There is research in which the effects of quantitative variations appear to be
larger, though certainly not enough to satisfy economic theory. For example,
Carson and Mitchell 1995. describe an unpublished study of the value of reducing
the risk associated with chlorination of drinking water. They report that an
increase of risk from .004 to 2.43 annual deaths per 1,000 a factor of 600. yielded
an increase of SWTP from $3.78 to $15.23 a factor of 4.. This result does not
contradict the general conclusion of other research in this area: the response to
variations of scope is so slight that it is not explicable in the standard terms of
economic analysis.