Why–because analysis (WBA) 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
("from the earlier") and ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. knowledge is independent from current ex ...
) 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
Relation or relations may refer to:
General uses
*International relations, the study of interconnection of politics, economics, and law on a global level
*Interpersonal relationship, association or acquaintance between two or more people
*Public ...
between the factors.
WBA in detail
WBA starts with the question "What is the accident or accidents in question?". 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 newfound causes, and so on, until a satisfactory result has been achieved.
At each node (factor), each contributing cause (related factor) must have been
necessary to cause the accident, and the totality of causes must have been
sufficient to do so.
The formal tests
The ''counterfactual test'' (CT) – The CT leads back to
David Lewis' formal notion of causality and
counterfactuals
Counterfactual conditionals (also ''subjunctive'' or ''X-marked'') are conditional sentences which discuss what would have been true under different circumstances, e.g. "If Peter believed in ghosts, he would be afraid to be here." Counterfactual ...
. 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
*
Accident
*
Cause–effect graph
A causal map can be defined as a network consisting of links or arcs between nodes or factors, such that a link between C and E means, in some sense, that someone believes or claims C has or had some causal influence on E.
This definition could ...
*
Fault tree analysis
*
Five whys
*
Ishikawa diagram
*
Issue map
*
Issue tree
*
Root cause analysis
References
External links
Why-Because Analysis(WBA)
{{DEFAULTSORT:Why-because analysis
Causal diagrams
Debugging
Accident analysis
Directed graphs