Spatial patterning of suicide
Taiwan's urban region includes most of the western part of the island, with four major cities - Taipei in the north, Taichung in middle Taiwan, and Tainan and Kaohsiung in the southwest; population aged 15+ in these four cities was 2 176 000, 815 000, 617 000 and 1 244 000 respectively. Hualien (population aged 15+ = 87 000) is the only city in East Taiwan, which otherwise comprises mostly rural and mountainous areas.
Between 2002 and 2009 there were 36 110 suicides in Taiwan; 4913 (13.6%) of these were pesticide poisonings. 3950 (80.4%) of the pesticide deaths were certified as suicides, 639 (13.0%) as undetermined deaths and 324 (6.6%) as accidents. The proportion of males among the pesticide suicides (71.7%) was similar to that for non-pesticide suicides (68.2%), though pesticide suicides tended to be older (mean age 55.1 years) than non-pesticide suicides (mean age 47.7).
In 2002-2009 pesticide poisoning was the third most commonly used method in Taiwan, following hanging (30.2%) and poisoning using non-domestic gases (25.0%); pesticide poisoning accounted for 69% of all suicides from poisoning using solid or liquid substances. Table summarizes the distributions of pesticide, non-pesticide and overall suicides and the area characteristics investigated across the 358 Taiwanese districts. Raw (unsmoothed) SMRs for pesticide suicides showed a striking 65-fold difference (90% range 0.08-5.18) even when the most extreme 10% values were excluded. There was also a marked 22-fold difference in smoothed SMRs (90% range 0.20-4.49). In contrast, non-pesticide suicides showed much less spatial variation; unsmoothed and smoothed SMRs showed 2.5-fold (90% range 0.55-1.40) and 1.6-fold (90% range 0.78-1.21) differences respectively.
Number of suicides, raw standardized mortality ratios (SMRs), smoothed SMRs and area characteristics across Taiwan's 358 districts
As shown in Table , the mean and median of raw and smoothed SMRs for pesticide suicides were higher than one (i.e. the national average); this was because a large number of districts (mostly rural) with small populations showed higher than the national average rates while a smaller number of districts that were urban and had much larger populations showed lower than the national average rates.
Figure shows the geographic distributions of smoothed SMRs for (A) pesticide suicide, (B) non-pesticide suicide and (C) overall suicide. The patterns for unsmoothed SMRs were similar but somewhat less clear due to unstable estimates in sparsely populated areas (data not shown). Higher rates of pesticide suicide were found in East and Central Taiwan, with a concentration of the highest rates in the most rural areas (Figure ). One hundred and thirty (36.6%) districts had a SMR above two; they accounted for nearly half (46.6%) of all pesticide suicides, but only 13.4% of Taiwan's population aged 15+ live in these areas. In contrast, five major cities showed the lowest rates; they covered 26.8% of overall population but accounted for only 6% of pesticide suicides.
Figure 1 Mapsa for (A) pesticide, (B) non-pesticide and (C) overall suicideb across Taiwan's 358 districts, 2002-2009. aSmoothed standardized mortality ratios (SMRs) were mapped here. bIncluding certified suicide, undetermined death, and accident from pesticide (more ...)
In contrast to the distinct geographic pattern of pesticide suicide, there was no strong spatial patterning for non-pesticide suicide, although above average rates were found in Kaohsiung city and some areas surrounding Taipei city (Figure ). The geographic distribution of overall suicides (Figure ) was more similar to that of pesticide suicides than non-pesticide suicides, indicating the impact of pesticide suicide on the overall spatial patterning of suicide in Taiwan.
In the sensitivity analyses including certified suicides only, the main features of the spatial patterning of pesticide, non-pesticide and overall suicides were similar to those based on data for certified and possible suicides combined (data not shown).
Overall suicide rates were higher in rural than urban areas (25.6 versus 22.8 per 100 000) in Taiwan. Table shows rural and urban rates of suicide and their differences by suicide method. The differences in overall suicide rates between rural and urban areas were mostly attributable to pesticide suicide - the rural-urban difference in pesticide suicide rates was 5.4 per 100 000 (7.0 versus 1.6 per 100 000), while for other methods differences ranged from 0.4 per 100 000 for hanging (7.4 versus 7.0 per 100 000) to -1.4 per 100 000 for jumping (1.6 versus 3.0 per 100 000). There was a substantial gradient in pesticide suicide rates across the seven categories of urbanization - rates were 0.5, 1.6, 2.9, 5.4, 6.7, 10.9 and 8.7 per 100 000 for areas in level 1 (most urban) to 7 (most rural) respectively (Table ). Nearly two thirds of pesticide suicides (65.1%) were in rural areas (levels 4-7), yet these areas included only 28% of Taiwan's population aged 15+ years. In contrast, non-pesticide suicide rates showed much less variations - they ranged from 21.8 (level 3) to 17.6 (level 7) per 100 000 (Table ).
Age-standardized suicide rates per 100 000 in rural and urban areas in Taiwan, 2002-2009
Ecological analyses showed that a district's pesticide suicide rate was strongly associated with the proportion of the workforce involved in agriculture (Table ). Figure shows the maps for the proportions of workforce involved in agriculture, lone-parent households and median household income across Taiwan's 358 districts in 2000. In the unadjusted model, one standard deviation increase in the proportion of workforce in agriculture was associated with a 78% increase in district rates of pesticide suicide (rate ratio [RR] = 1.78, 95% Credible Interval [CrI] 1.63-1.94), although the strength of association decreased after controlling for an area's levels of lone-parent households and median household income (RR = 1.58, 95% CrI 1.44-1.74). When additionally controlling for area levels of divorced/separated population and population mobility in a sensitivity analysis, the strength of the association further decreased (RR = 1.46, 95% CrI 1.31-1.61). In another sensitivity analysis that additionally controlled for an area's level of population density, the association of pesticide suicide rates with the proportions of workforce involved in agriculture attenuated markedly (RR = 1.24, 95% CrI 1.10-1.38), but this may be an underestimate as population density was strongly correlated with an area's level of agricultural workforce (Pearson correlation coefficient = -0.73) and likely to be a partial indicator of agricultural workforce and exposure to pesticides in itself.
Rate ratios (and 95% Credible Intervals) of suicide per SDa increase in three area characteristics
Mapsa for (A) agricultural workforce (%), (B) lone-parent households (%) and (C) median household income. aAccording to standard deviation (SD) away from the national mean, across Taiwan's 358 districts, 2000.
In contrast, rates of non-pesticide suicide were lower in districts with a higher proportion of workforce involved in agriculture (unadjusted RR = 0.93, 95% CrI 0.90-0.96; adjusted RR = 0.91, 95% CrI 0.87-0.95). Overall suicide rates were positively associated with an area's level of agricultural workforce (unadjusted RR = 1.09, 95% CrI 1.06-1.13; adjusted RR = 1.06, 95% CrI 1.03-1.10), although the strengths of associations were much weaker than those for pesticide suicide.
In the sensitivity analyses including certified suicides only, results were similar to those based on certified and possible suicides combined (detailed data not shown). In the models controlling for lone-parent households and median household income, districts where a higher proportion of population worked in agriculture had higher rates of pesticide suicide (adjusted RR = 1.76, 95% CrI 1.48-2.09), lower rates of non-pesticide suicide (adjusted RR = 0.92, 95% CrI 0.87-0.99) and higher overall suicide rates (adjusted RR = 1.09, 95% CrI 1.03-1.16).