The first step of a global or regional survey is to compile an appropriate listing of operating plants for that product. Sometimes a set of operating data will exist already, and this can be used as a starting point. In other cases, the plants will have to be contacted to encourage them to submit operating data. Unless all of the plants in the selected region are mandated to participate by a government authority, participation will be voluntary and some companies will elect not to participate. Old and small plants, which the owners know to be noncompetitive, often choose not to participate. This voluntary study may even exclude some regions that would be interesting but where the producers do not want to participate. Communication or other issues can also arise, especially if local authorities have already made public comparisons that discourage certain producers from participating.
As a result, the plants included in a survey can often end up being mainly in
certain regions, with only the larger and more modern plants represented. Technology
differences, plant perimeter, and local factors may have to be considered, using sound
normalization practices and engineering judgment