Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
In contingent valuation surveys the category of zero bidders refers to individuals that are not willing to pay anything for the programme under analysis. Specific questions can help to identify true zero values, coming from people that are indifferent to the programme, separately from protest responses: the latter are generally excluded from the analysis. This paper introduces a mixture-sample selection model that takes into account both zero values and protest responses in the estimates. The model is applied to the valuation of a traffic calming scheme aimed at reducing risks for residents in three villages in the north-east of England.