1 Department of Social Medicine, National Yang-Ming University, Taipei, Taiwan.
2 Department of Health Policy and Management, Johns Hopkins Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, USA.
3 Institute of Health Care and Hospital Administration, National Yang-Ming University, Taipei, Taiwan.
4 Bureau of National Health Insurance, Taipei, Taiwan.
5 Academia Sinica, Taipei, Taiwan.
6 Institute of Public Health, National Yang-Ming University, Taipei, Taiwan.
Correspondence: Dr Yiing-Jenq Chou, Department of Social Medicine, School of Medicine, National Yang Ming University, 155 Ni-Long Street, Taipei, Taiwan 112, ROC. E-mail: yjchou{at}ym.edu.tw
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Abstract |
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Methods This population cohort study linked the National Health Insurance files, family registration, and death certificates. It consists of the 3 432 705 residents aged 15 years of central Taiwan, 19982000. They were stratified into victims (n = 301 327) and non-victims (n = 3 131 378). Victims refer to those who lost co-resident family members, were injured, or experienced property loss during the earthquake. Non-victims refers to all others. The suicide rate was calculated for the period 215 months after the earthquake. Adjusted odds ratios were estimated with logistic regression.
Results After adjusting for residential location, age, gender, major disease status, and level of urbanization, we found that victims were 1.46 times more likely than non-victims to commit suicide following an earthquake (95% CI: 1.11, 1.92).
Conclusions Given the large study population and individual information available to identify victim status, this study was able to detect a statistically significant earthquake effect on suicide rate. This effect on suicide might be diluted if only geographically based stratification were possible, as opposed to victim status stratifications. Mental health programmes or other preventive strategies might be more effective by specifically targeting victims rather than by simply targeting individuals living in earthquake-affected areas.
Accepted 15 July 2003
Natural disasters affect millions of people each year. Many are injured, or suffer the pain of losing loved ones, and the majority sustain property damage. A devastating earthquake rating 7.3 on the Richter scale hit central Taiwan in the early morning of 21 September 1999. It was the biggest earthquake since 1935, killing more than 2400 people, injuring another 11 000, and destroying 105 000 houses.1 For those surviving the earthquake, the aftermath was a dramatic life event. Causal pathways, leading from trauma to psychological consequences upon the death of a spouse or child,25 socioeconomic crisis,614 or physical disability and sickness,7,1317 have been extensively discussed in the literature. It suggests that the increase in stress (physical and emotional) and grief, the loss of social network, and the diminishing material support resulting directly or indirectly from traumatic events could increase the incidence of mental illness, and lead to suicidal ideation or completed suicides.2,9,1820
Even though some significant disaster-related effects upon mental health, such as depression and post-traumatic stress disorder (PTSD), have been identified, the impact of disaster on extreme post-traumatic responses by some victims, such as suicide, remains unclear.2140 To date, only a few papers have specifically studied the impact of earthquakes on suicide.39,40 The study by Krug and colleagues examined the association between suicides and earthquakes. Despite the large size of the affected population in their study they did not observe a positive relationship between suicides and earthquakes.39 Following the 1995 earthquake in Kobe, Japan, Japanese researchers stated that there was no increase in suicide rates among men after the earthquake.40 One possible explanation for these negative findings is that these two ecological studies observed earthquake-affected and unaffected areas at the county or regional level, as opposed to the individual victim level.
Since 1999, Taiwan has experienced a consistent increase in suicide rate (from 10.36/100 000 people in 1999 to 12.45/100 000 people).41 The earthquake and the financial crisis in Asia with the resulting economic recession could have contributed to this increase in suicides. Recently, a study by Taiwanese researchers indicated that significantly higher suicidal ideation existed among earthquake victims who had suffered injury to relatives, or destruction of property.30 This motivated us to use individual-level population data to follow up on victims of the 1999 Taiwan earthquake to observe actual occurrences of suicides. Individual-level data, and the large size of the study population allow us to advance existing knowledge about the association between earthquake and suicide, by comparing post-quake suicide rates of victims and non-victims, in addition to a pre-post comparison between affected and unaffected areas.
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Materials and Methods |
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Study population and record linkage
The study population includes 3 432 705 people aged 15 years living in the Taichung metropolitan area at the time of the earthquake, as identified through the government-maintained Family Registration file. This database provides relatively accurate demographic information on residents, such as age, gender, and the level of urbanization for each municipality.
Within the study population, death certificates were used to identify those who committed suicide during the study period. Suicide attempts are not identified in the available data and are therefore not included in the study. Death certificates, managed by the Department of Health in Taiwan, contain basic information on each deceased individual such as age, gender, date of death, and the underlying cause of death. Death certificates from 1998 to 2000 were used. Since it is a national registry of all deaths in Taiwan, we were also able to trace all deaths among study subjects who moved out of the central Taiwan area during the study period. About 0.1% of deaths could not be matched to a family registration record. The accuracy of suicide coding is relatively high, as all deaths resulting from accidents or violence (International Classification of Diseases, Ninth Revision, Clinical Modification E800E999) in Taiwan must be jointly confirmed by a district attorney and a forensic specialist (or coroner).
The other three administrative data setsthe Victims Data File, the Enrolment File, and the Major Diseases File, are managed by the Bureau of National Health Insurance (BNHI). The Bureau issued quake cards to the 301 327 individuals among the 3 432 705 residents who lost co-resident family members, were injured, or experienced property damage. This card exempted them from the cost-sharing amount required under the National Health Insurance programme (NHI). The Victims Data File tracks basic information on cardholders and allowed the identification of the victims from the overall population. However, no information regarding the severity of injury or property loss is available in the Victims Data File. The quake card recipients in this metropolitan area are referred to in this study as the victims. All remaining individuals in the study population are referred to as non-victims, and serve as the control group for the individual-level comparison in this study. Victims comprised 24% of the population in the affected area (272 786 victims/1 155 103 residents in the affected area = 0.24). However, not all victims resided in the affected area. A few collapsed buildings located in the unaffected area (46 municipalities) were found after the earthquake, although this area remained mainly undamaged by the earthquake. Victims only comprised 1% of the population in the unaffected area (28 541 victims/2 277 602 residents in the affected area = 0.01).
The Enrolment File was used to provide pre-quake socioeconomic and disability status information on the study subjects. NHI enrolment is mainly through employment wage tax deduction for people with a well-defined monthly wage, and through head-tax financing on farmers, fishermen, and people without a well-defined monthly wage. People with a well-defined monthly wage were classified into three categories: New Taiwanese Dollar (NT$)40 000, NT$20 000NT$39 999, and <NT$20 000. The results remained unchanged when classified into five or seven categories. People without a well-defined monthly wage were categorized into two groups: (1) agriculture and fishery workers, and (2) individuals that were enrolled in the BNHI through local government offices. The individuals who registered their residence as being in central Taiwan, but who enrolled through other BNHI branches, were classified into a different group. This pre-quake socioeconomic status (SES) variable had six categories in total. Dependants of those insured were classified in the same categories as the insured. As part of the welfare programme in Taiwan, the government provides a premium subsidy to individuals with physical disability, so therefore we were able to identify an individuals pre-quake physical disability status from the NHI enrolment file. The Major Diseases File was used to identify individuals with major diseases or injuries before the earthquake. In Taiwan, people with specific major diseases or injury can apply for a major disease/injury card. Cardholders are exempted from the cost-sharing required under the NHI programme. Based on the Injury Severity Index, the NHI major disease list includes 30 major disease or injury types such as cancer, end-stage renal disease, chronic psychotic disorder, cirrhosis of the liver, acquired immunodeficiency syndrome, and schizophrenia.42 This study used the ownership of a major disease/injury card to determine an individuals pre-quake health status. The individual characteristics (ownership of a major disease card, physical disability status, SES) of study subjects in September 1999 were used to represent their pre-quake characteristics.
The linkage of data sets was conducted by the Bureau using personal identification numbers and birthdays. About 2.8% of records in the NHI data could not be matched to a record in the family registration file. The administrative data sets are relatively more reliable than the NHI claims data. The final results remained the same after excluding those central region residents who were not enrolled in the Central Branch of the Bureau. This study was reviewed and funded by the BNHI. We have abided by the Bureaus strict regulations regarding data release and the protection of privacy and confidentiality.
Study period
We observed suicide rates from the pre-quake period (1 January 199820 September 1999) and the post-quake period (1 November 199931 December 2000). Since we were unable to distinguish victims from non-victims in October 1999, as the issuance of quake cards only started on 26 October 1999 and continued throughout the entire month, we excluded the month of October 1999 from the study period. Government assistance to quake card recipients took effect on 1 November 1999. Since death and emigration information for 1998 and 1999 are available in the Family Registration Data, this study was able to retrospectively calculate suicide rates in the pre-quake period.
Study design and statistical analysis
The study design for the area-level comparison is a pre-post design with a control group, and for the individual-level comparison it is a retrospective population cohort study. The data were structured such that there was one record per individual. One suicide event per 100 000 person-years was used to calculate the suicide rate for the area-level comparison. For individual-level analysis, logistic regression was used to estimate the odds ratios (OR) for suicide with the statistical program STATA. Given the low prevalence of suicide as a cause of death, OR will have the same value as rate ratios or relative risks.43
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Results |
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People with major mental diseases were 7.84 times more likely to commit suicide than people without mental diseases. People with physical disability had a significantly greater suicidal risk than people without such disability. More specifically, people with moderate disability had a higher risk than people with mild or severe disability. Little research has been done regarding suicide risk by severity of physical disability. Most studies use a dichotomous physical disability variable (severe disability versus all others or disability versus no disability) and find that physical disability is a strong predictor of suicides, especially among elderly people.4648 More importantly, after adjusting for all other factors, socioeconomically disadvantaged individuals had a higher risk of suicide than individuals with a higher SES. Also, people living in different urbanized municipalities had slightly different risks of suicide, which might be due to the socioeconomic environment of different neighbourhoods.
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Discussion |
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Several limitations should be noted. First, the impact of an earthquake on suicides seems to be smaller than other dramatic life stresses like the death of a spouse. Previous literature indicates that OR of loss of a spouse on suicides ranges from 3.91 for women to 4.09 for men.2 One plausible explanation could be that suicide risk varies according to the different life stresses (deaths of family members, injury, property loss) caused by an earthquake. More detailed information on victim criteria or severity level could help to test earthquake impacts on suicides by specific life stresses.
Second, the accuracy of suicide designations on death certificates might be a concern, since some suicides might be misclassified as accidental deaths. However, no study in Taiwan has validated the existence of either differential or non-differential misclassification in this regard. We have no way of validating the data due to privacy and confidentiality concerns. Third, selection bias might be a concern as an earthquake may not be a perfect instrument for randomization. If earthquakes do not strike randomly, non-victims might not be perfectly comparable to victims, and selection bias might have affected the results. Earthquakes tend to impact more heavily upon a higher risk population like people with lower SES or physical disability. In order to minimize possible selection bias, this study took pre-quake SES and health status into account. However, including only these variables might not be sufficient due to information validity and simplification problems associated with large administrative data sets.
Fourth, residual confounding by SES or other unmeasured factors might be a concern. Thus, we carried out additional analyses on the time pattern of post-quake suicides, assuming that the impact of an earthquake on suicide, caused by acute stress, grief, or material conditions is most likely to occur in the first 6 months.2,49 However, we found no strong early effect in the first 6 months (OR = 1.47, 95% CI: 0.96, 2.24 for the first 6 months; OR = 1.46, 95% CI: 1.02, 2.07 for after 6 months). Cultural factors may be one plausible explanation, as traditionally, the one year anniversary of the passing of a family member is a significant time, and may be a more appropriate cut-off point for this analysis. However, due to data limitation, we were unable to conduct the analyses. Follow-up studies with a longer post-quake mortality data available might contribute in this regard.
Finally, it is unlikely that an earthquake per se could cause suicides. Important mediators such as post-quake geographical hazards in earthquake-affected areas, and post-quake mental disorders, may also play an important role.
These results have important policy implications for post-disaster government interventions. Public health interventions undertaken by the government following an earthquake may have prevented some would-be suicides and thereby reduced the impact of an earthquake on suicides. Furthermore, previous literatures indicate that there are approximately 25 suicide attempts for every completed suicide, and that about 15% of people with depression commit suicide.39,50 Thus, based on these estimates, suicide may only represent a small portion of psychological problems after an earthquake. Preventive actions could be made more effective by focusing on the victim population instead of the general population in an earthquake-affected area. Our findings also suggest that it is essential for future research to take individual victim status and individual-level characteristics into consideration in order to fully uncover the impact of an earthquake on suicides.
KEY MESSAGES
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Acknowledgments |
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References |
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