sentence1: In order to investigate the impact of using the CV based WTP estimates, the Alternative Estimate relies on a value for incidence of chronic bronchitis using a cost-of-illness estimate based Cropper and Krupnick (1990) which calculates the present value of the lifetime expected costs associated with the illness.
sentence2: In 1990, Cropper and Krupnick conceived a way to estimate cost-of-illness.