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Stated-Choice Design Factors Affecting Probability of Nontrading and Precision of Value-of-Time Estimates: Meta-Analysis of Individual Participant Data

The presented approach to stated-choice design takes into account the characteristics of real data, including nontrading responses and their possible effect on value-of-time estimates. A meta-analysis of individual participant data from 51 stated-choice surveys was undertaken to develop models of how characteristics of stated-choice designs affected the proportions of nontraders and the precision of value-of-time estimates. The modeling work confirmed tension between increasing the range of boundary values of time to be tested—reducing nontrading—and reducing the intervals between adjacent boundary values of time—increasing the precision of the value-of-time estimate. An optimization model was developed to find the parameter values for a distribution of boundary values of time that would maximize the expected precision of a value-of-time estimate, given a type of distribution and subject to a series of restrictions. The lognormal distribution was found to work well, and the nonlinear optimization problem could be solved quickly with a standard spreadsheet optimization tool. The optimization model produced a recommended set of boundary values of time that could be used as the starting point for stated-choice designs. The meta-analysis models could also be used to analyze stated-choice designs produced by other means, for instance, as a complement to the use of commercial efficient design software.