Sample Selection Model for Protest Votes in Contingent Valuation Analyses

15 Pages Posted: 6 Jun 2000

See all articles by Pinuccia Calia

Pinuccia Calia

Universita di Cagliari - Department of Economics

Elisabetta Strazzera

Universita di Cagliari

Date Written: July 1999


Respondents of contingent valuation surveys may place a null value on the public good, for reasons that differ from a genuine indifference to the good, but that can be interpreted as a "protest": either against the interview, or the public management, or both. A good survey design can effectively reduce them, but protest votes can hardly be completely removed from the dataset, and, if there is sample selection bias, they lead to biased estimates for the wtp measure. We propose a survey design, and a sample selection model, that allows taking into account, and correcting, the possible bias due to protest votes. Since the asymptotic standard errors estimated by means of the inverse of the information matrix containing the sample selection parameter are not reliable, we use an alternative procedure based on the likelihood profile. It will be seen that sample selection models may present estimation problems because of the flatness of the likelihood function: in some cases confidence intervals around the sample selection coefficient are too wide to give evidence of presence or absence of sample selection bias. We maintain that even in these circumstances the sample selection model with the protest votes should be preferred to the model without protest votes, since it takes into account the uncertainty about the estimates of the willingness to pay for the public good.

Keywords: contingent valuation, protest votes, sample selection bias, survey design, likelihood profile, sample selection parameter

JEL Classification: C35, C51, C81, D60, H41, Q26

Suggested Citation

Calia, Pinuccia and Strazzera, Elisabetta, Sample Selection Model for Protest Votes in Contingent Valuation Analyses (July 1999). FEEM Working Paper No. 55.99. Available at SSRN: or

Pinuccia Calia

Universita di Cagliari - Department of Economics ( email )

V. S. Ignazio 17
Cagliari 09123, CA 09123

Elisabetta Strazzera (Contact Author)

Universita di Cagliari ( email )

CRENOS and DRES Via Fra Ignazio, 78
I-09123 Cagliari
+39 070 675 3763 (Phone)
+39 070 675 3760 (Fax)

Register to save articles to
your library


Paper statistics

Abstract Views
PlumX Metrics