Regarding the first question (whether the typology should be theory driven or directed by blind empiricism), it is first necessary to evaluate the quality of theory. There are essentially five theories: (1) Homeless people belong to an underclass with a culture of its own that lacks the necessary personal structuring needed to develop a home life, employment etc, (Schiff, 1990). There is little, if any, evidence for this view. (2) Homeless people have “lost out in the battle for acceptance” and have gone through aversive learning experiences and as a result, they value their retirement from any institutional constraint (Levinson, 1963). This theory is compatible only with a very small fraction of homeless people, chiefly single men. (3) Homeless people have a faulty relationship with society, a “social disaffiliation” that may be brought about in various ways, for example, by mental illness, drug use, or other causes (Bahr and Caplow, 1970). This theory, which was popular for a while, fails to take into account the extensive social networks that recent empirical research has demonstrated for homeless people. (4) Homelessness as an extreme form of poverty resulting from the gap between income and available low-income housing. There is no single theoretical paper about this theory, but a lot of empirical evidence suggests an association between homelessness and severe poverty and unavailability of low income housing. (5) Societal disinvestment theory (Jahiel, 1992) accepts the premises of hypothesis but looks beyond it to decisions made by society to disinvest in certain geographic areas, types of work, or types of welfare support. It also fits the empirical evidence.
Based on this brief review, there seems to be little consensus around an explanatory theory, and virtually no theories specific to homeless families. Nevertheless, it would seem like theory may offer some guidance on the selection of candidate variables for further empirical exploration. For example, there is good support for theory 4 at the aggregate level (to account for the size of the homeless population). At the individual level, some vulnerability factors (ethnicity, pregnancy, substance abuse, past homeless history, various disabilities, physical abuse by spouse, and others as well as being in the wrong place at the wrong time) account for who is selected by society (societal disinvestment) or by self (societal disaffiliation) to become homeless.