Intervention Variables

Intervention Variables are those which an Actor plans to manipulate, to change.

The intervention Variable is marked with a green arrow in Diagrams. In most cases, like this, the Intervention is on a ((no,yes)) Variable, with the Intervention making the yes Level “factual” and the no Level “counterfactual”. So the default appearance of an Intervention is this:

A consequence

 !do An Intervention

!do

This is the more general version:

A consequence

 !do An Intervention *do it--do not do it* ((no,yes))

Translation: Intervention Variables are those which an Actor plans to manipulate, to change; the Level is set to the factual Level rather than the counterfactual Level, which is the Level which would have happened without the Intervention. If no Actor is mentioned, Theorymaker native speakers usually understand that the Actor is just “us”.

We can designate any Variable as an Intervention Variable by using the !do mark and, generally, specification of an ordered pair of Levels of the Variable called the Factual and Counterfactual.

If the factual Level of an Intervention Variable is something like “yes” and the counterfactual Level is something like “no”, they can be omitted, as can the designation of the Levels (((no,yes))). So the above diagram is equivalent to this:

A consequence

 !do An Intervention

We can abbreviate given that the Intervention Variable takes the factual Level with just “given the Intervention”.

Multiple Intervention Variables behave like just one

This

Outcome 1; Outcome 2

 !do Action A; !do Action B

… is equivalent to this …

Outcome 1; Outcome 2

 Action A ((no,yes)); Action B ((no,yes))

  !do Intervention

… in other words, you can have more than one intervention Variable in a Theory, but they behave as if they were driven by a single, background intervention Variable behind them. So it doesn’t make sense to say “we’ll do Intervention A but maybe we won’t do Intervention B”.

Later xx we will look at Interventions by different Actors.

Intervention Variables are effectively root Variables

Do these “do” arrows necessarily have to be only at the beginning of some kind of delivery chain? If an agency feels it has almost full control over more than one link in the chain, there’s no reason why they shouldn’t be designated as such?

Skills available 

 !do Skills retained 

  !do Skills trained 

Intervention Variables will in general be root Variables, i.e. Variables with no more Variables upstream of them. While it is perfectly possible to intervene at some Variable in the middle of some Theory, doing so eliminates the influence of all upstream Variables (Pearl 2000) and so those upstream Variables take no further part in the Theory of Change.

An intervention on a child deletes its parents.

References

Pearl, Judea. 2000. Causality: Models, reasoning and inference. Cambridge Univ Press. http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=153246.