In the case of primary goods, such as coffee, that are produced only in the less-developed countries and for which practically no substitutes exist, action to increase prices can easily be taken if demand is not too much affected by price increases.
Although an increased number of bone substitutes exist, autologous bone has to be considered as the most effective material for two-stage pre-prosthodontic augmentation in oral implantation.
The depletion of structural resources, such as hollow-bearing trees, within a landscape, may therefore be limiting to biota where no other functional substitutes exist.
This is a very useful and convenient theory, as long as the ceteris paribus assumption is not ignored, and it is understood that complements as well as substitutes exist for most traded goods, as Bierens and Swanson note [55].
For example, Company X's fish and chips would tend to have a relatively high elasticity of demand if a significant number of substitutes are available, whereas food in general would have an extremely low elasticity of demand because no substitutes exist.
Many substitutes exist for roofing as well as interior building walls and ceilings, including fiber-cement flat and corrugated sheet products that are made with polyvinyl alcohol fibers and cellulose fibers.
