Cook, T.D. (2000). The false choice between theory-based evaluation and experimentation. New Directions in Evaluation, 87, 27-34.
"Few program theories specify how long it should take for a given process to affect some proximal indicator in the causal chain. But without such specifications, it is difficult to know when disconfirmation occurs, whether the next step in the model has simply not occurred yet or instead will not occur at all. It is this ambiguity about timelines that allow program developers who have been disappointed by evaluation results to claim that positive results would have occurred had the evaluation lasted longer. But because such theories are not typically available, the argument is often heard when developers do not like what the evaluation reports." (30)
This has a very practical impact on WHEN to implement specific elements of an evaluation and on the EVALUABILITY of a project or program at any specific point in time.
To address this problem:
Sridharan, S., Campbell, B., & Zinzow, H. Developing a Stakeholder-Driven Anticipated Timeline of Impact for Evaluation of Social Programs, American Journal of Evaluation, Vol. 27, No. 2, June 2006.
In the absence of a clearly spelled out theory of the timeline of impact(s), the authors suggest a methodology for developing such a timeline based on stakeholders' expectations. In other words, the project stakeholders may be in the best position to estimate when the project's impacts will be felt.