Comparing water quality valuation across probability and non-probability samples

Abstract

We compare water quality valuation results from a probability sample and two opt-in non-probability samples, MTurk and Qualtrics. The samples differ in some key demographics, but measured attitudes are strikingly similar. For valuation models, most parameters were significantly different across samples, yet many of the marginal willingness to pay were similar across samples. Notably, for non-marginal changes there were some differences by samples: MTurk values were always significantly greater than the probability sample, as were Qualtrics values for changes up to about a 20% improvement. Overall, the evidence is mixed, with some key differences but many similarities across samples.