The study draws as much as possible on impact assessment studies of existing schemes. However, the
availability of studies in relation to the various different labels and standards is sometimes limited.
There are many methodological difficulties associated with in-depth impact assessment, and analytical
assumptions may be required in the extrapolation of study findings to derive overall expected
development impacts. It was beyond the scope of this study to undertake independent impact
assessments on each of the labelling schemes being analysed.