Valuation is far from precise. Often it has to rely on indirect indicators – like the
value of property, which is likely to be greater in a ‘nice’ area (contingent valuation)
– to get an idea of what people are prepared to pay. Or focus groups and
questionnaires can be used to check what people value. Peoples’ values can rapidly
change with fashion, the general state of their national economy, and aesthetic and
religious outlook. A state can attach high value to something that would otherwise
be worthless if it is judged to be of heritage or strategic value. Environmental
valuation is also likely to vary between countries at different stages of development,
and in a given nation through history. It is also likely that in seeking agreement on
transnational issues there will be different views and priorities. So environmental
valuation is not absolute. Carson (2004) provides a bibliography and case studies of
contingent valuation use in over 100 countries.