Increasingly, policymakers have emphasized the value of research data on program efficacy as a necessary factor in the development of mental health services and systems of care. Evidence-based care is an approach to classifying research on service outcomes according to the amount and quality of evidence indicating that an intervention is effective (Sackett et al., 2000; Anthony, Rogers, & Farkas, 2004; Drake et al., 2003; Rog, 2004). Typically schemas for classifying evidence-based practices consider large, randomized clinical trials with adequate controls and unequivocal findings to be the highest standard of evidence required for an intervention to be considered evidence based. In fact, much of the recently published work on service innovation targeted at people who are homeless and severely mentally ill falls short of this standard, yet the relevance of the work is apparent in that it has emerged from practice experiences in response to sorely felt unmet needs.
Communities across the country have developed, implemented, and refined a wide range of program models and strategies to address chronic homelessness. Some of these models have been rigorously evaluated and others have been evaluated using less sophisticated methodologies. Some interventions have been implemented widely but little research exists to measure their effectiveness. New services for this population developed over the past decade include adaptations or modifications of established evidence-based interventions that were initially designed and tested for stably housed people with serious mental illness (Burns & Santos, 1995; Hwang et al., 2005), while other program innovations have shown promise based on non-experimental evaluations and have yet to be tested experimentally. Smaller studies of less rigorous design (e.g., comparisons of pre- and post-enrollment data for participants with no control group) and multiple case studies with reported outcomes, consensus of expert clinicians, and unpublished program evaluations, particularly when these sources produce a consistent pattern of findings, may also be considered as additional evidence to determine whether an intervention is considered evidence based (Rog, 2004). Accordingly, this paper will focus on a wide range of studies with relevance to the chronically homeless population, including studies with less rigorous methodologies and practice-based evidence emerging from the experience of providers and practitioners.