Estimating the benefits to Florida households from avoiding another Gulf oil spill using the contingent valuation method: Internal validity tests with probability?based and opt?in samples

This paper evaluates contingent valuation method data quality by examining differences in results between probability-based and opt-in internet samples using from a survey estimating passive use losses associated with the BP/Deepwater Horizon oil spill. Both pass internal validity tests of negative price (bid) coefficient positive sign on income but only sample passed scope test shows evidence values. We find that willingness to pay estimates may be over-estimated compared sample, though not statistically different. Results support utility less expensive samples.