Abstract
Purpose:
As public housing agencies and other low-income housing providers adopt smoke-free policies, data are needed to inform implementation approaches that support compliance.
Design:
Focused ethnography used including qualitative interviews with staff, focus groups with residents, and property observations.
Setting:
Four low-income housing properties in Massachusetts, 12 months postpolicy adoption.
Participants:
Individual interviews (n = 17) with property staff (managers, resident service coordinators, maintenance, security, and administrators) and focus groups with resident smokers (n = 28) and nonsmokers (n = 47).
Measures:
Informed by the social–ecological model: intrapersonal, interpersonal, organizational, and community factors relating to compliance were assessed.
Analysis:
Utilized MAXQDA in a theory-driven immersion/crystallization analytic process with cycles of raw data examination and pattern identification until no new themes emerged.
Results:
Self-reported secondhand smoke exposure (SHSe) was reduced but not eliminated. Challenges included relying on ambivalent maintenance staff and residents to report violations, staff serving as both enforcers and smoking cessation counsellors, and inability to enforce on nights and weekends. Erroneous knowledge of the policy, perception that SHSe is not harmful to neighbors, as well as believing that smokers were losing their autonomy and being unfairly singled out when other resident violations were being unaddressed, hindered policy acceptance among resident smokers. The greatest challenge to compliance was the lack of allowable outdoor smoking areas that may have reduced the burden of the policy on smokers.
Conclusion:
Smoke-free policy implementation to support compliance could be enhanced with information about SHSe for smokers and nonsmokers, cessation support from external community partners, discussion forums for maintenance staff, resident inclusion in decision-making, and framing the policy as part of a broader wellness initiative.
Keywords
Purpose
The US Surgeon General has determined that there is no risk-free level of secondhand smoke exposure (SHSe). 1,2 Residence in multiunit housing is a significant risk factor for SHSe; smoke travels in common areas and through vents exposing both smokers and nonsmokers alike. 3 This exposure is particularly concerning for the individuals living in government-subsidized multiunit housing who are already at heightened risk of poor health because they are low-income, children, racial/ethnic minorities, and older adults.
The US Department of Housing and Urban Development (HUD) issued a rule in December 2016 requiring all public housing authorities to implement a smoke-free policy. Public housing authorities have 18 months to phase in the rule that will prohibit smoking in apartments, common areas, administrative buildings, and within a 25-foot perimeter around all buildings. 4 The rule could potentially impact nearly 1.1 million households. 5 In addition, HUD has encouraged managers of other HUD-assisted housing, specifically The Housing Choice Voucher Program (serving 2.1 million households) and project-based rental assistance (serving 1.3 million households), to adopt smoke-free policies. 4 It is estimated that between 9% and 19% of private residential management companies currently have smoke-free building policies. 6
Research to date has focused less on the implementation of smoke-free policies than on residents’ and multiunit property managers’ perceptions about motivations and barriers for choosing to adopt a smoke-free policy. Most residents support a property-wide policy, 3,7 -9 with nonsmokers, those with children, minorities, and those with an existing elective home smoking ban most supportive of the policy. 10 -12 Previous research also suggests that multiunit housing owners and directors see the benefits of a smoke-free policy such as decreased maintenance, fire and insurance costs, reduced resident turnover, ability to attract more nonsmokers, fewer resident conflicts, and better resident health. 13 -15 Although this body of research is instructive about attitudes toward adopting a policy, there is a lack of evidence to inform the strategies for planning and implementing the policy. One recent study examined public housing residents’ reactions to a newly implemented smoke-free policy finding that smokers and nonsmokers alike lacked understanding of the negative health consequences of SHSe, felt the policy was an infringement of their rights, and that interpersonal relationships were strained because of policy enforcement. 16
The expressed goal of eliminating SHSe requires residents to comply with the policy, which will likely require a change in their behaviors. Housing and Urban Development provided guidance on policy implementation for housing directors/managers including communication about the dangers of SHSe, provision of smoking cessation counseling, or alternatives to smoking (eg, e-cigarettes, nicotine patches, designated smoking areas), clear enforcement processes, and resident input into implementation 17 ; however, there is little known about how such guidance is used to inform implementation approaches and the context-specific factors that affect compliance.
To address this gap, we studied the implementation of a smoke-free policy ahead of the HUD rule in project-based rental assistance properties in the State of Massachusetts. We examined factors likely to influence compliance with the goal of informing future implementation efforts of housing managers and their public health partners as the rule is implemented nationwide.
Methods
Design
We used focused ethnography to conduct interviews with staff, focus groups with residents, and property observations.
18
This design allowed us to study the complexities surrounding a distinct issue in specific settings,
19,20
namely the smoke-free policy from resident and staff perspectives in low-income housing. Our study design, data collection measures, and analysis were informed by the social–ecological model in order to broadly contextualize implementation efforts and the factors that influenced resident compliance.
21,22
Specifically, we examined: Interpersonal/intrapersonal factors: physical environment (ie, common spaces, size, proximity to public/city space, Hallway use); social and historical environment (ie, wider social norms, historical context of property, other policies, perceptions of physical and social environment). Organizational factors: Supportive services/resources onsite, how policy is enforced, cessation support, methods for engaging residents, head office support and guidance, and resident beliefs about implementation and enforcement. Community factors: Resident attitudes, values, and smoking norms; social interactions and dynamics; individual behaviors; staff roles, leadership; attitudes values; and smoking norms of property manager and staff.
Setting
In August 2015, a private residential management company that provides HUD-assisted housing adopted a 100% smoke-free policy across its 52 properties in 6 Eastern states. The company’s smoke-free policy states that smoking, including e-cigarettes and smokeless tobacco, is not permitted anywhere on any of the properties, including apartments, common areas, parking lots, landscaped areas, or at any corporate office. The implementation plan included a 1-year preadoption planning process with multiple resident meetings, a video made and distributed to residents about the benefits of going smoke-free, and monthly reminders about the policy and cessation support opportunities, required lease addendums, enforcement process with 3 lease violations and then pursuance of eviction, training for all levels of staff, and certification of resident service coordinators (RSE; those responsible for providing support to residents and issuing lease violations) as American Lung Association group cessation counselors, and ongoing offering of 8-week cessation classes. This company independently chose these planning activities prior to contacting our study team for comment on an educational video they had developed in support of their smoke-free efforts. After this initial contact, we developed our relationship further by seeking external funds to assess the processes and outcomes of their smoke-free efforts. Our study team did not contribute to program development or implementation. Staff and resident perceptions of the implementation of this plan is the focus of this study.
To examine the experiences at the property level and limit the differences in state and corporate contexts, we focused our study on properties in Massachusetts. Eligibility criteria of housing properties included having at least 150 apartments, an RSC, being a HUD Project-Based Section 8 Rental Assistance property serving extremely low-, low-, and very low-income households, 23 and offering housing to families (rather than only seniors). These criteria were chosen because properties with RSCs offered onsite cessation support, and family housing provided an opportunity to explore whether having children in the house may influence attitudes and behaviors. From the eligible list of 8 properties, we utilized a maximum variation purposive sampling approach 24 to ensure the selection of a diversity of geographic locations (large urban centers in the East and West of the State, smaller communities in the center and Southeast part of the State), and housing type (garden, mid-rise, high-rise). The properties varied by number of units, ranging from 967 garden/townhouse units in a sprawling urban campus, to 190 mid-rise units in a small, suburban community (Table 1). They also varied in racial/ethnic composition and proportion that were elderly patients and/or disabled (eg, percentage of black ranged from 14% to 54%; Hispanic ranged from 14% to 56%; elderly patients/disabled ranged from 18% to 68%).
Site Description.
a To maintain anonymity, city names are not listed here.
Within each of the initial 4 properties chosen, we used purposive-stratified sampling 24 to identify focus group participants based on smoking status. Our rationale was that previous studies suggest there are different responses to the policy by smoking status. The study reached saturation after 4 properties, as no new information or themes were being generated.
Participants
Seventeen individual interviews with property staff were held: 4 property managers, 4 RSCs, 4 maintenance managers, 3 patrol officers, and 2 “other” administrative staff who self-identified as smokers and wanted their perspective to be heard. These categories of staff were chosen because each had a unique perspective and role that, when analyzed together, offered a more comprehensive understanding of the environment they collectively created at each property site. Our selection of staff categories for inclusion in interviews was informed by initial conversations with the corporate staff. Through their own planning processes, they identified that each of these types of staff would likely play an important role in enforcement. Residents were recruited to the focus groups through fliers, announcements in a monthly written newsletter and at property events, and by word of mouth. At 3 of the properties, 2 focus groups were held, 1 with smokers, and another with nonsmokers. At the fourth property, 1 group with smokers and 2 with nonsmokers were held because after the first group, there were additional nonsmokers who wanted to participate. In total, across the properties, 28 smokers and 47 nonsmokers participated in the groups.
Data Collection
Data collection took place during September to November 2016, purposely, 1 year after the adoption of the policy, and was performed by the first and fourth authors. Each site visit lasted 1 to 1.5 days. Data collection strategies included property observations, semistructured interviews, and resident focus groups, with the goal of enhancing and explicating findings from any single source. 25,26
Observation forms guided collection of information on the physical environment, including the size of the property, upkeep, type of housing, playgrounds, and how such spaces were used, evidence of smoking, and the proximity to city streets was documented.
The use of semistructured interviews with program staff allowed for obtaining detailed opinions and assuring confidentiality when discussing the policy. Interviews lasted approximately 60 minutes and were held in a private room on the property.
Focus groups provided information on residents’ perceptions about the smoke-free policy and possible messages and cessation support. The focus groups were uniquely suited for understanding the social dynamics in the face of this policy change. 26 Focus groups lasted approximately 90 minutes and were held in a private room on the property. Interviews and focus groups were audio recorded and transcribed verbatim to facilitate joint analysis by the research group. Individuals were provided with a written statement about the research. A gift card of $25 was provided upon completion of the focus group for each participant. A waiver of documentation of consent was granted from the institutional review board of Harvard TH Chan School of Public Health.
Data Analysis
A theory-driven immersion/crystallization analytic process 27 was used to cycle through stages of examining portions of the raw data in great detail and then identify patterns and themes, framed by the social–ecological model. Specifically, 2 members of our study team examined each transcript with MAXQDA (version 12.2.1) 28 qualitative data management software and coded the broad social–ecological model categories of intrapersonal/interpersonal, organizational, and community factors and some other high-level codes within these categories, such as “knowledge,” “beliefs/opinions,” “behaviors.” During this process, they also kept a running memo for ideas about each separate transcript. Code reports were then shared with a 4-member research team. Each member of this team was responsible for summarizing and understanding 1 specific site. They developed an MS Excel file where they identified and sorted themes with thoughts and illustrative quotes, allowing for patterns to emerge. These themes were then discussed with the wider research team on 2 levels: (1) across respondent type to determine whether there were themes common across sites for all managers, RSCs, residents, and so on and (2) site specific, assessing the environment in which the policy was being implemented. As part of these discussions, we included an open reflection of our beliefs and biases to seek out and consider alternate explanations and themes. The broader team meetings then motivated the data analysts to rereview the transcripts to examine other ideas and themes. This iterative process was considered complete when no new themes were generated from transcript review and discussion.
Results
Self-reported compliance and the most salient factors influencing compliance by social-ecological level were identified across respondent type and site. Illustrative quotes by respondent type are listed in Table 2.
Illustrative Quotes by Topic and Participant Type.
Participant Characteristics
A majority of the participants were female (67%) and without children <18 years old living in their home (76%). Just over half of participants categorized their race as white (56%), 25% as black, and 19% as mixed race or other. More than half of the participants either had a high school degree/General Equivalency Diploma (GED) (33%) or did not complete high school (19%). The average age was 54 (range: 20-86), and the number of years living in the community was 12 (range: 0-61). None of the participant characteristics differed significantly by smoking status (Table 3).
Resident Participant Characteristics by Housing Site.
Abbreviations: GED, General Equivalency Diploma.
Intrapersonal: Compliance With Policy
All categories of respondents—resident smokers, resident nonsmokers, and staff—reported a reduction in smoking and SHSe. When the policy was first adopted, there were frequent reports of smoking incursions by neighbors and staff reports of witnessing smoking on the property. However, as smokers realized the potential for eviction, by seeing others get a lease violation, hearing rumors, or receiving one themselves, they increasingly complied with the policy.
Nevertheless, the overall reduction in SHS does not imply a 100% smoke-free campus. Most smokers reported leaving the property when convenient and adapting their behavior in order not to get caught. They waited until nights and weekends to smoke on property with fewer staff to report a smoking violation, or they devised methods for “hiding” their smoke by sitting near vents (typically in their bathroom) or using air filters within their apartments. Many smokers who used to smoke outside in courtyards or balconies, often in the company of friends, had now gone indoors.
Intrapersonal and Interpersonal: Beliefs
Nonsmokers and staff felt that the smoke-free policy had a direct and substantive effect on their rights. They spoke about their own health and vulnerability and that the policy provided a means to advocate for their own health. Although nonsmokers felt that the policy increased their sense of agency, the smokers felt a loss of autonomy, human dignity, and a lingering questioning of why they were being singled out when mental health, substance abuse, and violence issues exist in the community.
In addition, before the policy was adopted, there were some residents who only smoked outside —typically because they did not want the smoke to linger in their apartments or affect their children. However, the vast majority of smokers interviewed lived without children (∼78%), with other smokers, or alone and did not readily mention the potential impact their smoking was having on others. After probing by the interviewer, some would acknowledge that exposure to tobacco smoke was dangerous for nonsmokers in their units, but they did not seem convinced that someone in another apartment could be exposed to their smoke.
Organizational: Enforcement
We asked residents and staff their opinions about enforcement practices. Without fail, staff at the properties felt that the head office created a detailed and well-thought out plan for enforcing the policy. Staff praised the clear guidelines for addressing violations and possible evictions. They also praised the year-long preadoption planning period where each property held numerous meetings with residents, made addendums to leases, and offered cessation classes. Staff, such as the residents themselves, reported that residents understood the potential for eviction and this was a primary motivator in compliance. Staff reported various discussions with residents where they reiterated their commitment to enforcement and that they had the will and the mechanisms in place to pursue an eviction if it came to that.
However, despite the long planning period, clear policy, and messaging, there remained numerous challenges to addressing smoking violations. For one, the role of maintenance and grounds staff changed significantly. They typically had the most day-to-day interaction with residents because they walked the grounds, attended to maintenance requests in resident apartments, and performed regular apartment inspections. They were the “eyes and ears” of property management and were relied on to report smoking violations. Most maintenance staff were ambivalent about this role, feeling concerned about a deterioration in trust between themselves and residents or fearing retaliation. Therefore, there seemed to be an ad hoc system in place where maintenance staff would witness a smoking violation and then wait to report it so the lease violation would not be tracked back to them.
In addition to maintenance staff’s role in enforcement, nonsmoking residents’ role in enforcement was complicated and many expressed ambivalence about reporting their neighbors. Although they wanted a smoke-free home, they did not want to compromise their relationships with their smoking neighbors, and some expressed fear of retaliation as well. On the other hand, the smokers who abided by the rule felt emboldened to hold others accountable as well.
Both smokers and nonsmokers reported a hazy understanding of how the policy was being enforced by the management. There were rumors of violations and evictions, but in general, unless a resident was individually affected, they were unsure of management’s actions. This lack of knowledge led some residents to believe that “nothing was happening.”
Organizational: Smoking Cessation and Support
Most resident smokers believed the unspoken requirement of the smoke-free policy was for them to quit smoking. In part, this was because the policy forced them to change where they typically smoked, that is, in their home and immediate vicinity. In addition, management’s method to support adherence to the policy (other than enforcement via lease violations) was to offer smoking cessation guidance in their newsletters and through group classes.
Residents differed in their response to this perceived requirement to quit. Almost everyone interviewed was a long-time smoker with multiple quit attempts, yet some felt the policy provided a new motivation for them to quit, while others felt that the policy encouraged smoking, almost as an act of rebellion. Most people, however, fell somewhere in the middle; they did not believe they could quit but also wanted to comply with the policy.
Only 1 of the 4 properties had anyone participate in the smoking cessation group class offered by the property RSCs. At that site, some of the participants quit short term but resumed by the time of this data collection. The lack of participation in the classes was partly due to smokers’ beliefs that they would not be helpful since they had already “tried everything.” In addition, there was a perceived inherent issue with the class being offered by staff, playing both “good cop and bad cop.” Residents who were former smokers suggested they could play a supportive role and in 1 site nonsmokers participated in the group class so they could share what they learned with their neighbors.
Organizational: Resident and Staff Opinions
Smokers, nonsmokers, and many staff agreed that the campus-wide policy made compliance particularly difficult. Without fail, all smokers wanted a designated outside smoking area and the ability to smoke in one’s car on property. From their perspective, allowing for smoking on the property would help them not smoke inside, support their sense of autonomy and respect, and provide a safer environment than on a city sidewalk or park. In addition, both staff and residents described how large groups of people standing in front of the property smoking was unsightly and complaints from neighbors from properties nearby were common. Staff and nonsmokers also discussed the idea of having a designated outdoor smoking area. Although they believed it would reduce smoking indoors, they also wondered if it was feasible, with smoke streaming into nearby windows.
In addition to designated smoking areas, smokers also advocated for allowing e-cigarettes, feeling it would be an effective way to address their addiction while inside, as well as support for renovating their apartment. In 3 of the 4 properties, resident smokers described how difficult it was to comply with the policy when their apartment remained infused with tobacco odor, triggering their desire to smoke.
Community
Each of the properties had renovated, clean common spaces and landscaped grounds. Two of the properties had easy access to a city street, and observations were made of people smoking off-property. There was no immediate evidence of smoking on-property (no odor and no cigarettes butts) either during the day or in the early evening.
The residents responded to the smoke-free policy in the context of the broader historical and social environment. Two of the 4 properties were in transition from being a largely older, single-resident community to integrate younger families, many of whom had different cultures and languages. The third property was acquired from a largely absent management company that did not maintain the property and residents felt unsafe because rules were not enforced, so residents were surprised when policies by the new management company were consistently applied. How residents understood enforcement of the policy, who was being singled out, and the impact on the community was understood within these contexts.
Although these broader social and historical factors seemed to play a role in implementation of the policy, the differences in physical environment, that is, the size and type of property, did not seem to influence overall perceptions and adherence to the policy. Whether the smoker had to travel across a large property or take an elevator and cross the street, the same issues of inconvenience, concern for safety, infringement of rights, enforcement roles, and challenges with smoking cessation existed.
Discussion
This study examined multiple levels of social–ecological factors that influenced resident compliance. We found that opinions and behaviors of residents and staff were quite similar across properties despite differences in the physical and social environments. Participants reported that the smoke-free policy decreased, but did not eliminate, their exposure to SHS. Staff felt that strong and consistent enforcement of the policy was most important for compliance, yet challenges to this enforcement included inability to enforce on nights and weekends, relying on ambivalent maintenance staff and residents to report violations, and staff to be both enforcers of the policy and provide smoking cessation. In addition, resident smokers believed they were being told to quit smoking, which they felt to be a violation of their autonomy, while also not feeling convinced that their smoke harmed neighbors’ health. They also believed that smoking should not be singled out and enforced when many other issues on the property, often seen as more dangerous than smoking, were not being addressed. Yet, the single greatest challenge to compliance reported by smokers was the property-wide ban. Resident smokers wanted a smoking area on property and allowance of e-cigarettes. Otherwise, they felt that they would continue to find ways to “hide” their indoor smoking. Many staff and nonsmoking residents agreed that a smoking-designated outdoor area would help smokers comply with not smoking indoors.
These findings identify specific challenges that may need to be resolved to ensure effective implementation of smoke-free housing policies. At the individual/intrapersonal level, there should be an explicit recognition that this policy diverges from previous smoke-free policies in restaurants/public spaces because it requires individuals to change what they do in their homes. It confronts the meaning of “home” as it relates to residents’ personal agency and power, with conflicting outcomes for smokers and nonsmokers. Indeed, previous research found that the most persuasive messages to promote a smoke-free housing policy related to nonsmokers’ individual rights such as, “You have the right to breathe clean air in your home,” and the most persuasive messages against the smoke-free policy related to smokers’ rights such as, “People have the right to smoke in their own homes.”(P4)29 Possible strategies to address these challenges that have not been reported in previous literature could include clearer messages about how smoke travels through vent systems and the dangers of SHSe, ensuring the focus is on the smoke rather than the smoker, and tangible activities to involve nonsmokers in promoting (rather than only enforcing) the policy, for example, stories about their need for clean air, former smokers providing peer support, residents’ perceptions that their complaints about smoke incursions are taken seriously by management, and so on.
At the organizational level, there should be recognition that the smoke-free policy is typically implemented in low resource environments. Round-the-clock enforcement with overburdened staff who must also address other high-priority issues presents significant challenges. Potential strategies that rely less on enforcement could include partnerships with community organizations to provide individualized and confidential cessation support rather than having property staff be both counselors and enforcers, forums for maintenance staff to discuss concerns about their role in enforcement and identify solutions, and resident inclusion in decision-making about smoking areas and e-cigarettes.
At the community level, we found that the management company’s investment in an appealing physical environment and related community amenities were appreciated by residents, and in turn, residents took pride in their community. However, while this investment was valued, it was not sufficient in ensuring compliance to a smoke-free policy. Couching the policy as only one part of a broader health and wellness initiative that residents embrace may prove useful. Additionally, there was variability in the social milieu of the sites and how residents understood their community; however, the implications this had on the level of compliance is unclear. Further exploration around factors such as social cohesion is warranted in future studies. Taken together, our findings suggest that compliance with the smoke-free policy requires enforcement along with transparent communication, and opportunities for collective staff and resident input into policy implementation details.
Our study has certain limitations and strengths. We examined the smoke-free policy 1 year after its adoption. A study conducted over a longer time frame would be required to determine whether smokers’ behavior complies to the policy with more time and continued enforcement efforts. Similarly, a longer study would be required to determine whether SHSe would continue to decline or whether implementation efforts would lapse and smoking on properties would regress to prepolicy exposure levels. Because this study focused solely on the experience of one management company’s policy implementation at 1 point in time in 1 state, we cannot conclude with certainty whether a different planning and implementation process would promote better compliance. The management company also invested time and resources into this effort, which other housing companies and agencies may not be able to do, yet even with this level of investment, we found substantial implementation challenges. In addition, because our study gathered nuanced and in-depth data from multiple levels of staff, resident smokers, and nonsmokers, we were able to identify factors that are likely important in other settings, such as resident concern for losing their housing, staff’s inability to enforce outside of daytime weekday work hours, and desire for a designated smoking area. The nature of our qualitative study did not allow for stratification of findings by demographic characteristics. For example, our demographic forms were anonymous to protect residents’ concerns about confidentiality. We also did not enumerate behaviors during the focus groups (eg, a show of hands for changes in behavior) because (1) we did not want to stigmatize existing behaviors, and (2) the purpose was to examine the supports for compliance rather than assessing compliance per se. Nevertheless, future research should include a diversity of geographic sites, both public and private management companies, random selection of sites and residents, and further explication by subgroups.
In conclusion, this study fills a gap in the field’s understanding of smoke-free policy in low-income housing 6,30,31 by providing a novel exploration of the social–ecological factors that influence compliance, from the perspective of both staff and residents, and offering timely insights and practical recommendations including: consistent and clear enforcement, messages that reach smoking residents, resident engagement (eg, resident ambassadors and committees) for decision-making (eg, designated outdoor smoking, e-cigarettes), positive roles for non-smokers, transparent communication, forum for staff to discuss concerns, and individualized cessation support by community organizations. Additionally, there may be advantages in implementing the smoke-free policy as part of a broader community health and wellness effort.
So What? Implications for health promotion practitioners, low-income housing policy makers, and researchers:
What is already known?
The Department of Housing and Urban Development is requiring all public housing to go smoke-free. Although there is general support for this policy among public housing staff and nonsmoking residents, very little is known about promising practices to support compliance.
What does this article add?
This study represents a novel exploration of the social–ecological factors that influence compliance, from the perspective of both staff and residents, providing timely insights and recommendations for policy implementation.
What are the implications for policy makers, practitioners, and researchers?
New insights for policy implementation and research include consistent and clear enforcement, messages that reach smoking residents, resident engagement (eg, resident ambassadors and committees) for decision-making (eg, designated outdoor smoking, e-cigarettes), positive roles for nonsmokers, transparent communication, forum for staff to discuss concerns, and individualized cessation support by community organizations. The smoke-free policy should be part of a broader community health and wellness effort.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was supported by NIH grant number 3R25CA057711 & U.S. Department of Housing and Urban Development, Healthy Homes grant number MAHHU0025-14. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.
