Handling Intra - Household Correlations in Modeling Travel : 1 a Comparison of Hierarchical ( Random Effect ) Models and 2 Marginal

1 In this paper, the necessity for treating intra-household correlation is investigated by analyzing 2 two travel behavior indices, i.e. travel time and travel distance, for three important travel motives 3 (commuting, shopping, and leisure). Data stemming from the 2010 Belgian National Household 4 Travel Survey are used in the analysis. Two model approaches that accommodate for intra5 household correlation are compared, namely the generalized linear mixed model (GLMM) and 6 GEE model approach. Both model approaches show that high levels of intra-household 7 correlation are present, and therefore the use of models that take into account intra-household 8 correlation, is strongly recommend. Results indicate that this requirement is the most urgent for 9 non-commuting trips. Moreover, the results show that GLMM and GEE yield comparable 10 estimates in the case of normally distributed data. Furthermore, evidence was provided that the 11 more the estimates of the intra-household correlation provided by the two approaches differ, the 12 less the homogeneity of the parameters is assured. In this regard, if one has to choose between 13 the GLMM and GEE methodology, especially the negative consequences of choosing an 14 inappropriate covariance model in the case of a GLMM model favor the selection of the GEE 15 methodology. Further research is needed to compare the two approaches in the context of non16 normally distributed travel behavior data. 17 18