Interventions

Intervention evidence can be set on discrete variables, continuous variables, and temporal variables (discrete or continuous).

Interventions

Using the example in the image above, an engine failing due to either Electrical Systems failing and/or a problem with the Fuel Supply is different to someone with malicious intent directly taking the engine offline. The later in the model above is an intervention, and it changes the way parent variables of the intervention receive information.

The intervention on Engine, stops the normal flow of information up through to the parents Electrical Systems and Fuel Supply. With standard evidence, these parents would change due to information flowing back up from Engine, making both an Electrical Systems error and a Fuel Supply error more likely, however an intervention blocks this flow. This makes sense because, under this model the engine failure does not make it more likely that fuel has run out ot the Electrical Systems having failed.

Another example would be in advertising. When customers purchase, having been purposefully exposed to advertising, this can also be modeled as an intervention.

Interventions are part of Do-Calculus. The generally accepted notation for a query on A, given an intervention on B is P(A | Do(B)).

Setting an intervention

  • Right click on a node, select Evidence and then Do(...)
  • Open the Evidence window and choose a drop down Do(...)

Temporal interventions

Temporal evidence can be set in the Evidence window. To set as an intervention, use the syntax Do(3.2) or Do(State1).

Interventions in the network viewer

When an intervention is set, a red outline will help identify it.