I also think it is important that the evidence is used critically rather than uncritically. Again, a cyclic process allows this to happen more easily. If each step is preceded by planning and followed by review, learning by researcher and client is greater. The quality of evidence can also be increased by the use of multiple sources of evidence within all or most cycles. Differences between data sources, used critically, can then lead the researchers and the participants towards a deeper and more accurate understanding.
Literature can be such an alternative data source.
Use multiple cycles, with planning before action and critical analysis after it. Action research is a methodology whose flexibility allows learning and responsiveness. Vague beginnings can move towards better understanding and practical improvement through the critical analysis of the information, the interpretation of it, and the methods used. Good action researchers, I think, critique what they do and how they do it, the better to learn from the experience. It is the balance between critical reflection and flexibility which allows adequate rigour to be achieved even in confused field settings.