page_title: Fast-and-frugal trees
section_title: Execution
hierarchical_section_title: Fast-and-frugal trees / How a fast-and-frugal tree works / Execution
caption_attribution_description: English: Figure 1. A fast-and-frugal tree&#160;that helps emergency room doctors decide whether to send a patient to a regular nursing bed or the coronary care unit (Green &amp; Mehr, 1997).
context_page_description: In the study of decision-making, including the disciplines of psychology, artificial intelligence, and management science, a fast-and-frugal tree is a type of classification tree or decision tree. As shown in Figure 1--which will be explained in detail later--fast-and-frugal trees are simple graphical structures that ask one question at a time. The goal is to classify an object into a category for the purpose of making a decision. Unlike other classification and decision trees, such as Leo Breiman's CART, fast-and-frugal trees have been defined to be intentionally simple, both in their construction as well as their execution, and operate speedily with little information. For example, the tree of Figure 1 only asks from one to maximum three questions.
  Fast-and-frugal trees were introduced and conceptualized in 2003 by Laura Martignon, Vitouch, Takezawa and Forster and constitute a family of simple heuristics in the tradition of Gerd Gigerenzer and Herbert A. Simon's view of formal models of heuristics.
context_section_description: To use a fast-and-frugal tree, begin at the root and check one cue at a time.  At each step, one of the possible outcomes is an exit node which allows for a decision (or action) -- if an exit is reached, stop; otherwise, continue until an exit is reached. you take an exit, stop; otherwise, continue and ask more questions until an exit is reached.
  Figure 1 illustrates a fast-and-frugal tree for classifying a patient as “high risk” of having a heart stroke and thus having to be sent to the “coronary care unit” or as "low risk” and thus having to be sent to a “regular nursing bed"   (Green& Mehr, 1997).
  Consider three patients, John, Mary, and Jack: 
  John has ST segment changes thus is classified as "high risk" and sent to the coronary care unit-- without considering other cues.
  Mary has no ST segment changes, does have chest pain as her chief complaint, but does not have any of the remaining five factors, thus is classified as "low risk" and sent to a regular nursing bed, after all three cues are checked.
  Jack has no ST segment change and does not have chest pain as his chief complaint, thus is classified as "low risk" and sent to a regular nursing bed, by considering these two cues.
caption: Figure 1. A fast-and-frugal tree that helps emergency room doctors decide whether to send a patient to a regular nursing bed or the coronary care unit (Green & Mehr, 1997) [GM].
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