 1. A skipping pattern was applied depending on respondents’ responses to the items. Levels of generalized anxiety expressions included (a) worrying for at least 1 but less than 3 months, (b) worrying for at least 3 but less than 6 months, (c) subthreshold GAD, and (d) threshold GAD. Respondents who reported worrying for at least 3 months and had at least 2 of the other DSM-IV GAD criteria (B, C, or E), were classified as “subthreshold GAD,” whereas respondents who reported at least 6 months of worrying and met criteria B, C, and E were considered “threshold GAD” cases. These criteria were first used in Carter et al.’s (2001) study, and are used here to facilitate cross-cultural comparisons. A DSM-IV GAD diagnosis also contains two exclusion criteria. Criterion D stipulates that the focus of the worry and anxiety should not be confined to features of another Axis I disorder, whereas criterion F states that the anxiety must not be due to the direct physiological effects of substance use, medical conditions, or other mood disorders. Respondents only received a DSM-IV GAD diagnosis if they met the abovementioned criteria.
2.2. Instruments
2.4. Statistical analysis
The SMHS used the Composite International Diagnostic Interview version 3.0 (CIDI v3.0) as the main survey instrument. The use of CIDI requires completion of a training program offered by
Statistical analysis was performed using the Statistical Analysis Software (SAS) System version 9.3 (SAS Institute, Cary, NC) and Stata statistical software version 13.0 (StataCorp, College
S.P. Lee et al. / Journal of Anxiety Disorders 32 (2015) 73–80
75
Table 1 Assessment of DSM-IV Generalized Anxiety Disorder in Composite International Diagnostic Interview (CIDI) version 3.0. Criteriona
Fulfilled if. . .
The subsequent items of GAD module were skipped if. . ..b
Criterion A part 1 Excessive anxiety and worry Criterion A part 3 Anxiety about a number of events or activities Criterion D Worry and anxiety is not confined to another Axis 1 disorder
‘Yes’ to either one of 3 screening questions in the screening module Endorsed worry for more than one type of event/activity (e.g. finances, physical appearance and etc.) Endorsed worry to items not related to mental health, substance use, phobic and obsessive compulsive situations, separation anxiety issue
‘No’ to all three screening questions
Criterion B Difficult to control the worry
‘Often’ or ‘Sometimes’ in how often they had difficulty in controlling their worry
Criterion A part 2 Anxiety occurring more days than not for at least 6 months
Reported ‘Six months or longer’ as the longest period when they were anxious on most days
‘Less than one month’ reported
Criterion C Associated key symptoms
Endorsed at least three or more of the six key symptoms (i.e. restlessness, easily fatigued, difficulty concentrating, irritability, muscle tension, sleep disturbance)
Endorsed less than two key symptoms (i.e. 0 or 1 symptom)
Criterion E part 1 Cause distress
Endorsed emotional distress they experienced, or endorsed they could not think about anything because of the worry
Criterion E part 2 Cause impairment in functioning
Endorsed worry interfered with work, social life, personal relationship, or ability to carry daily activities, or as reflected in Sheehan Disability Scale.
Criterion F part 1 Worry and anxiety is not due to physiological effects of a substance or other medical conditions
Did not endorse worry to be due to physical causes (e.g. physical illness, injury), or use of medication, drugs, or alcohol
Criterion F part 2 Worry and anxiety is not due to other mood disorders
No comorbidity of mood disorders as reflected in diagnosis in respective disorder specific CIDI module, or with any comorbid of mood disorders while GAD age of onset is younger, age of recency is older (i.e. more recent), duration of persistence is longer than other mood disorders
a b
Endorsed only one specific type of worry
Did not endorse distress and impairment that caused by their worry or anxiety
Criteria fulfillment is presented in accordance with sequence of items in the CIDI GAD specific module. Unless as stated in the table, the subsequent items were asked without skipping.
Station, TX). The data was weighted to adjust for oversampling, and post-stratified by age and ethnicity distribution between the survey sample and Singapore population. Worrying for less than one month, worrying for at least 1 month, worrying for at least 3 months, subthreshold GAD, and threshold GAD were organized into a single 5-level ordinal variable with subsequent points on the scale indicating increasing severity level of generalized anxiety expression (i.e. threshold GAD is more severe than subthreshold GAD and etc.). Ordinal logistic regression was performed to examine the association between the various levels of generalized anxiety expressions and socio-demographic factors (including age group, ethnicity, gender, marital status, education level, presence of chronic physical conditions, employment status, and income level). After adjusting for age group, gender, and ethnicity, multivariate logistic regression was used to calculate the odds ratios for comorbidity and impairment. Poisson regression was used to calculate the rate ratios of functioning days lost using data from the 30-day functioning module. 3. Results 3.1. Prevalence of worrying and GAD Prevalence estimates for the different levels of generalized anxiety expressions are presented in Table 2. Among the respondents, 5.7% reported worrying for at least one month (inclusive of more severe levels), 3.7% reported worrying for at least 3 months
(inclusive of subthreshold GAD and threshold GAD), 2.1% had subthreshold GAD (inclusive of threshold GAD), and 1.5% had threshold GAD. After applying DSM-IV hierarchy exclusion rules, 0.9% of respondents received a DSM-IV GAD diagnosis. Table 2 shows the association between generalized anxiety expressions and socio-demographic variables. Being younger, Indian, of “Other” ethnicities, divorced/separated, widowed, and unemployed significantly predicted more severe levels of generalized anxiety expressions. Those with primary education were less likely to have more severe generalized anxiety expressions than those with university education.
3.2. Comorbidity and impairment of worrying and GAD Table 3 shows the prevalence and odds ratios for comorbidity of lifetime mental illnesses and chronic physical conditions. The majority of respondents who worried for at least one month or had more severe levels of expressions (79.3%) had at least one of the disorders listed in Table 3. Prevalence of comorbid chronic physical conditions was higher than that of comorbid mental illnesses across all generalized anxiety expressions, except the threshold GAD category (any physical conditions, 49.4%; any mental illnesses, 78.8%). Major depressive disorder (MDD) was found to be the most common comorbid mental illness, and chronic pain was the most common physical condition across the generalized anxiety expressions.
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S.P. Lee et al. / Journal of Anxiety Disorders 32 (2015) 73–80
Table 2 Socio-demographic association with levels of generalized anxiety expressions. Worrying ≥1 montha 5.7% (1.9%)
Worrying ≥ 3 months 3.7% (1.6%)
Subthreshold GAD 2.1% (0.6%)
Threshold GAD 1.5% (1.5%)
Odds ratiosb
n
n
OR
95% CI
p-Value
Age group 18–34 82 35–49 39 50–64 24 65 + + 3 Ethnicity 37 Chinese 43 Malay Indian 58 Other 10 Gender 87 Male 61 Female Marital status 59 Single 78 Married 8 Divorced/separated Widowed 3 Education level 39 University Pre-U/Junior College/Diploma 33 22 Vocational 39 Secondary 13 Primary Pre-Primary 2 Any chronic physical condition 83 No Yes 65 Employment status 113 Employed 20 Economically inactive 10 Unemployed Below $19,999 $20,000–$49,999 Above $50,000 a b * **
71 48 22
%
95% CI
n
%
95% CI
%
95% CI
n
%
95% CI
3.17 1.47 1.28 1.26
2.2 0.8 0.5 0.0
4.1 2.1 2.1 2.9
43 37 13 6
2.27 1.68 0.65 1.42
1.4 0.9 0.1 0.0
3.1 27 2.4 19 1.2 10 3.1 0
0.79 0.87 0.34 –
0.3 0.3 0.0 –
1.2 1.4 0.7 –
53 48 21 0
1.76 1.95 1.22 –
1.1 1.2 0.4 –
2.4 2.8 2.0 –
1 0.7 0.4 0.3
0.5 0.2 0.1
1.2 0.8 0.9
0.2 0.007* 0.03*
1.79 1.80 2.93 4.18
1.2 1.3 2.2 1.6
2.4 2.3 3.7 6.8
33 28 27 11
1.61 1.18 1.37 4.32
1.1 0.7 0.8 1.7
2.2 11 1.6 17 1.9 23 6.9 5
0.52 0.70 1.17 1.60
0.2 0.4 0.7 0.1
0.8 1.0 1.6 3.1
29 35 53 5
1.37 1.45 2.63 2.09
0.9 1.0 1.9 0.2
1.9 1.9 3.3 4.0
1.0 1.0 1.5 1.8
0.7 1.1 1.1
1.4 2.0 3.1
1.0 0.004* 0.03*
2.38 1.53
1.7 1.0
3.1 2.1
58 41
1.85 1.37
1.2 0.8
2.5 23 2.0 33
0.43 0.81
0.2 0.4
0.7 1.2
48 74
1.22 1.78
0.7 1.2
1.7 2.4
1.0 1.0
0.7
1.4
0.9
3.08 1.45 1.65 1.66
2.0 1.0 0.0 0.0
4.1 2.0 3.5 4.6
28 57 10 4
1.47 1.27 4.94 4.03
0.7 0.8 1.3 0.0
2.2 21 1.7 32 8.6 2 8.4 1
0.89 0.51 1.00 0.12
0.3 0.2 0.0 0.0
1.4 0.8 2.8 0.4
37 66 17 2
1.48 1.21 7.42 0.18
0.8 0.8 2.9 0.0
2.2 1.7 11.9 0.4
1.0 0.9 4.5 3.3
0.6 2.4 1.2
1.5 0.8 8.4
