spike command allows for a non-zero probability of zero willingness-to-pay in referendum-style contingent valuation experiments as suggested by Kristrom (1997). This property is particular usefull in experiments in which a large fraction of the population chose not to consume good being offered. In such circunstances the use of traditional parametric models based on probit and logit models are likelly to predict a negative willingness-to-pay.

Joao Pedro Azevedo, 2010. "SPIKE: Stata module to allow for a zero willingness to pay," Statistical Software Components S457126, Boston College Department of Economics.

Azevedo, Joao Pedro. What is the Value of Educational Broadcast? (February 2009). Available at SSRN: link

Kristrom, B. (1997). Spike Models in Contingent Valuation. American Journal of Agricultural Economics 79(3), 1013-1023.

This module should be installed from within Stata by typing "ssc install spike". Windows users should not attempt to download these files with a web browser.

spike; willingness to pay; zero wtp

João Pedro Azevedo
jazevedo@worldbank.org
World Bank
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