Research report
A comparison of seasonal variation between suicide deaths and attempts in Hong Kong SAR

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Abstract

Background: Seasonal variations in suicide deaths and attempted suicides have been reported for many countries. Recent research has suggested that seasonal patterns of suicide deaths have diminished considerably. The seasonality pattern between attempts and completed ones are not the same. This paper is the first one to examine seasonal variation between suicide deaths and attempts simultaneously. Method: Census and Statistics Department and the Hospital Authority provided mortality and morbidity data on suicides for the period 1997–2001 in Hong Kong SAR, respectively. Seasonal patterns of suicide deaths and attempts were examined by a harmonic analysis and a non-parametric chi-square test. Results: A significant seasonal variation was detected in suicide attempts with a markedly bi-seasonal pattern was found amongst females with a peak in May and October; only a cyclic pattern was observed for males with a peak in summer. The female attempters who used non-violent suicide methods contributed to the second peak in October. On the other hand, there was no evidence of significant differences in the seasonal distribution among the suicide deaths for males and females. Only a mild pattern was found amongst females involving in violent suicide deaths, while others can be treated as a random event and no significantly pattern was observed in our study. Overall, a significant difference in seasonal variation existed between suicide deaths and attempts (p-value<0.01). Conclusions: This study reinforces the findings that seasonal variation in suicide appears to be diminishing. Also, suicide attempters and completed suicides in Hong Kong seem to arise from two non-identical but overlapping groups in the community.

Introduction

Many studies in West suggested a bi-seasonal pattern of suicides amongst female population while a cycle per year and no pattern was observed in males Parker and Walter, 1982, Micciolo et al., 1989. Seasonal variation does not only exist in suicide deaths but also amongst suicide attempts which is an act of potentially self-injurious with a non-fatal outcome, for which there is evidence of that the person intended at some level to kill himself/herself (O'Carroll et al., 1996). There was high association between these two data sets. Masterton (1991), Barker et al. (1994), De Maio et al. (1982), Bianco et al. (1998) and Preti and Miotto (2000) studied the subjects involved in deliberate self-harm and reported significance of seasonality of suicide attempts. Ho et al. (1998) suggested that social and cultural background distinction in Asian countries from West may help account for the difference in seasonality of suicide attempts. Seasonal variation in specific methods of suicide was found Rasanen et al., 2002, Ajdacic-Gross et al., 2003, Yip et al., 1998. The preference in adoption of suicidal method may be another key factor in accounting for the distinction in seasonal pattern of suicidal behavior Hawton et al., 1998, Ho et al., 1997.

Brewerton (1989) pointed out the existence of seasonality in serotonin functionality in human being, which regulates mood and impulse control in our brain and its activity in brain is sensitive to the change of climate. The correlation between serotonin functionality or mood disorder and suicide ideation/behavior may somehow help explain the seasonality in suicides or suicide attempts Malone and Mann, 1998, Atmaca et al., 2002, Maes et al., 1996, Morken et al., 2002. No clear seasonal pattern was reported in suicide deaths for both genders in Hong Kong Ho et al., 1997, Yip et al., 2001. This paper is the first of this kind to examine seasonal variation of suicide deaths and attempts simultaneously for the same period and to make comparison of their variation with respect to gender and method used.

Section snippets

Methods

Census and Statistics Department provided us with mortality data in HKSAR, whose death had received a verdict of suicide between 1997 and 2001. The Hospital Authority provided information on Accident and Emergency patients with diagnosis of deliberate self-harm upon admission and being admitted inpatients. All of suicide deaths and attempts method were classified and recorded according to the ICD-9 (WHO, 1978). The coverage of suicide attempters by the Hospital Authority is high though there is

Results

There were 4429 (1663 females and 2766 males) suicide deaths and 10,376 (6866 females and 3510 males) suicide attempts in Hong Kong between 1997 and 2001. Fig. 1 shows 3-month moving averages of the number of suicide deaths and attempts for each month for the period 1997–2001 separately. Suicide deaths appear to have a summer peak with an increasing trend (p-value<0.01). Also, a relatively consistent seasonal pattern holds amongst suicide attempts with a peak in early summer and a trough in

Discussion

Seasonality in suicide deaths and attempts has been extensively studied. However, it is the first paper to investigate seasonality of suicides and attempted suicides simultaneously. Seasonality between suicides and attempts is different. In an earlier study of seasonality of Hong Kong, clearly a cyclic pattern per year of suicides was reported in males and no bi-seasonal pattern observed amongst females with a tendency of diminishing in seasonal amplitude (Yip et al., 2001). The mild and

Limitations

The observed seasonality on suicide death and attempts are fairly robust, which is unlikely caused by the ascertainment bias through the Coroner's Court or Accident and Emergency Department of Hospital Authority (HKSAR). If the seasonality of suicide deaths and attempts for any particular groups are masked by the ascertainment procedures, it has to be postulated that the bias varies systematically with seasonality and operates in different ways of different gender, age groups or suicide

Acknowledgements

We are grateful to the two referees' for their useful comments, Census and Statistics Department, Coroner's Court and Hospital Authority of the Hong Kong SAR for providing the data of suicide death and attempts, respectively, for present study. The research is supported by the Hong Kong Jockey Club Charities Fund and Chief Executive Community Project.

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