Using a theory-based approach to evaluations allows us to forefront the assumptions that underpin causal chains from inputs to outputs and through to outcomes, intermediate states and impact. UN Environment evaluations are structured around a project or programme’s Theory of Change to assess the causal logic of the intervention and determine whether all external factors affecting outcomes, impact, sustainability and up-scaling have been carefully considered.

The Theory of Change of an intervention depicts the causal pathways from outputs through outcomes via intermediate states towards impact. The Theory of Change further defines the external factors that influence change along the major pathways i.e. factors that affect whether one result can lead to the next. These contributing factors are called drivers and assumptions. This approach has the benefit of incorporating the intended logic of an intervention into its implementation context.

Common definitions used in UN Environment are:

Outputs: Outputs are gains in knowledge, abilities and awareness  of individuals or within institutions, or the availability of new products and services that result from the completion of activities

Outcomes: the use (i.e. uptake, adoption, application) of a product or service by intended beneficiaries, observed as changes in behaviour, attitude or condition

Intermediate states: changes required in between project outcomes and impact, e.g. wide-scale adoption of improved natural resource management practices, country-wide shift towards renewable energy sources

Impact: Positive and negative long-lasting effects resulting from an intervention, directly or indirectly, intended or unintended. Impacts must relate to UN Environment's mandate

Drivers: external conditions necessary for project results to lead to next-level results, over which the project has a certain level of control e.g. strong support from other development partners in-country, public pressure on policy makers

Assumptions: external conditions necessary for project results to lead to next-level results, over which the project has no control e.g. turn-over of government officials, global financial situation, technological advances

The Theory of Change is represented in the evaluation report both as a narrative and diagrammatically. Although its primary use is to support an evaluation of effectiveness, the Theory of Change can be used to gain deeper insight into a wide range of evaluation criteria, such as sustainability or the quality of project monitoring etc.

Use of Theory of Change in project evaluations

Samples of Theory of Change diagrams


Likelihood of Impact Assessment

It is often not possible to measure actual impact of a project due to data and resource limitations, and the timing of the evaluation. To assess the likelihood of impact, UN Environment evaluations often rely on a theoretical approach based on the intervention’s Theory of Change called Likelihood of Impact Assessment. 

Assessment of Likelihood of Impact Decision Tree

Supplementary guidance notes on Impact Assessment