In some cases, it is not possible to construct a counterfactual by creating a control group or a comparison group, but by constructing one logically.
This could involve using the baseline as an estimate of the counterfactual where it is reasonable to assume this would have remained the same without the intervention.
Process tracing can support this analysis at each step of the theory of change.
The following example comes from White, H., Sinha, S., & Flanagan, A. (2006). A Review of the State of Impact Evaluation Independent Evaluation Group, World Bank. Retrieved from website: http://www.oecd.org/dac/evaluation/dcdndep/37634226.pdf.
"Sometimes before versus after is valid for impact analysis since attribution is very obvious, so that there is no need for a comparison group. An example of this is the Finnish water supply project and its impact on time taken to fetch water. The time households spent in fetching water fell once water pumps were located in the village. There is no other feasible causal factor so the before versus after comparison tells us the actual impact."