Background
Recent national epidemiologic studies have demonstrated a wide variation in the prevalence of anxiety-depression disorders across countries [
1‐
3]. Comparing immigrant populations from low and middle income countries (LMIC), to compatriots in their country-of-origin and the host population in their country of resettlement (typically high income countries; HIC), offers the potential to develop a greater understanding of the factors contributing to these differences in prevalence rates. Past studies in this field have been undertaken almost exclusively in North America, the focus being on Mexican and Puerto Rican (LMIC) immigrants to the United States [
4‐
6]. Immigrant populations have tended to display lower rates of anxiety-depression relative to the host society, and higher [
4,
6] or comparable [
5] rates to compatriots remaining in the source country. In the only study undertaken outside North America, the rate of anxiety-depression amongst Vietnamese immigrants was also found to be substantially lower than that of the host Australian-born population but higher than a Vietnamese source country sample [
7]. The present analysis will extend the findings of our studies amongst Vietnamese populations to investigate for the first time the nature and possible interactions of risk factors in determining the variation in inter-population prevalence rates.
Certain demographic and psychosocial risk factors for anxiety-depression appear to be universal, in particular, female gender [
8]; unemployment [
9]; lower levels of education [
10]; young (versus older) adulthood [
11]; comorbid substance use disorder (SUD) [
12,
13]; physical ill-health [
14]; exposure to potentially traumatic events (PTEs) [
15]; and in relevant samples, exposure to refugee-specific experiences such as political persecution and forced displacement [
15,
16]. An important question addressed in the present study is how these universal risk factors contribute to variations in inter-country anxiety-depression prevalence rates. First, we will examine the extent to which inter-country anxiety-depression prevalence differences are associated with variation in the quantity of exposure to risks such as unemployment, poor general health and high levels of trauma exposure [
17]. We will then further investigate whether there are ethno- specific risk factor patterns operating as a function of country-group [
18]. For example age has been found to operate differently between Hispanic vs. non-Hispanic groups in the United States, with older age being associated with mental disorder in the former group and younger age in the latter [
19]. If different risk factor patterns can be established when comparing an immigrant group to their host and source country populations, it will point towards the need to consider possible ecological, cultural and biological differences that may account for the variation in anxiety-depression between populations born in different countries [
2].
Ensuring the accurate measurement of anxiety-depression across cultures remains a ‘grand challenge’ in global mental health [
20]. There is growing recognition that standard diagnostic measures may be insensitive to culture-specific modes of experiencing and reporting psychiatric symptoms [
7,
21]. One strategy to address this challenge is to supplement standard diagnostic measures with indigenously-derived measures of anxiety-depression, an approach implemented in the present study. The disadvantage of adding a measure to the assessment of the source country and immigrant group (but not the host population) is outweighed by the risk of under-estimating the prevalence of disorders if only Western-derived measures are used [
22].
The present analysis draws on three community mental health surveys administered amongst: 1) Vietnamese refugee-immigrants settled in New South Wales, Australia; 2) a Vietnamese source country sample residing in the Mekong-Delta region of Cần Thơ City and Hậu Giang Province; and 3) the general Australian-born host population [
7]. The aim of the study was to compare the Vietnamese-immigrant group with the source and host samples in order to test whether (a) quantitative differences in risk factor profiles accounted for variation in anxiety-depression prevalence between the population groups; or (b) whether there are distinct interactions in risk factors based on country-of-origin or current residency.
Discussion
Our study aimed to examine factors underlying the consistent stepwise anxiety-depression prevalence rate patterns across host country populations (highest rates), resettled immigrant groups (intermediate rates) and source country populations (lowest rates). The findings provide evidence that risk factors vary not only in quantity between populations, but in their interaction based on the country-of-origin of the population. Risk factor profiles were similar between the Vietnamese-immigrant sample and the source Vietnamese population; but there were differences in the interaction of risk factors when comparing the Vietnamese-immigrant and the Australian-born samples. An analogous pattern has been observed for cross-national suicide rates, in which prevalence rates are largely constant between immigrants and their source country populations, but differ from those of the host society [
33].
Risk factors that were common to all populations included being female, unemployment, and having poor physical health, an observation that supports the universal importance of these influences. The two Vietnamese populations showed consistency in their risk factor profiles (analysis 1), with the differences being entirely quantitative in nature. Specifically, older Vietnamese-immigrants showed higher rates of PTE exposure, number of medical conditions and SUD diagnoses than their Mekong Delta compatriots — risk factors that in concert exerted a greater burden of anxiety-depression in that group. The pattern for PTE exposure is consistent with the general dose–response relationship with anxiety-depression disorders observed in other studies amongst refugee groups exposed to war and displacement traumas, including those involved in the Southeast Asian conflicts during the 1960-70s [
15,
16,
34,
35]. The higher rates of physical illness and SUD amongst older Vietnamese-immigrants may reflect the effects of exposure to war and the stress of forced migration.
In contrast, there was a marked difference in the pattern and interaction of risk factors between the Vietnamese-immigrant and Australian-born samples (Analysis 2). Age emerged as the key discriminator: the older cohort demonstrated higher rates of anxiety-depression in the Vietnamese-immigrant group; whereas the youngest cohort exhibited the greatest risk for anxiety-depression in the Australian-born sample. Older age also posed a greater risk in the Mekong Delta Vietnamese group (analysis 1). This contrast in age risk between both Vietnamese and Australian-born populations is consistent with other data from LMIC and HIC countries [
11,
36,
37], a finding that appears to be independent of the impact of medical disorders with advancing age [
36,
37]. It is vital therefore to explore further why age exerts such a powerful but variable influence on the prevalence of anxiety-depression across countries [
36].
PTE exposure was low and showed no association with anxiety-depression amongst young Vietnamese-immigrant adults, in contrast to the findings for the older Vietnamese-immigrants who were highly exposed to conflict-related trauma [
26]. Young Vietnamese-immigrants differed markedly from the young Australian-born cohort who reported higher levels of PTEs and showed greater vulnerability to their impact in relation to risk of anxiety-depression. It is possible that specific factors not measured in our study act to protect younger Vietnamese-immigrants from anxiety-depression, including greater constraints on the activities of young adults, a greater level of social interdependence and high levels of familial support [
38,
39]. These social factors may protect young adults from encountering traumas in the first instance, and buffer those who are exposed against any deleterious emotional impact. Young Vietnamese-immigrants may also be protected against developing SUDs by virtue of the same cultural protective influences, a possibility that is supported by other studies amongst young Asian immigrant samples [
40].
The present study adds important information to the debate regarding the universality or otherwise of the symptoms and determinants of common mental disorders such as anxiety-depression. Proponents of a universalistic position assert that disorders such as anxiety-depression are comparable across cultures, differing only in their surface manifestations [
2]. The opposing position holds that the origins and nature of disorders vary fundamentally across cultures and contexts [
41‐
43]. The findings reported here suggest that core risk factors may be universal, but their patterning and interaction may differ fundamentally across cultural and population groups. The findings also offer support to recent commentaries focusing on the diagnostic revisions in preparation for DSM-V, by demonstrating the importance of including culturally sensitive measures in assessing anxiety-depression disorders at a global level [
18,
21,
44]. Although adding an indigenous measure means that assessment protocols are not strictly commensurable across cultures, this strategy offers the advantage of ensuring that prevalence rates are not under-estimated through using only Western-derived measures, particularly amongst populations from East Asia [
22,
44]. Our indigenous measure showed a moderate level of concordance with the CIDI amongst the Vietnamese-immigrants, but at the same time identified cases not detected by that measure [
7]. Additionally, the risk associated with age remained consistent when the analysis was based on only CIDI diagnoses for the combined Vietnamese sample. Overall, the findings point to the value of combining indigenous and international diagnostic measures in transcultural comparative studies of this type.
Limitations of the study need to be acknowledged. First, the Mekong Delta represents just one region in a culturally diverse Vietnam; the site was selected because most Vietnamese-immigrants in Australia originate from the south of Vietnam. There would be benefit in replicating the findings in a nationally representative sample. There was a difference in the timing of the surveys forming the basis of the current analysis, with the Mekong Delta survey being undertaken more recently. We note, however, that if there was a process of secular shift, it would presumably have lessened differences between Vietnamese-immigrants and the Mekong Delta Vietnamese samples because of the recent acceleration of Westernization in Vietnam. Although response rates were high across all three samples, variation in participation may have influenced the proportion in each sample with and without anxiety-depressive disorders.
It was not possible to assess the specific impact of culture and migration experiences since these factors were only relevant to one group, the Vietnamese-immigrants. Clinical recalibration of the CIDI with other DSM–IV-based diagnostic instruments was not undertaken in the surveys included in the current analysis limiting definitive statements about the validity of the CIDI in assessing DSM-IV diagnoses in these populations. Studies undertaken among East Asian populations, including neighboring China, have identified adequate concordance between the CIDI and measures such as the Structured Clinical Interview for DSM–IV in settings despite recording similarly low prevalence estimates [
22].
Conclusions
The findings suggest that country-of-origin may exert a powerful impact on the interaction of common risk factors associated with anxiety-depression, an effect that persisted in the immigrant group even though it had resided in the host society for more than a decade. Further pursuit of this theme may throw important light on the origins and pathogenesis of anxiety-depressive disorders, and their expression and prevalence internationally. Age of risk is of particular importance, an issue worthy of further study given that there is evidence of a diametrically different pattern across populations from LMIC and HICs. In particular, if it is possible to determine why young adults from LMICs have such a low prevalence of anxiety-depression, that knowledge could be translated into improving prevention and intervention strategies for young adults in HICs who are at higher risk of developing these disorders.
Competing interests
The authors report no competing interests.
Authors’ contributions
BJL oversaw the analysis and interpretation of the data, and produced the initial and final manuscript. TC conducted the statistical analyses and assisted in interpreting the findings. DS contributed to the design of the Vietnamese-immigrant and Mekong Delta Vietnamese surveys, interpretation of analyses, and to the development of the manuscript. TTBP conducted and managed the Vietnamese surveys reported. MGN contributed to the design and acquisition of the Mekong Delta Vietnamese survey. ZS conceptualized the design and oversaw the implementation of the Vietnamese-immigrant and Mekong Delta Vietnamese surveys, and was substantially involved in the production of the manuscript. All authors have read and approved the final manuscript.