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 For example, Carson and Mitchell (1995) describe an unpublished study of the value of reducing the risk associated with chlorination of drinking water.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.