Why-Because analysis
Encyclopedia
Why–because analysis is a method for accident analysis
. It is independent of application domain and has been used to analyse, among others, aviation-, railway-, marine- and computer related accidents and incidents. It is mainly used as an after the fact (or a posteriori
) analysis method. WBA strives to ensure objectivity, falsifiability
and reproducibility of results.
The result of a WBA is a why–because graph (WBG). The WBG depicts causal relations between factors of an accident. It is a directed acyclic graph
where the nodes of the graph are factors. Directed edges denote cause–effect
relations
between the factors.
At each node (factor), each contributing cause (related factor) must have been necessary, and the totality of causes must be sufficient: it gives the causes, the whole causes (sufficient), and nothing but the causes (necessary).
formal notion of causality and counterfactual
s. The CT asks the following question: "If the cause had not been, could the effect have happened". The CT proves or disproves that a cause is a necessary causal factor for an effect. Only if it is necessary for the cause in question then it is clearly contributing to the effect.
The causal sufficiency test – The CST asks the question: "Will an effect always happen if all attributed causes happen?". The CST aims at deciding whether a set of causes are sufficient for an effect to happen. The missing of causes can thus be identified.
Only if for all causal relations the CT is positive and for all sets of causes to their effects the CST is positive the WBG is correct: each cause must be necessary (CT), and the totality of causes must be sufficient (CST): nothing is omitted (CST: the listed causes are sufficient), and nothing is superfluous (CT: each cause is necessary).
Accident Analysis
Accident analysis is carried out in order to determine the cause or causes of an accident or series of accidents so as to prevent further incidents of a similar kind. It is also known as accident investigation. It may be performed by a range of experts, including forensic scientists, forensic...
. It is independent of application domain and has been used to analyse, among others, aviation-, railway-, marine- and computer related accidents and incidents. It is mainly used as an after the fact (or a posteriori
A Posteriori
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) analysis method. WBA strives to ensure objectivity, falsifiability
Falsifiability
Falsifiability or refutability of an assertion, hypothesis or theory is the logical possibility that it can be contradicted by an observation or the outcome of a physical experiment...
and reproducibility of results.
The result of a WBA is a why–because graph (WBG). The WBG depicts causal relations between factors of an accident. It is a 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...
where the nodes of the graph are factors. Directed edges denote cause–effect
Causality
Causality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....
relations
Relation (mathematics)
In set theory and logic, a relation is a property that assigns truth values to k-tuples of individuals. Typically, the property describes a possible connection between the components of a k-tuple...
between the factors.
WBA in detail
WBA starts with the question what the accident(s) in question is(are). In most cases this is easy to define. Next comes an iterative process to determine causes. When causes for the accident have been identified, formal tests are applied to all potential cause-effect relations. This process can be iterated for the new found causes, and so on, until a satisfactory result has been achieved.At each node (factor), each contributing cause (related factor) must have been necessary, and the totality of causes must be sufficient: it gives the causes, the whole causes (sufficient), and nothing but the causes (necessary).
The formal tests
The counterfactual test (CT) – The CT leads back to David LewisDavid Kellogg Lewis
David Kellogg Lewis was an American philosopher. Lewis taught briefly at UCLA and then at Princeton from 1970 until his death. He is also closely associated with Australia, whose philosophical community he visited almost annually for more than thirty years...
formal notion of causality and counterfactual
Counterfactual
Counterfactual may refer to:* Counterfactual conditional, a grammatical form * Counterfactual subjunctive, grammatical forms which in English are known as the past and pluperfect forms of the subjunctive mood* Counterfactual thinking* Counterfactual history* Alternate history, a literary genre*...
s. The CT asks the following question: "If the cause had not been, could the effect have happened". The CT proves or disproves that a cause is a necessary causal factor for an effect. Only if it is necessary for the cause in question then it is clearly contributing to the effect.
The causal sufficiency test – The CST asks the question: "Will an effect always happen if all attributed causes happen?". The CST aims at deciding whether a set of causes are sufficient for an effect to happen. The missing of causes can thus be identified.
Only if for all causal relations the CT is positive and for all sets of causes to their effects the CST is positive the WBG is correct: each cause must be necessary (CT), and the totality of causes must be sufficient (CST): nothing is omitted (CST: the listed causes are sufficient), and nothing is superfluous (CT: each cause is necessary).
Example
See also
- AccidentAccidentAn accident or mishap is an unforeseen and unplanned event or circumstance, often with lack of intention or necessity. It implies a generally negative outcome which may have been avoided or prevented had circumstances leading up to the accident been recognized, and acted upon, prior to its...
- Accident analysisAccident AnalysisAccident analysis is carried out in order to determine the cause or causes of an accident or series of accidents so as to prevent further incidents of a similar kind. It is also known as accident investigation. It may be performed by a range of experts, including forensic scientists, forensic...
- Cause–effect graph
- Fault tree analysisFault tree analysisFault tree analysis is a top down, deductive failure analysis in which an undesired state of a system is analyzed using boolean logic to combine a series of lower-level events...
- Root cause analysisRoot cause analysisRoot cause analysis is a class of problem solving methods aimed at identifying the root causes of problems or events.Root Cause Analysis is any structured approach to identifying the factors that resulted in the nature, the magnitude, the location, and the timing of the harmful outcomes of one...
- Ishikawa diagramIshikawa diagramIshikawa diagrams are causal diagrams that show the causes of a certain event -- created by Kaoru Ishikawa . Common uses of the Ishikawa diagram are product design and quality defect prevention, to identify potential factors causing an overall effect...
- Five whys