The statistical investigation of the phenomenon of suicide began in the mid nineteenth century when data about suicide rates became available in all industrialized countries. Emile Durkheim's book about suicide which appeared in 1897 was a landmark in this research but there had been many earlier studies. The contribution of Durkheim stands out because he proposed a social interpretation of suicide rather than one based on individual, psychological factors. He maintained that one of the main factors of suicide is social isolation. According to this view it is the paucity of links and interactions with other people which leads to suicide. This perspective is similar to the interpretation of apoptosis according to which cell death occurs when the cells no longer receive the “stay alive” message from their neighbors (see the chapter on apoptosis).

Yet, to this day, the phenomenon of suicide remains fairly mysterious. Common sense seems to be misleading rather than helpful as illustrated by the two following observations. (i) Contrary to the assumption or expectation of many people, the monthly maximum of suicide rates does not occur in fall or in wintertime but in May or June. (ii) Even events as dramatic as the attack of September 11, 2001 have no visible impact on the number of suicides. This observation, which will be explained in more detail in a subsequent chapter, holds at monthly as well as at daily level.