Estimates of MUH residency were determined by using national and state representative data from the 2009 American Community Survey (ACS), an annual household survey conducted by the U.S. Census Bureau. The sampling frame includes all valid residential addresses in the 50 states and DC. The ACS is primarily a mail-based survey; however, if no response is received, follow-up is attempted via computer-assisted telephone and in-person interviews. In 2009, 1,917,748 respondents were interviewed (one per household). The overall response rate was 98.0%; state-specific response rates ranged from 94.9% to 99.4% (U.S. Census Bureau, 2012).

Estimates of smoke-free home rule prevalence were obtained from the 2006–2007 Tobacco Use Supplement to the Current Population Survey (TUS-CPS), a cross-sectional household survey of adults conducted by the U.S. Census Bureau. Data were collected from approximately 240,000 respondents in May 2006, August 2006, and January 2007, with overall response rates ranging from 80.0% to 85.0% across the three data collection periods (National Cancer Institute, 2012).

For this analysis, a MUH resident was defined as any respondent who reported living in a “one-family house attached to one or more houses,” or a building with between “2” and “50 or more” apartments. Respondents were not considered MUH residents if they reported living in a “one-family house detached from any other house,” “a mobile home,” or “boat, RV, van, etc.” Sociodemographic characteristics included sex, age, race/ethnicity, and poverty status. Poverty status was defined by using 2009 U.S. Census Bureau thresholds. Respondents were classified as having a smoke-free home rule if they reported that smoking was prohibited inside their home.

For each state and the United States overall, the number of MUH residents with smoke-free home rules was determined by multiplying the prevalence of adults with self-reported smoke-free home rules (TUS-CPS) by the respective number of MUH residents (ACS).

The number of MUH residents who have experienced an SHS infiltration in the home was determined by multiplying the national and state-specific number of MUH residents with smoke-free home rules by a range of 44%–46.2%. This range was derived from all published peer-reviewed studies that have assessed self-reported, past year SHS infiltration among MUH residents with a smoke-free home rule, either during or after the period (2006–2009) when the TUS-CPS and ACS data were collected (King, Cummings, et al., 2010; Licht et al., 2012). To ensure comparability with ACS estimates, studies of specific MUH subpopulations (e.g., public housing) were not considered in the infiltration range.

In both of the studies that were used to determine the prescribed range, the extent of SHS infiltration was calculated among MUH residents with a smoke-free home rule. However, different questions were used to define SHS infiltration. In Licht et al. (2012), which was fielded in 2010, respondents were considered to have experienced SHS infiltration if they responded “most of the time,” “often,” “sometimes,” or “rarely” to the question, “In the past 12 months, how often has tobacco smoke entered your unit from somewhere else in or around your building?” In King, Travers, et al. (2010), which was fielded between 2007 and 2009, SHS infiltration was defined as a response of “daily,” “a few times a week,” “once a week,” “once every couple of weeks,” or “once a month or less” to the question, “During the last 12 months of living in your unit, how often has SHS entered into your living space from somewhere else in or around the building?”

The findings from this study reveal that over one-quarter of the U.S. population (79.2 million individuals) resides in MUH and that disparities in MUH residency exist across subpopulations. The findings also show that an estimated 27.6–28.9 million MUH residents with smoke-free home rules have potentially experienced an SHS infiltration in their living unit that originated from elsewhere in or around their building. Separating smokers from nonsmokers, cleaning the air, and ventilating buildings cannot eliminate exposure of nonsmokers to SHS. Therefore, policies prohibiting smoking in MUH, including living units and indoor shared areas, represent the most effective way to fully protect MUH residents from involuntary exposure to SHS in this environment.

Smoke-free MUH policies are favored by most MUH residents (Hennrikus et al., 2003; Hewett et al., 2007; King, Cummings, et al., 2010; Licht et al., 2012), are legally permissible in both government-subsidized and market-rate housing (Schoenmarklin, 2009), and can result in cost savings for MUH operators (Ong, Diamant, Zhou, Park, & Kaplan, 2012). Moreover, the U.S. Department of Housing and Urban Development (HUD) has encouraged public housing authorities, as well as owners and management agents of multifamily housing rental assistance programs, such as Section 8, to adopt and implement smoke-free policies for some or all of their properties (HUD, 2009, 2010). Nonetheless, few MUH operators have implemented smoke-free policies, and many have misconceptions about implementation barriers (Hewett et al., 2007; King, Cummings, Mahoney, & Hyland, 2011). Therefore, initiatives to reduce SHS in MUH should include efforts to educate MUH operators about the benefits of smoke-free policies.

To our knowledge, this study is the first to report national and state estimates of MUH residency and SHS infiltration among U.S. MUH residents. Nonetheless, the findings are subject to at least four limitations. First, MUH residency and smoke-free home rule prevalence were determined from data collected at different times. However, it is unlikely that any significant changes in these estimates occurred during the 2-year period between which the data were collected. Second, smoke-free home rule estimates were obtained from the general population and may not be generalizable to MUH residents. However, estimates of smoke-free home rule prevalence among MUH residents are comparable to those of the general population (King, Cummings, et al., 2010; Licht et al., 2012; National Cancer Institute, 2012). Third, the SHS infiltration range used in this study was based upon data collected across multiple years (2007–2010). Since research suggests that the prevalence of smoke-free MUH buildings has increased with time (King et al., 2011), the inclusion of older data could lead to overestimation of SHS infiltration. In order to account for potential declines in SHS infiltration over time, the present analysis included only national and state representative studies conducted during or after the time period in which the MUH residency (2009) and smoke-free home (2006–2007) data were collected. Finally, the SHS infiltration range was based upon two studies conducted nationally and in one state (New York), which may limit generalizability to other states and subpopulations. Accordingly, future research could include state-level studies to verify and expand upon the measures and findings presented in this study.