In epidemiology

Epidemiology

Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...

, a collider is a variable which is the effect of two (or more) other variables. It is known as collider because, in graphical model

Graphical model

A graphical model is a probabilistic model for which a graph denotes the conditional independence structure between random variables. They are commonly used in probability theory, statistics—particularly Bayesian statistics—and machine learning....

s, the other variables (which may not be associated) lead to the collider in a way that their arrow heads appear to collide on the same node that is the collider e.g.

The result of having a collider in the path is that a collider blocks the association between two variables, thus the two variables M and L with a collider P in between are independent of each other because the association between them is blocked by the collider variable P.

See also

• Causality
  Causality
  Causality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....
  
  
• Directed acyclic graph
  Directed acyclic graph
  In mathematics and computer science, a directed acyclic graph , is a directed graph with no directed cycles. That is, it is formed by a collection of vertices and directed edges, each edge connecting one vertex to another, such that there is no way to start at some vertex v and follow a sequence of...
  
  
• Path analysis