Testing the Validity of WTP values from a Contingent Valuation Survey in Portugal

This paper explores the statistical validity of the willingness to pay (WTP) answers from a contingent valuation (CV) survey concerning value assessment of recreation and biodiversity protection programs. Firstly, we use a non-parametric testing approach as to evaluate the whether (a) different information levels concerning the government costs with the Park and (b) different payment vehicles influence the stated WTP responses. Secondly, we use a parametric model specification as to investigate the impact of the elicitation question format on the stated WTP responses. The likelihood ratio test results, at 95% confidence level, confirm the validity of the proposed survey a measurement instrument. Nevertheless, the presence of free riding turns out to be statistically significant in one of the survey versions. The parametric model results suggest that the differences in the mean WTP estimates across the two question formats are not statistically different. Furthermore, the double bounded dichotomous choice model value estimates point out that the WTP for the recreation protection program is lower than the WTP for the biodiversity protection program, thus confirming the importance of non-use value component of the Natural Area.