Trends in solids/liquids poisoning suicide rates in Taiwan: a test of the substitution hypothesis

Data on age-, sex- and method-specific suicide rates for 1971-1993 in Taiwan were obtained. Changes in solids/liquids poisoning suicide rates were compared with suicide rates by hanging and other methods between 1983 and 1993.No concomitant increase in suicide rates by hanging or other methods was noted from 1983 to 1993, during which the suicide rates by poisoning with solids/liquids (mainly pesticides) decreased markedly and steadily. The phenomenon of method substitution was also not found by sex and age groups.In general, no method substitution was found along with the reduction in solids/liquids suicide rates in Taiwan. Our study results have also added the evidence that restricting access to methods maybe a promising strategy in preventing suicide, particularly in those countries where the "target method" has been found to contribute greatly to the suicide rates.A reduction in suicide rates after the launching of access restriction interventions was noted in several studies of suicide methods, involving domestic gases [1-3], vehicle emissions [4], prescriptions [5,6], pesticides [7] and guns [8-11]. However, a method substitution hypothesis has been proposed, in that a compensatory increase in suicide rates by other methods might be observed. Studies revealed that domestic gas might be substituted by car exhaust [3,12], gassing might be substituted by drug overdose [13], firearms might be substituted by jumping [8] or hanging [14], and car exhaust might be substituted by hanging [15] (see Table 1). However, all previous studies were done in Western countries and pesticides were not discussed in these studies.It is noteworthy that dominant suicide methods differ greatly across countries, particularly between Asian and Western countries. Poisoning with pesticides was the most common suicide method used by Asian people living in rural areas (notably China, Sri Lanka, Taiwan and India) [16]. Restricting access to pesticides was strongly suggested by the World Heal