Fitzpatrick-Lewis et al. BMC Public Health 2011, 11:638 http://www.biomedcentral.com/1471-2458/11/638 one study from the current review reported that indivi- dual counselling was associated with reduced substance abuse and the number of risk behaviours [97]. Case management, when used consistently, appears to be a very effective intervention for homeless people with HIV. Case management has been found to improve mental health, use of health services, and improved overall health [99,101]. Moreover, the addition of hous- ing services is associated with improvement in housing status, with programs targeted for individuals with HIV/ AIDS being even more effective [99]. Implications for Research Of the studies identified as relevant for this review, study methodology was rated as moderate for only 10 of them, with the remaining rated to be of weak quality. Issues that resulted in studies being rated as methodolo- gically weak were generally related to either study design or statistical analyses. Researchers should be aware of these challenges so they can address or mitigate these limitations in future investigations. With respect to study design, it was difficult to ascer- tain the extent of selection bias, which would threaten the external validity of the results of many of the stu- dies. Selection bias may have arisen as a result of recruiting participants from a single program, shelter, or city. Moreover, some studies had such stringent inclu- sion criteria that those criteria themselves introduced the high potential for selection bias. Blinding of out- come assessors was also rarely addressed which intro- duces another potential source of bias. In terms of statistical analysis procedures, most studies lacked statistical power, as they did not have adequate sample sizes. As such, it was difficult to attribute a lack of between-group differences to the intervention not being effective and not simply a type II statistical error. Given the recruitment and follow-up challenges asso- ciated with individuals in this population, researchers can attempt to maximize statistical power by increasing actual effect size, decreasing sample variability, and increasing precision of outcome measurements. Many studies also failed to include basic statistical data such as effect size and lacked specific detail regarding out- come measures, thereby limiting the outcome analysis. Finally, the use of intention-to-treat analysis was rarely specified even in appropriate situations. Taking the unique methodological challenges asso- ciated with studying those who are homeless or at risk of homelessness into consideration, findings from stu- dies rated as methodologically weak were briefly pre- sented in this review where appropriate. Regardless of quality, these data contribute to the overall body of knowledge of how to best increase access to health, healthcare, and housing for those who are homeless or Page 10 of 14 at risk of homelessness. Moreover, the lack of new stu- dies of moderate or strong quality informs future research directions by identifying knowledge gaps. Addi- tional research is warranted examining homeless sub- groups of women, families, and children who have thus far been understudied. Furthermore, as homelessness is associated with a wide range of chronic disease such as HIV/AIDS, tuberculosis, schizophrenia, diabetes and hepatitis C [117-119], specific interventions targeting these conditions are needed. Study Limitations As a rapid review, this literature synthesis has a number of limitations. Some of these limitations are a product of the short timelines determined by the contracting agency to conduct the review. For example, grey litera- ture searching was limited in its scope, conference pro- ceedings and trial registers were excluded, and a limited number of relevant websites were selected for searching. In instances where data were unclear and/or incomplete, time constraints prohibited contacting authors to clarify data and citation tracking for subsequently published studies was not feasible. As a result of these limitations, it is possible that some potentially relevant studies were missed in the search. A further limitation of this review is that it synthesizes only methodologically moderate articles, as no methodologically strong studies were found and weak studies were not discussed in detail. Conclusions Health and social policies that include the provision of housing as an intervention can be effective for improv- ing health as well as housing status. Provision of hous- ing should optimally be provided within an integrated model in which other supportive services are offered on site. Such integrated models appear to be most effective in achieving and sustaining long-term housing, as well as increasing utilization of health care services for chronically ill homeless populations. These services can range from case management to the provision of meals. There is some evidence that a relatively simple interven- tion such as rental assistance increases time housed. For populations that are homeless or at risk of home- lessness that have substance abuse issues, housing that was contingent on abstinence had better outcomes than when no housing was provided on several outcomes including drug abstinence and maintaining stable hous- ing. While some benefit has been found related to absti- nence-contingent housing versus no housing, housing that is not contingent on abstinence was found to be most effective for improving long term housing tenure, substance abstinence, or psychiatric outcomes. Case management appears to be another effective intervention to improve health outcomes across various