Existing social theories explore the potential impacts of

Existing social theories explore the potential impacts of social capital on the health of older adults. Common models include social disorganisation dgat inhibitor (Browning, 2002) and collective efficacy models (Sampson, Raudenbush, & Earls, 1997). Although well developed and explored, these two models sometimes overlook the direct influence of physical environments on health, as well as the interaction of physical and social factors as etiological constructs. A modification of the specific ecological model proposed by Lawton (M. Lawton, 1980; M.P. Lawton, 1998) identifies the mechanisms by which \'neighbourhood\' impacts the health status of older adults through incorporation of both social and environmental factors. Originally, Lawton suggested that physical function and behaviours of an older adult are a function of balance between the demand of the environment (referred to as \'environmental press\') and the person\'s ability to deal with that demand (called \'competence\'). Small mismatches between these two factors will result in positive outcomes whereas large mismatches will result in negative outcomes and maladaptive behaviours (M.P. Lawton, 1998). For example, in a high risk crime environment, people who are psychologically and physically strong still go out and do their physical activity (a positive behaviour) whereas for people with lower levels of physical strength, the pressure of the environment may hinder positive behaviours (Glass & Balfour, 2003). We adapted Lawton\'s model to explain the potential combined impact of social and physical factors as \'environmental press\' for our outcome of interest, the occurrence of falls (Fig. 1). Features of social and built environments of a neighbourhood can act as the \'press\' for the occurrence of falls, and interact with individual factors to produce different numbers of falls. When individual factors overcome environmental pressures, there will be a low potential for falls. For example, a healthy individual can maintain a good level of balance on a slippery sidewalk and will not fall. When the force of the environment is very high, even in the presence of good physical health falls remain a possibility (top right side of the figure). In contrast, very frail older adults still are prone to falling even in a favourable environment. Every year, an estimated 30–40% of individuals in North America over the age of 65 fall at least once (Ambrose, Paul, & Hausdorff, 2013). The estimated annual prevalence of falls in community-dwelling Canadian seniors is between 20% and 30%, with a higher prevalence among seniors over 80 years (Canadian Community Health Survey – Healthy Aging (CCHS), 2010). About half of all falls occur outside the home in locations such as streets, parks, or shops (Lord, Sherrington, Menz, & Close, 2007). Falls among seniors result from a complex interaction between individual risk factors and contextual determinants. The role of individual and home level factors on the occurrence of falls is well-documented (Deandrea et al., 2010; Lord et al. 2007); however, conclusions from the few existing studies of the impact of neighbourhood built and social factors such as uneven sidewalks (Gallagher & Scott, 1997; Tinetti, Doucette, & Claus, 1995), social deprivation (Court-Brown, Aitken, Ralston, & McQueen, 2011; Syddall, Evandrou, Dennison, Cooper, & Sayer, 2012), the proportion of welfare recipients (Icks et al., 2009), and level of area wealth (West et al., 2004) are inconsistent. Methodologically, there exist two issues that are salient to the study of neighbourhood factors on fall-related health outcomes. The first issue is that the reliability and validity of measures of neighbourhood contexts that conceptually might be related to the occurrence of falls have seldom been investigated. The second is the issue of structural confounding, that is, the confounding resulting from social sorting mechanisms (Oakes, 2006). When examining social factors at the neighbourhood level, some subjects within certain strata of social variables because of social sorting mechanisms could never be exposed to the aggregate level exposures of interest. For example, in a classic US example, with the objective of studying the effects of racial segregation on preterm birth (Messer, Oakes, & Mason, 2010) very few black women lived in neighbourhoods with low levels of deprivation. That is, the subgroup of black women only experienced one level of exposure (high deprivation). This is referred to as ‘off-support’ (Ahern, Hubbard, & Galea, 2009) or ‘deterministic non-positivity’ (Diez Roux, 2004; Oakes, 2004) and when this happens, additional data collection will be of little assistance. Analyses of ‘off-support’ data in the presence of structural confounding rely on model extrapolations which do not permit examination of the independent influence of social factors, and thus limit meaningful causal inference in etiological analyses (Cole & Hernan, 2008). Despite growing awareness of this methodological issue, it has been quantified only in a few studies (Messer et al., 2010; Vafaei, Pickett, & Alvarado, 2014) and to our knowledge no such study has been conducted in social epidemiological studies of neighbourhood determinants of health in older adult populations. The objectives of our current study were therefore: (1) to develop a reliable and valid composite scale for measurement of neighbourhood-level social capital as perceived by older adults and to evaluate its psychometric and ecometric properties; (2) to examine the roles of neighbourhood-level socioeconomic status, social capital, and built environment factors as potential structural confounding variables in studies of the etiology of the occurrence of falls among older people.