Whatever the purpose of a typology, its development entails a series of decisions and choices that require comprehensive knowledge of the population, the research that produced the knowledge, and the tradeoffs with the available approaches to typology development. There are several gaps in the knowledge of the overall homeless family population that hinder the development of a typology that can provide the most coverage and be of maximum utility for practice and policy. One gap is the lack of research on homeless families across the country, especially studies involving midwestern or southern populations, as well as those in rural areas. Much of the current knowledge is based on research in specific cities, such as New York, Boston, Worcester, Massachusetts, and the cities involved in the multisite initiatives. This is a particularly important gap to fill given the role that context plays in affecting who becomes homeless, the course of homelessness, and the service response.
In addition to lacking geographic diversity, population coverage of most of the studies that have been conducted is limited. For example, few studies focus specifically on families at risk for homelessness or families before they become homeless. Most of the research attempts to collect data retrospectively on families before they became homeless and provides only a limited understanding of the possible factors that buffer other similar low-income families from experiencing homelessness.
Little is known about the families who fall back into homelessness after receiving interventions. Although subsidized housing is shown to assist 80 to 90 percent of families out of homelessness, 10 to 20 percent of the families continue to be residentially unstable in spite of the assistance. Understanding the extent to which the difficulties are contextually-based or involve other factors is critical to understanding this key subgroup, which may end up being one of the major purposes for a homeless family typology. Also, very little is known about the subset of families who are working but remain homeless. Understanding their needs and experiences while homeless and the factors that impede their residential stability would be useful in aptly characterizing these families.
When one talks about homeless families, one almost always refers to homeless mothers and their children. Most studies have omitted two-parent families and few have collected data on the men who once were, or who remain, part of these families. Similarly, some of these families are part of extended family networks that may be critical to both prevention and intervention efforts. In addition, although studies have noted that many single homeless adults are parents, few studies have examined their familial roles.
Because many studies of homelessness have been funded by agencies charged with understanding mental health and substance abuse, much of the literature focuses on people with these conditions. As Arrigo (1998) writes, there is no mention of "modest or moderate needs" homeless families. Although efforts to identify and understand families with the greatest needs make sense for agencies that want to intervene with those most in need, these studies may distort the understanding of the levels of need in the overall population.
Finally, few studies have had a longitudinal perspective that could provide insight into the trajectories families take into and out of homelessness. Little is known about families that become homeless only once or that are residentially unstable for long periods of time.