Empirical practice in the recreation demand literature continues to rely on fraction-of-the-wage-rate assumptions to account for the opportunity cost of travel time. Using papers referenced in the chapter and any others you find relevant, complete the following:

(a) Inventory the different approaches researchers have used to measure the shadow value of time, both within and without the environmental economics literature. Provide an example citation for each.

(b) Based on your review propose an answer to the following question, and support it with findings from the literature: what fraction of the average wage rate should applied researchers use to best represent the opportunity cost of time in recreation models?