1.11 In assessing and delivering VfM it is also important to note that VfM is a relative concept which requires comparison of the potential or actual outcomes of alternative procurement options. This is reflected in the guidance with both Stage 1 and 2 assessments being based on a relative comparison between PFI and conventional procurement. This requires a high degree of estimation, especially where experience and/or data on similar projects procured under different procurement routes is limited. However, as markets change and mature, what may have been considered the most appropriate way to procure a project, or the best terms which could be achieved, may change. Therefore, care must be taken when comparing and benchmarking current situations to historical information and data.