Errori di tipo ipotetico (hypothetical bias) nella stima del valore dei beni ambientali tramite la valutazione contingente

In the last decades contingent valuation method has been widely employed in order to estimate non-market goods as it can measure both use and non-use values. By selling the same good in an experimental and in a real market, some empirical studies found statistical evidence that hypothetical values are upward biased but others did not. The presence and the importance of the so called “hypothetical bias” could depend on the different experimental techniques, therefore some recent researches try to investigate the effects of such experimental settings by using a meta-analysis. In this paper, first of all, four meta-analysis studies were reviewed. The results of these studies are mixed with respect to the magnitude of the hypothetical bias and with respect to the factors that can mitigate it. In order to have some insight about the phenomenon under investigation, by using the same database of the most recent study, two different statistical model were estimated. The empirical findings suggest that the degree of over-revelation is influenced by the distinction between public vs private goods, the elicitation method, and the use of calibration instruments. I also highlight that the overstatement is quite severe in the case of public goods especially when they have a large hypothetical willingness to pay. On the other and, the statistical models show that the hypothetical bias could be remarkably reduced by using some calibration instrument.