The phenomenon of homelessness is multidimensional with macro (health policy), meso (health care systems), and micro (individual) structural mechanisms. Homelessness is not a random event that occurs to families and individuals outside the context of their lives and personal history. Epidemiological medicine and social researchers continue to amass a body of literature whose focus is the identification and description of individual risk factors that are correlated with homelessness.

These studies have documented the rates of mental illness, substance abuse, experiences of childhood physical and sexual violence, and experiences of abuse and neglect (Bauman, 1993). This work has promoted the humanization of homeless people through its descriptive distinctions between the various subgroups within this population. However, focusing on individual-level risk factors, in describing who is at risk for becoming or remaining homeless is only part of the picture.

Contemporary analyses have looked at the interaction of individual and structural factors that contribute to homelessness. This approach continues to be informed by a simple, sequential causal relationship. What needs to be considered at this point in time is a model that stresses the myriad ways in which factors on the macro, meso, and micro levels interact in the formation of various pathways into homelessness. Researchers have pointed out that structural factors are heightened when there are fewer housing subsidies and the gap between median rents and median income is relatively wide. These structural factors in conjunction with individual factors such as gender, race, history of childhood or adult abuse, substance abuse, and the level of social support, contribute to a complex interplay exerting a dominant effect on homelessness (Ringwalt, Greene, Robertson, & Mc-Pheetes, 1998).
The life of a homeless person holds more uncertainty than its poverty. Homeless people are marginalized within the marginalization of poverty (Hall, J. M., Stevens, & Meleis, 1994). There are more labels for homeless people than for segments of mainstream America. There is fringe homeless, long term homeless, temporary homeless, emergency homeless, visibly homeless, and invisibly homeless. Within all of these categories there are different groups of homeless: single women never married without children, single women who are pregnant and underage, divorced women with children, single unmarried women with children, single men, divorced men with children, divorced men without children, families with children, runaways (minor children), adolescents, throw aways (children whose parents have told them to leave home and never return), lesbian and gay youth, transgender youth and adults, elderly, disabled, handicapped, veterans homeless, impoverished, immigrants, and illegal aliens. In addition to the aforementioned categories, there are homeless who have been evicted or those who are addicted to substances; there are homeless who are mentally ill; those who are homeless because of domestic violence and/or abusive family situations; and those who are homeless because of release from incarceration without transitional support mechanisms in place.
When considering all of the above categories of homelessness, how then does a generally accepted definition of “homeless” result? The National Coalition for the Homeless (2002) reports a definition according to the Stewart B. McKinney Act
...a person is considered homeless who “lacks a fixed, regular, and adequate night time residence, and has a primary nighttime residency that is: (a) a supervised publicly or privately operated shelter designed to provide temporary living accommodations...(b) an institution that provides a temporary residence for individuals intended to be institutionalized, or (c) a public or private place not designed for, or ordinarily used as, a regular sleeping accommodation for human beings.” 42 U.S.C. § 11302(a) The term “homeless individual’ does not include any individual imprisoned or otherwise detained pursuant to an Act of Congress or a state law.” 42 U.S.C. § 11302(c).
People experiencing homelessness in rural areas are less likely to live on the street or in shelters, and more likely to be “couch surfing,” living with relatives or friends in overcrowded or substandard housing. Although homeless people are heterogeneous, while experiencing homelessness they do have certain shared basic biopsychosocial needs, such as affordable housing, adequate incomes, mental and physical health care, and possible substance abuse treatment. All of these needs must be met to prevent and end homelessness.
An ongoing dilemma is estimating how many people are homeless. There are several national estimates, many of which are based on dated information. No one estimate is a definitive representation of an accurate count but only the best approximation. In 2000, the Urban Institute found that there were approximately 3.5 million people, 1.35 million of them children, who probably have or will experience homelessness in any given year (O’Sullivan, 2003).
Baumann (1993) reported that the research on homelessness could be divided into three levels of analysis. The first focus was on the individual with numerous biopsychosocial issues, disaffiliated, disabled, mentally ill and addicted, and living in a shelter. The second level focused on homelessness in the context of the person’s environment and the third level of inquiry defined homelessness as economic dislocation related to housing shortages. A significant amount of research focused on specific homeless population ssuch as those with mental illnesses and disaffiliated by society (McCarthy, D., Argeriou, Huebner, & Lubran, 1991).
Within the rise of the trajectory into homelessness there is a rapidly growing increase in the number of homeless elders. This can be attributed to their vulnerability to poverty and undertreated mental illness, accelerating a course of nursing home placement and/or early death. Women have become a major segment of the homeless population, with access to health care a major issue. Lim and colleagues (2001) conducted a study interviewing 974 homeless women in 78 homeless shelters and soup lines in Los Angeles County. Using multivariate analyses, the key enabling factors associated with improved health care access were having health insurance and a regular source of health care.
Families are the fastest-growing segment of the homeless population representing diverse backgrounds. Most are female-headed single-parent households with mounting incidences of violence, abuse, and neglect. Numerous researchers reported the intense stress and adverse effects that homelessness has on a child’s development, health, behavior, and academic success.
Research pertaining to homeless adolescents incorporated biopsychosocial, cultural, and spiritual health problems in addition to the homeless adolescent’s propensity for engaging in delinquent or maladaptive social and health behaviors. Concepts such as risk, resiliency, and connectedness were found to be critical for survival, supported by the creation of peer communities or street families (Ensign & Gittelsohn, 1998; Jezewski, 1995; O’Sullivan, 2003; Rew, Taylor-Seehafter,
Thomas, & Yockey, 2001).

Nursing research, education, and practice have philosophical foundations in advocating and facilitating health care for marginalized and vulnerable populations. In light of the increasing number of groups of homeless people and the known biopsychosocial outcomes of homelessness, intervention research is needed not only to prevent the trajectory of homelessness but also to develop programs and educate health care providers to the specific concerns of the homeless. Nursing research and advocacy as a course of action is essential on the macro, meso, and micro levels.