The travel cost method of economic valuation, travel cost analysis, or Clawson method is a revealed preference method of economic valuation used in cost–benefit analysis to calculate the value of something that cannot be obtained through market prices (i.e. national parks, beaches, ecosystems). The aim of the method is to calculate willingness to pay for a constant price facility. The technique was first suggested by the statistician Harold Hotelling in a 1947 letter to the director of the National Park Service for a method to measure the benefit of recreation.