Evaluating options for measurement of neighborhood socioeconomic context: Evidence from a myocardial infarction case–control study

Abstract

We hypothesized that neighborhood socioeconomic context would be most strongly associated with risk of myocardial infarction (MI) for smaller “neighborhood” definitions. We used data on 487 non-fatal, incident MI cases and 1873 controls from a case–control study in Washington State. Census data on income, home ownership, and education were used to estimate socioeconomic context across four neighborhood definitions: 1 km buffer, block group, census tract, and ZIP code. No neighborhood definition led to consistently stronger associations with MI. Although we confirmed the association between neighborhood socioeconomic measures and risk of MI, we did not find these associations sensitive to neighborhood definition.

Introduction

Socioeconomic disparities in health have received increasing attention by researchers (Adler and Ostrove, 1999) and policy makers (Mackenbach and Bakker, 2003) in recent decades. Socioeconomic status (SES) has been posited to be a “fundamental cause” of health disparities (Phelan et al., 2004; Williams and Collins, 2001), such that the association between SES and health is created when higher status individuals or groups mobilize flexible resources, such as money and prestige, to avoid illness and death. There is also evidence from human and animal studies that psychosocial stress in response to relative social status contributes to mortality and disease for low status individuals (Wilkinson, 1999; Steptoe and Marmot, 2002) and those living in more deprived areas (Elliott, 2000). Socioeconomic characteristics measured for individuals and areas have commonly included the domains of education, employment, occupational status, income, and material resources (Braveman et al., 2005; Krieger et al., 2002a; Carstairs, 2000). The questionnaires or other methods used to ascertain such characteristics differ across settings and studies (Krieger et al., 1997), and area-based socioeconomic characteristics have the additional complication of being measured at different scales or levels of aggregation (Pickett and Pearl, 2001).

In studies of neighborhood socioeconomic context and health, several scales of measurement are used without consensus as to which is most relevant. The modifiable areal unit problem, like the ecological fallacy, is a concern for such studies because study results may be sensitive to the selected measurement scale (Guagliardo, 2004; Dungan et al., 2002; Haynes et al., 2007). A geographic definition of neighborhood that is too vast might mask relevant variation and be subject to large-scale residual confounding. On the other hand, a restrictive geographic definition could exclude from consideration hazards and resources in the broader environment that affect health and behavior. The hypothesized mediators of the association between neighborhood context and health may dictate which geographic scale is most relevant (Diez Roux, 2003). For example, social interactions may be supported by the characteristics of a small area, such as one's block, whereas restaurants and stores across a larger area may provide access to healthy foods. Measuring the effect of socioeconomic context on health at different scales in a single study may help researchers to establish the plausibility of proposed mediators, interpret studies testing similar hypotheses at different scales, and engage in informed discussion about the utility of convenient neighborhood definitions.

Neighborhood socioeconomic context has commonly been measured for existing administrative areas (van Lenthe et al., 2005; Haynes et al., 2007), such as census or enumeration districts and postal codes; such administrative areas have different sizes in each country, and often have considerable variation in size by region within a single country. In the United States, neighborhood socioeconomic characteristics have most commonly been measured for census block groups or census tracts (Krieger et al., 1997), but United States Postal Service ZIP codes have been used as well (Davey Smith et al., 1996; Mobley et al., 2004; Philbin et al., 2000). Census block groups in the US contain approximately 1000 residents, census tracts 4000 residents, and ZIP codes 30,000 residents (Krieger et al., 2002a). A comparison to administrative units used in other countries may be useful, even though the correspondence is not exact: US census block groups are larger than very small units such as Canadian dissemination areas, British enumeration districts, or Australian collector's districts; US census tracts correspond approximately to medium sized areas such as Canadian census tracts, British election wards and postcode sectors, or Dutch postcode sectors; and US ZIP codes correspond to larger areas such as Canadian census sub-divisions or Swedish parishes (Schuurman et al., 2007; Carstairs, 2000; Brameld and Holman, 2005; Pickett and Pearl, 2001; Reijneveld et al., 2000; Kolegard Stjarne et al., 2002; Stjarne et al., 2006). Alternatively, the area within a specified distance of each address has also been used as a neighborhood definition, especially in studies of specific health-related behaviors such as physical activity (Duncan and Mummery, 2005; Frank et al., 2005) or smoking (Chuang et al., 2005).

Despite variation in the measurement of socioeconomic characteristics across studies (Braveman et al., 2005), SES has a well-documented relationship with health (Adler and Ostrove, 1999; Macintyre, 1997; Feinstein, 1993) and cardiovascular health in particular (Kaplan and Keil, 1993; Mensah, 2005; Davey Smith et al., 1998). An effect of neighborhood socioeconomic characteristics on cardiovascular disease risk has been documented even after adjusting for individual socioeconomic characteristics (Geronimus et al., 1996; Davey Smith et al., 1998; Sundquist et al., 1999; Diez Roux et al., 2001b; Steenland et al., 2004; Horne et al., 2004; Cubbin and Winkleby, 2005; Stjarne et al., 2006).

In this analysis, we investigated the strength of the neighborhood SES—incident myocardial infarction (MI) association across selected socioeconomic characteristics and neighborhood definitions. Five neighborhood socioeconomic characteristics were investigated: median household income (MHI), percentage below poverty level, percentage home ownership, percentage with a high school degree, and percentage with a college degree. Each of these measures was estimated for 1 km radial buffers, census block groups, census tracts, and ZIP codes. We hypothesized that the strength of the neighborhood context association with risk of MI would differ among the four neighborhood definitions considered. We hypothesized that socioeconomic characteristic associations with risk of MI would be stronger for relatively restrictive neighborhood definitions (e.g. block group), compared with larger geographic definitions of neighborhood (e.g. ZIP code). A relationship between neighborhood size and contextual association strength could be due to individual socioeconomic effects captured more accurately with a local contextual effect; alternatively one's immediate surroundings may have a particularly strong effect on stress, social support, health-related behaviors, and exposure to hazards independent of individual SES. We examined associations between measures of neighborhood context at different scales before and after accounting for the participants’ education, employment, and household income.