Examining the effects of residential self-selection on internal and external validity: an interaction moderation analysis using structural equation modeling

Empirical studies on the land use–travel relationship have begun to consider the confounding or moderating effect of residential self-selection on the relationship. The studies were mainly focused on how to control for selection bias in relation to its threat to internal validity, but the bias also harms external validity through its interaction with explanatory variables. This study further considers this interaction moderation using partial least squares structural equation modeling, which compared to its covariance-based counterpart, can easily specify a large number of interaction indicators and include both reflective (compact land use) and formative (life situation inclined to automobile travel) constructs. Tested in Seoul, South Korea, structural equation models find that a considerable proportion of the land use effect on travel time is attributed to the self-selection. Regarding the interaction moderation, it turns out to significantly affect external validity: in a study area with more automobile-inclined residents than Seoul, compact land use may exert a stronger effect on automobile travel reductions and transit travel increases.