Without research that is aimed at constructing and refining models, the literature must remain a shapeless morass of almost random bivariate relations. Few authors have tried to construct theories or models in this area, although a few models of housing in general have been proposed (e.g., Rohe, 1985-86). Without theories, models, moderators or even many studies, meta-analyses are impossible, progress is impossible, and therefore understanding is impossible. Nevertheless, this review has attempted to round up what is known, and its tentative conclusions follow.