Efficiency versus bias: the role of distributional parameters in count contingent behaviour models
One of the challenges facing many applications of non-market valuations is to find data with enough variation in the variable(s) of interest to estimate econometrically their effects on the quantity demanded. A solution to this problem was the introduction of stated preference surveys. These surveys can introduce variation into variables where there is no natural variation and, as a result, natural experiments are not possible. The problem of no or insufficient variation in naturally occurring data to estimate the effects of interest has led to a large literature on stated preference methods.