What is WBA?

Why-Because Analysis (WBA) is a rigorous technique for causally analysing the behaviour of complex technical and socio-technical systems. Its primary application is in the analysis of accidents, mainly to transportation systems (air, rail and sea). It is also used in the Ontological Hazard Analysis (OHA) method for safety requirements analysis during system development.

WBA is based on a rigorous notion of causal factor. Whether one event or state is a causal factor in the occurrence of another is determined by applying the Counterfactual Test. The Counterfactual Test was proposed by the philosophical logician David Lewis in 1973, who credited David Hume (1770's) and has withstood detailed philosophical criticism since. During analysis, a Why-Because Graph (WB-Graph or WBG) is built showing the causal connections between all events and states of the behaviour being analysed. The completed WB-Graph is the main output of WBA.

The WB-Graph provides a rigorous causal explanation of the behaviour being analysed. However, mistakes may be made in constructing the WB-Graph, as with any human activity. To detect such mistakes, WBA provides a formal proof method which can be used to check whether the WB-Graph is correct and relatively complete. The formal proof method is based on the logic EL, a multi-modal logic based inter alia on Lamport's TLA and Lewis's Causal Logic. Most users of WBA do not feel the need to check their WB-Graphs using the formal proof procedures, but for those who do, it is there. WBA is the only accident analysis method with such a formal consistency/completeness check.

Introductions to WBA

Self study material

We have the WBA workbook with example cases for students of WBA. The book was co-authored by Peter Bernard Ladkin, Jan Sanders and Thilo Paul-Stueve.

WBA examples

Examples of Why-Because Analyses are available from RVS and other sources. We list some publically available examples: