Additionality

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Additionality is the property of an activity being additional by adding something new to the context. It is a determination of whether an intervention has an effect when compared to a baseline. Interventions can take a variety of forms but often include economic incentives.^[1]

Additionality may be evaluated ex post, as is often done in the practice of program evaluation, or ex ante, as an initial eligibility screen for issuing credits as part of an environmental or other public goods market.

For ex ante applications, additionality is evaluated for proposed activities. A proposed activity is additional if the recognized interventions are deemed to be causing the activity to take place, or whether a proposed activity is distinct from its baseline. A baseline is a prediction of the quantified amount of an input to or output from an activity resulting from the expected future behavior of the actors proposing, and affected by, the proposed activity in the absence of one or more policy interventions, holding all other factors constant (ceteris paribus).^[2]

Other working definitions of the term are available here.

For an example of the application of additionality in environmental crediting markets refer to carbon credits or carbon offsets.