This study adds to the nascent literature that seeks to identify how environmental factors, particularly alcohol outlet density, contribute to risk for IPV. Previous ecological analyses have used police-reported IPV events as the outcome (e.g., Cunradi et al., 2011
; Livingston, 2010
; Livingston, 2011
); this is the first study to make use of hospital records to explore the association between alcohol outlet density and IPV-related ED visits. Since, by definition, all cases in the analysis consisted of those who sustained IPV-related injuries requiring medical attention, it is reasonable to assume that our outcome measure represents a greater level of severity than police-reported IPV cases (although some of those cases also involve injury). With this in mind, our results can be compared to other ecological and multilevel studies on alcohol outlet density and IPV.
Our findings indicate that density of bars or pubs are positively associated with IPV-related ED visits throughout California over a 3.5 year period (2005–2008), even after accounting for Census-based neighborhood characteristics that have been shown to be related to health disparities (Berke et al., 2010
) and IPV (Cunradi, 2010
). In a multilevel study of IPV, McKinney et al. (McKinney et al., 2009
) found that on-premise alcohol outlet density was significantly associated with male-to-female partner violence (but not with female-to-male partner violence) among a national sample of married/cohabiting couples. Their measure of on-premise alcohol outlets, however, included both bars and restaurants where alcohol is consumed. It should also be noted that most of the IPV reported by couples in their sample consisted of ‘moderate’ aggression (e.g., pushing, shoving, grabbing), and not severe IPV, which is more likely to result in injury (Cunradi et al., 2002
). A cross-sectional ecological analysis by Livingston (Livingston, 2010
) found that general license density (either on- or off-premise consumption; mostly pubs and taverns) was significantly associated with police-reported IPV in Melbourne, Australia; on-premise density (mostly restaurants and small bars) were negatively associated with the outcome. In contrast, based on a longitudinal analysis using ecological data from Melbourne from 1996 to 2005, Livingston (Livingston, 2011
) found that neither general license density nor on-premise density were associated with police-reported IPV. Instead, packaged license density (mostly retail liquor stores) was positively related to the outcome. Finally, Cunradi et al. (Cunradi et al., 2011
), based on longitudinal analysis of ecological data from Sacramento, California, reported that off-premise outlet density, but not bar or restaurant density, was significantly linked to both IPV-related police calls and IPV-related crime reports.
The absence of individual-level data in this study preclude us from determining the precise mechanisms that link an increase of one bar per square mile with a 3% increased likelihood of IPV-related ED visits in a given zip code. It is possible, for example, that men who drink in bars that have physical or social characteristics that make violence more likely (e.g., Quigley et al., 2003
) may return home to their spouse/partner in a disinhibited, aggressive state in which conflict can rapidly escalate to IPV. Treno et al. (Treno et al., 2007a
), in a multilevel study of bars, hostility and aggression found that bars may serve to concentrate aggressive people into selected environments, and that these environments may serve to increase levels of aggression. Individuals with increased levels of hostility and alcohol aggression are more likely to choose bars as a venue for drinking (Treno et al., 2007a
). Similarly, women who are frequent bar goers may be more likely to drink heavily and use illicit drugs (Parks, 2000
; Parks et al., 2009
), placing them at increased risk for interpersonal aggression and victimization. The absence of individual-level characteristics in this study does not allow us to explore these hypotheses. Clearly, additional, multilevel research is needed to further investigate the mechanisms that underlie the association between bar density and IPV-related ED visits.
Our results indicate a small negative association between off-premise alcohol outlets and IPV-related ED visits, with an additional outlet per square mile reducing risks by 1%. This finding is not consistent with prior research, and should therefore be seen as preliminary. An alternative explanation is that alcohol obtained from off-premise outlets is probably consumed at home, and therefore less likely to result in physical aggression than alcohol consumed in the bar environment. Findings reported by Nyaronga et al. (Nyaronga et al., 2009
) on drinking context and drinking problems appear consistent with this explanation. For example, male and female survey respondents who were primarily bar drinkers were at increased risk for arguments and fighting; those who were primarily home drinkers were not at elevated risk. Moreover, Hispanic men and women and white men categorized as primarily bar drinkers were at increased risk for reporting problems with their spouse because of drinking; none of the primarily home drinkers were at increased risk in the adjusted models. The contribution of additional (unmeasured) socioeconomic or demographic factors in relation to off-premise outlets and IPV-related ED visits needs to be evaluated in future analyses. Our results showing that restaurant density is not associated with IPV-related ED visits is consistent with findings from other studies on alcohol outlet density and assaultive violence (Gruenewald et al., 2006
; Lipton and Gruenewald, 2002
This paper has a number of strengths and limitations. Regarding the latter, the correlations of exogenous variables are a potential limitation of the analysis. A potential concern is the extent that ED staff utilizes the appropriate E-code to identify IPV-related cases (Weiss et al., 2004
). The state of California mandates E-coding for ED injury cases (those with N-codes above 800), making California’s coding among the best in the nation (Annest et al., 2008
). At least one validity study for California ED data has been conducted (Goldman et al., 2011
), although it was not focused on IPV-related cases. Any bias introduced here, however, is unrelated to alcohol availability, thus mitigating this concern.
In terms of strengths, this study used a spatial misalignment variant of the standard Bayesian spatial modeling approach that allows the use of zip code data for longitudinal analysis despite frequent changes in these geographic units. The results indicate strongly positive spatial autocorrelation in the errors, suggesting the possibility of serious bias in analyses that do not account for spatially structured errors. To our knowledge, this is the first study to make use of these modeling techniques in order to explore the relationship of alcohol outlet density to IPV-related ED visits. This represents a new and innovative approach to gaining insight into how environmental factors contribute to risk for injurious IPV. While additional research is needed to further refine the findings reported here, these results add to a growing body of literature showing that alcohol outlet density is linked to many community problems, such as underage and young adult injures (Gruenewald et al., 2010
), alcohol-related car crashes (Treno et al., 2007b
), suicide (Johnson et al., 2009
) and child maltreatment (Freisthler et al., 2004
). From a environmental standpoint, policy changes that limit alcohol availability may be a critical step to help prevent many of these community problems (Livingston, 2011
; McKinney et al., 2009
; Zhu et al., 2004