Discussion
We found that depression, PTSD and other anxiety disorders were associated with reduced QOL among Norwegian tsunami survivors. This is consistent with other studies of natural disaster survivors [
22,
23]. In particular, depression seems to exert a broad negative effect on QOL, including overall measures of perceived QOL and health satisfaction. This finding is in agreement with many epidemiological studies [
38,
39] and clinical studies [
40]. However, there is no clear evidence in the literature that depression consistently has a more pronounced negative effect on QOL compared to other psychiatric disorders. It appears as though the disorder severity and its longitudinal course determine the associated reduction in QOL rather than a particular psychiatric condition per se [
41]. In addition, due to the significant comorbidity between depression and PTSD in the current study, the role of PTSD may have been underestimated.
PTSD seems to have a significant negative effect on certain aspects of QOL, including psychological health, social relationships, and environment. The negative effect of PTSD or posttraumatic stress on elements of environment-related QOL is documented in previous disaster studies [
19,
42]. Still, we found these effects rather surprising, as Norwegian tourists were repatriated within a short time to stable home communities [
43,
44]. Environment-related QOL includes items such as financial resources, physical safety and security, health and social care, home environment, new opportunities, opportunity for recreation, physical environment, and transportation, which are likely to be negatively affected in the aftermath of a large-scale disaster. Thus, as the majority of our population escaped most of these secondary disaster stressors, one would expect a reduced impact of disaster exposure and subsequent PTSD symptoms on environment-related QOL.
The strong negative relationship between psychiatric disorders and psychological health- and social relationship-related QOL was expected, as poor mental health is likely to affect these domains [
45]. The adjusted model showed that depression exerted the main negative effect on psychological health, whereas other anxiety disorders had the most significant effect on social relationships. One possible explanation for this finding might be that social relations were strengthened within the families after the tsunami, especially in depressed people. A previous study of Norwegian parents who experienced the 2004 tsunami reported an increase in family care and appreciation for family values [
46]. These changes remained stable 2 years after the tsunami and are likely to have occurred in our population, as many of the participants lived within a family constellation with children. Such strengthened family cohesion may have buffered the likely negative effect of depression on social relationships.
Of the psychiatric disorders, physical health-related QOL was only related to depression and remained significantly related to depression after adjustment for other psychiatric disorders. One explanation could be that the measure of physical health contains items that overlap with depression, i.e., activities in daily living, energy and fatigue, sleep, pain, and work capacity. Of note, pre-disaster physical health was generally good in the current study population and few suffered severe injury [
29], which reduces the possibility of overlap between a severe somatic condition and depressive symptoms.
The prevalence of specific phobias was relatively high, but this condition was not significantly related to QOL. We have previously shown that specific phobias had little negative impact on socio-occupational functioning among Khao Lak survivors compared to depression and PTSD [
29]. The psychopathological effect of specific phobias in disaster populations seems to be relatively mild, as survivors can avoid phobic exposure related to specific situations without having any major impact on their daily life activities.
We did not find a negative effect of substance disorders on QOL. Although there has been less focus on QOL in the addiction field, available evidence suggests that QOL is generally poor among active substance abusers and treatment seekers [
47,
48]. However, the majority of those who were diagnosed within this cluster/group in the present study did not have a severe form of substance abuse or dependence. In addition, the use of MINI may lead to an over-diagnosis of alcohol and substance misuse in non-clinical settings.
We used the two general items from WHOQOL-BREF to assess any changes in QOL over time. We found no change in the overall score for perceived QOL and health satisfaction from 2 years to 6 years after the tsunami. However, we found that psychiatric morbidity showed an overall increase in explained variance for both perceived QOL (51 to 62 %) and health satisfaction (22 to 52 %) from 2 to 6 years. All of the predictors were measured 2 years after the tsunami and more than 3 years before the last measure of QOL. Thus, we expected a decrease in the relation between psychiatric morbidity and QOL over time, as posttraumatic stress and other psychopathology tend to decrease with time after disasters [
49,
50]. In addition, a correlation tends to weaken as the time between the measurements increases. One interpretation of the present finding may be that individuals who recover experience an increase in QOL, whereas individuals who do not recover experience either an increase in symptom level and subsequent poorer QOL or merely a negative change in perception of QOL with time [
51,
52]. We cannot rule out that other variables, i.e. changes in socioeconomic status and aging process, may have contributed to strengthen the relationship between psychiatric morbidity and QOL over time. Another finding that supports the idea that changes occurred from 2 to 6 years post-disaster is that both PTSD and depression showed a reinforced negative relation to perceived QOL from T1 to T2. A similar change also occurred between depression and the construct of health satisfaction in QOL.
We believe that development of chronic mental illness may lead to a worsening of QOL due to deterioration of social relations, inappropriate use of own personal resources, apostasy from work, and increasing social isolation [
52]. A study of earthquake survivors showed that QOL was worsened with time among those who received less relief support in the aftermath of disaster [
53]. This may be opposed to chronic somatic conditions, for which many persons successfully adapt to symptoms, maintain social relations and are able to focus on their personal resources [
54]. However, some studies also indicate that long-lasting depression may have debilitating effects on work and psychosocial functioning even after significant reduction in depressive symptoms [
39,
54,
55]. As work and psychosocial functioning are closely linked to QOL, we cannot rule out the occurrence of the latter among some of the persons in the population.
Methodological considerations
There are some limitations in the study. The small sample size yields low power for many of the analyzes. This suggests that caution must be made regarding the conclusions. In addition, the relatively small sample size limited detailed analyses i.e. of all the individual psychiatric disorders and other subgroups, as the results would have been more uncertain and difficult to interpret. Although we achieved a high response rate, there is still possibility of selection bias, as the main reason for not participating was lack of time, meaning that non-participants had a busy life, which may indicate a good quality of life and a good mental health. However, it is unclear how this assumption may have affected our results. The majority of the sample had at least one other family member experience the trauma with them which may have facilitated a feeling of strengthened social support and thereby influenced the results.
Telephone interviews were conducted in the 6-year follow-up compared to face-to-face interviews in the 2-year study, which could have affected the results. However, telephone interviews are often used in epidemiological research and are a valid method of assessing structured information such as axis I psychiatric disorders [
56].
Generally, the present findings may be limited to populations that experience traumatic events with a sudden impact and relatively brief exposure and may not be applicable to other populations that are exposed to chronic stressors. One may also argue that this sample of Norwegians, having the possibility to spend their Christmas holiday abroad, may represent a more privileged sub-population of the Norwegian population. It is previously described that The Norwegian tourist population that experienced the tsunami did not differ from the general Norwegian population with regard to employment and marital status [
57], though they had a higher than average education level and family constellation with children, which may indicate higher than average levels of socioeconomic status.
It is suggested that the prevalence of psychopathology documented in studies after natural disasters is generally lower than that documented after man-made disasters [
50]. However, in studies of natural disasters it is more difficult to explicitly identify groups of persons who can be considered direct victims. Natural disasters often affect large areas and the study samples predominantly include persons from a broader area affected by the disaster. When studying persons who were in the more heavily affected areas at time of the disaster, like our population, higher prevalence’s of psychopathology are reported [
58,
59].
The measure of QOL at T2 was restricted to perceived quality of life and health satisfaction measured with two single questions. This limits a thorough understanding of changes observed in the relation between psychiatric morbidity and QOL.
There are several strengths in the study. We achieved a relatively high response rate at T1 and the attrition rate between T1 and T2 was low, reducing the risk for bias. We used structured clinical interviews to detect a broad range of psychiatric conditions rather than covering a few disorders through self-reported questionnaires. We asked additional questions for the most relevant psychiatric disorders in order to follow the trajectories of these conditions. The study population was rather homogeneous due to the nature of the travel regarding work, family, finance, and physical and mental health. The relatively fast evacuation of the Norwegian tourists reduced the impact of secondary disaster stressors, limiting the impact of trauma to the primary tsunami experience. Finally, regardless of impairment level, the present sample received affordable and easily accessible medical and psychiatric care as well as ample community support [
60,
61].