Using partial site aggregation to reduce bias in random utility travel cost models

We propose a "partial aggregation" strategy for defining the recreation sit es that enter choice sets in random utility models. Under the proposal, the most popular sites and sites that will be the subject of policy analysis e nter choice sets as individual sites while remaining sites are aggregated i nto groups of similar sites. The scheme balances the desire to include all potential substitute sites in the choice sets with practical data and model ing constraints. Unlike fully aggregate models, our analysis and empirical applications suggest that the partial aggregation approach reasonably appro ximates the results of a disaggregate model. The partial aggregation approa ch offers all of the data and computational advantages of models with aggre gate sites but does not suffer from the same degree of bias as fully aggreg ate models.