title: Applying the Anderson-Darling test to suicide clusters: evidence of contagion at U. S. universities?
abstract: BACKGROUND
  Suicide clusters at Cornell University and the Massachusetts Institute of Technology (MIT) prompted popular and expert speculation of suicide contagion. However, some clustering is to be expected in any random process.
  
  
  OBJECTIVE
  This work tested whether suicide clusters at these two universities differed significantly from those expected under a homogeneous Poisson process, in which suicides occur randomly and independently of one another.
  
  
  METHODS
  Suicide dates were collected for MIT and Cornell for 1990-2012. The Anderson-Darling statistic was used to test the goodness-of-fit of the intervals between suicides to distribution expected under the Poisson process.
  
  
  RESULTS
  Suicides at MIT were consistent with the homogeneous Poisson process, while those at Cornell showed clustering inconsistent with such a process (p = .05).
  
  
  CONCLUSIONS
  The Anderson-Darling test provides a statistically powerful means to identify suicide clustering in small samples. Practitioners can use this method to test for clustering in relevant communities. The difference in clustering behavior between the two institutions suggests that more institutions should be studied to determine the prevalence of suicide clustering in universities and its causes.
authors.affiliation: Massachusetts Institute of Technology, <location>Cambridge, MA, USA</location>
authors.forename: Donald W
authors.initials: DW
authors.lastname: MacKenzie
mesh_terms: D016000:Cluster Analysis; D006801:Humans; D008404:Massachusetts / Q000453:epidemiology; D015233:Models, Statistical; D009518:New York / Q000453:epidemiology; D016012:Poisson Distribution; D013334:Students / Q000706:statistics & numerical data*; D013405:Suicide / Q000706:statistics & numerical data*; D014495:Universities / Q000706:statistics & numerical data*
keywords: Anderson-Darling; Poisson process; college suicide; suicide cluster; suicide contagion