Suicides are not purely stochastic events — one suicide can (and does) often influence others. Influence can extend not only to probability but also method of execution.
A recent example has occurred in Palo Alto, where a cluster has taken the lives of four students in the Palo Alto Suicide School District. All four died by suicide along the Caltrain corridor. A previous cluster of five suicides happened in Palo Alto in 2008-09.[http://www.theatlantic.com/magazine/archive/2015/12/the-silicon-valley-suicides/413140/ cite]
Cluster suicides are responsible for between 1 to 5% of all suicide deaths.[http://bit.ly/1PR9Qyo cite] Adolescents are most at risk.
The fact that this happened in Palo Alto twice within ten years makes it a rare incidence of an Echo Cluster.
Goffstown NH in the 1990s provides another example.[https://news.google.com/newspapers?id=jWAgAAAAIBAJ&sjid=umUFAAAAIBAJ&pg=3670%2C4182297 cite]
While most people think of suicides as the result of long reflection, the vast majority of sucides are impulsive. See Most Suicides Are Impulsive
A related issue is suicide contagion, which includes Media Influence on Suicide.