Homicides and socio-environmental determinants of health in Brazil : a systematic literature review

Brazil currently has the highest absolute number of homicides in the world, which results from a complex range of factors. This study aimed at understanding the associations between socio-environmental determinants of health (SDH) and homicides in Brazil through a systematic literature review. The review followed PRISMA guidelines, selecting quantitative and qualitative studies published in Portuguese, English, and Spanish carried out between 2002 and 2017, available in the PubMed, MEDLINE, LILACS, SciELO and BVS-BIREME databases. Two trilingual reviewers tracked studies independently by basing on the eligibility criteria. We critically assessed the selected studies with the Critical Appraisal Skills Programme (CASP) or the Checklist for Analytical Cross-Sectional Studies, depending on the study design. We considered 60 studies and grouped their SDH into categories to develop a narrative synthesis about each SDH. These categories were: territory; race/ethnicity; gender; age; social inequalities and economic factors; development; education; work and employment; drugs and trafficking; other SDH. We found some SDH were more associated with homicides, such as being young, black, male, of low education level, and also people who lived in places of high social inequality, such as urban suburbs and agricultural frontiers. Unemployment and drug trafficking, as well as intersections between various SDH were also prominent. Education seems to be a protective factor for homicide. Despite the limited capacity of interpretation due to the high range of methodological approaches, this review shows the importance of considering SDH and their intersections when developing homicide prevention policies. Homicide; Violence; Social Determinants of Health Correspondence C. Wanzinack Rua Jaguariaíva 512, Matinhos, PR 83260-000, Brasil. cloviswa@gmail.com 1 Universidade Federal do Paraná, Curitiba, Brasil. 2 Universidade Regional de Blumenau, Blumenau, Brasil. doi: 10.1590/0102-311X00012818 Cad. Saúde Pública 2018; 34(12):e00012818 REVISÃO REVIEW This article is published in Open Access under the Creative Commons Attribution license, which allows use, distribution, and reproduction in any medium, without restrictions, as long as the original work is correctly cited. Wanzinack C et al. 2 Cad. Saúde Pública 2018; 34(12):e00012818 Introduction According to the 49th World Health Assembly, held in 1996 1, violence is a public health issue that holds no consensus regarding the concepts, causes, and consequences of this complex subject. This study understood violence as a process of many historical causes that need to consider its cultural, economical, sociopolitical, environmental, and legal aspects in its analyses 2. Violence can manifest itself in different ways, including homicide, which is the pinnacle of violence, because it implies life annihilation. Homicides are the fourth main cause of death among people aged between 15 and 44 years old in the world 1. This study understood “homicide” based on the Brazilian Criminal Code, which defines it as the act of killing another person, be it due to malice, when there are intent and awareness of results, or due to guilt, negligence, or recklesness 3. Homicide is one of the most important violence indicators, and the one that most clearly depicts the magnitude and severity of the situation 2. Estimates show that in 2012 approximately 475,000 people were victims of homicides worldwide, a rate of 6.7 homicides per 100,000 inhabitants 1. The rate in the American continent is 28.5/100,000, followed by Africa, with 10.7/100,000 1. These rates did not evenly distribute homicides considering genders, age groups, and socioeconomic factors. Men represent 82% of the victims, with estimated rates 4 times higher than women 1. The highest rates of homicide worldwide are among men aged between 15 and 29 years old (18.2/100,000) 1. In Brazil, since the 1980s, there has been a significant growth in homicide-related deaths, particularly in urban environments, with young black males mostly being both aggressors and victims 4. Recent studies point out to social inequalities as one of its main determinants 5,6. In 2005, the homicide rate in Brazil reached 27/100,000, being amongst the highest in the world 7. In 2012, Brazil accounted for approximately 10% of all homicides in the planet, thus being the country with the highest absolute number of homicides 1. This resulted from complex interactions between individual, relational, social, cultural, and environmental factors 8. Aiming to understand the association of these factors with homicides is an important step for public health to prevent the issue and consequently other common violence manifestations There is a growing need to understand socio-environmental conditions and their relations with the health-disease process. In 2005, World Health Organization (WHO) created the Commission on Social Determinants of Health 9. Its goal was to raise awareness on the influence of social determinants on the health of individuals and groups, as well as the need for taking actions. Thus, understanding these determinants is the first step to elaborate policies and proposing health equality 9. Based on the aforementioned circumstances, the purpose of this study was to understand the relations between socio-environmental determinants of health (SDH) and homicides in Brazil by performing a systematic review of literature. This review was based on previous studies 8,9 that indicate that structural elements of social stratification determine and condition social positions and strata, sharing socioeconomic characteristics, such as education, income, gender, among others. These elements may lead to vulnerability exposure and health damages in the form of diseases and accidents, which may also lead to violence and homicides 9. Despite SDH not having a linear cause-and-effect relation to homicides, this article aimed to systematically explore what recent studies present on the main social, economical, and environmental factors linked to homicides in Brazil. The following questions guided this systematic review: (1) which SDH are associated with homicides in Brazil?; (2) which SDH were analyzed regarding their impact and association with homicides in Brazil?; (3) which SDH were analyzed as protective factors in preventing homicides in Brazil?


Introduction
According to the 49th World Health Assembly, held in 1996 1 , violence is a public health issue that holds no consensus regarding the concepts, causes, and consequences of this complex subject.This study understood violence as a process of many historical causes that need to consider its cultural, economical, sociopolitical, environmental, and legal aspects in its analyses 2 .
Violence can manifest itself in different ways, including homicide, which is the pinnacle of violence, because it implies life annihilation.Homicides are the fourth main cause of death among people aged between 15 and 44 years old in the world 1 .This study understood "homicide" based on the Brazilian Criminal Code, which defines it as the act of killing another person, be it due to malice, when there are intent and awareness of results, or due to guilt, negligence, or recklesness 3 .Homicide is one of the most important violence indicators, and the one that most clearly depicts the magnitude and severity of the situation 2 .
Estimates show that in 2012 approximately 475,000 people were victims of homicides worldwide, a rate of 6.7 homicides per 100,000 inhabitants 1 .The rate in the American continent is 28.5/100,000, followed by Africa, with 10.7/100,000 1 .These rates did not evenly distribute homicides considering genders, age groups, and socioeconomic factors.Men represent 82% of the victims, with estimated rates 4 times higher than women 1 .The highest rates of homicide worldwide are among men aged between 15 and 29 years old (18.2/100,000) 1 .
In Brazil, since the 1980s, there has been a significant growth in homicide-related deaths, particularly in urban environments, with young black males mostly being both aggressors and victims 4 .Recent studies point out to social inequalities as one of its main determinants 5,6 .In 2005, the homicide rate in Brazil reached 27/100,000, being amongst the highest in the world 7 .In 2012, Brazil accounted for approximately 10% of all homicides in the planet, thus being the country with the highest absolute number of homicides 1 .
This resulted from complex interactions between individual, relational, social, cultural, and environmental factors 8 .Aiming to understand the association of these factors with homicides is an important step for public health to prevent the issue and consequently other common violence manifestations There is a growing need to understand socio-environmental conditions and their relations with the health-disease process.In 2005, World Health Organization (WHO) created the Commission on Social Determinants of Health 9 .Its goal was to raise awareness on the influence of social determinants on the health of individuals and groups, as well as the need for taking actions.Thus, understanding these determinants is the first step to elaborate policies and proposing health equality 9 .
Based on the aforementioned circumstances, the purpose of this study was to understand the relations between socio-environmental determinants of health (SDH) and homicides in Brazil by performing a systematic review of literature.This review was based on previous studies 8,9 that indicate that structural elements of social stratification determine and condition social positions and strata, sharing socioeconomic characteristics, such as education, income, gender, among others.These elements may lead to vulnerability exposure and health damages in the form of diseases and accidents, which may also lead to violence and homicides 9 .
Despite SDH not having a linear cause-and-effect relation to homicides, this article aimed to systematically explore what recent studies present on the main social, economical, and environmental factors linked to homicides in Brazil.The following questions guided this systematic review: (1)  which SDH are associated with homicides in Brazil?; (2) which SDH were analyzed regarding their impact and association with homicides in Brazil?; (3) which SDH were analyzed as protective factors in preventing homicides in Brazil?

Methodology
The protocol for this systematic review was registered under the International Prospective Register of Systematic Reviews (PROSPERO) of the University of York, under number CRD42017073557.The systematic review was conducted and presented according to the Preferred Reporting Items for

Types of selected studies
Studies of any kind of methodology (quantitative/qualitative) that analyzed homicides in Brazil and discussed their associations with SDH were included.Eligibility criteria for inclusion were: quantitative or qualitative studies on homicides in Brazil (1), whose methods included primary data collection or secondary data analysis (2), and were published between 2002 and June/2017 (3), in English, Spanish, or Portuguese (4).The year of 2002 was chosen as our starting point, because it was in that year that WHO has published the first main study on the impacts of violence on health 10 .Exclusion criteria were applied to studies that: did not approach homicides in Brazil (1), not included results or discussions about SDH and their association with homicides (2), presented reviews, opinion articles, case studies, editorials, policies, non-conventional literature, or conference abstracts ("grey literature") (3), were published in 2001 or before (4), and that focused on the psychological/ psychiatric state of perpetrators/victims instead of SDH (5), and on isolated/specific cases of mass homicides (serial killings, mass murders, or terrorism) (6).

Article tracking and selection
Two authors performed a double-blind review: a Ph.D. in Public Health and a doctorate candidate.Firstly, abstracts were independently tracked based on our research strategy (Box 1), and disagreements were solved with the support of a third author (Ph.D.).Causes for exclusion were registered for each article, as previously pointed out.Then, the studies that met the eligible criteria had its abstracts fully read (Figure 1).

Critical appraisal
There are several tools for assessing quality in systematic review.However, it is still a challenging process, considering there is no consensus about it.Being aware of its limitations, for this review, and following another systematic review 11 critical appraisal, we adopted the Critical Appraisal Skills Programme (CASP; http://www.casp-uk.net/casp-tools-checklists)checklist, which includes qualitative and quantitative study tools (randomized control trials, cohort, case-control, diagnostic studies, clinical prediction rule, and economical evaluation), following other recent systematic reviews 11,12,13 .For cross-sectional studies, which are not covered by the CASP, we adopted the Checklist for Analytical Cross-Sectional Studies by the Joanna Briggs Institute (http://joannabriggs.or/research/ critical-apparisal-tools.html).
Initially, each study was classified according to its study design.Then, each of them was analyzed according to specific items that compose the aforementioned tools, including: study aims analysis, if the study design was appropriate and aligned with its aims, if data was measured in a valid and reliable way, rigorousness of analysis, application of results, among other items.
Eligible studies were classified using critical appraisal instruments according to the quality of evidence on SDH: very low (unclear) when the two screening questions (Section A of CASP) were not satisfied; low when the total score was < 50%; moderate when total score was between 51% and 99%; or high when total score = 100%.

Box 1
Adopted boolean descriptors and operators.
Source: prepared by the authors, 2018.

Study management and storage
Resulting articles were stored and managed using the online version of EndNote (http://www.endnote.com),based on the following steps: (1) title and abstract reading of all the articles identified by the research strategy; (2) exclusion of duplicates and texts in other formats; (3) publication selection from 2002 onwards; (4) comparison between the two lists generated by independent researchers; (5) discussion involving these two researchers with the help of a third author, to reach consensus; (6) reading of full versions and critical analyses of the remaining articles.

Data collection and synthesis strategy
The collected data included title, authors, journal, year of publication, aims, study design, measures and outcomes, including quantitative and qualitative analysis of the SDH, which were grouped into Results were presented in a narrative synthesis 14 , categorizing its findings according to the most common SDH.A narrative analysis of each category was performed.As simply describing the studies is not enough to carry out a narrative synthesis, we adopted a textual approach that analyzes the associations implied in each study and the ones between studies, as well as an overall assessment of evidence rigorousness 14 .Following international guidelines for systematic review reporting, we also organized tables to provide a descriptive summary of the findings and explain study characteristics.

Results
After reading the full version of the 60 articles included in this review, we perfomed a narrative synthesis of results by categorizing the findings according to the following SDH: territory; race/ethnicity; gender; age group; social inequalities and economical factors; development; education; work and employment; drugs and trafficking; other SDH.Sections below will approach all SDH.The description of articles and its corresponding goals and SDH is in Table 1.
Critical appraisal showed that most studies (47/60) satisfied all items from the appraisal tools, thus being considered of "high quality".Around 13 out of 60 were considered of "moderate quality" with scores varying from 60-99%.Only four articles 15,16,17,18 had the lowest CASP score of 60% (6/10) and all of them were qualitative studies, mainly lacking information about data collection or ethics clearance (these results were less considered in our narrative synthesis).Based on our appraisal, no studies were considered of low or very low quality.

Territory
Issues concerning territory were the most common out of all SDH.For this review, the adopted concept of territory was that of a human and social construct that could be obtained from geographic occupation, or as a symbolic appropriation based on the identity of cultural groups that create the environment where they live 19 .
There were also other territorial approaches, such as the role of Brazil in the Latin American context 15,16,17,23,26,27,31,43,62,68 , or the context of specific Brazilian regions, such as the Amazon 33,34 , the Brazilian Southeast 69 or the Brazilian South 68 .
Studying the territory is essential to understand the dynamics of homicides.Studies suggested a higher rate of homicides in areas/territories of higher social vulnerability and lower quality of life in urban environments 5,6,7,29,31,33,42,50 .Social inequality seems to be one of the most popular justifications for the homicide epidemic (even more than poverty in absolute terms), being linked to urbanization issues and high populational growth 5 .However, it is not possible to associate homicides only with poverty, because rich cities and regions have also shown high homicide rates 38,48,65 .Instead, we should reflect on how urbanization and the reckless growth of cities/regions can cause social inequality and, consequently, be more closely connected to homicides.
For example, one of the studies focused on Maceió 42 , which is considered one of the capitals with the highest homicide rates.However, this study showed that despite homicides happening in all of its neighborhoods, the distribution of these occurrences is not even.Regarding territory, the research showed different regional patterns of armed aggression, hence indicating that there are regions where the population is more vulnerable to homicides, which points out to the need of considering urban inequality.
Another study about homicides and youth in Santa Catarina and Paraná 37 showed an increase in homicide rates in Brazilian borders with Paraguay and cities close to highways that connect the Paraguayan border with capitals and big cities in the South and Southeast regions of Brazil.It also showed that cities in the Brazil-Argentina were at a lower risk when compared to those from other areas.This situation can be explained by the association between violence and the trafficking of drugs, firearms, and other products in the border with Paraguay, in addition to relevant factors such as social inequity and the lack of special government policies for this region 37 .
The North, Northeast, and Central regions of Brazil are agricultural frontier areas prone to severe land tenure-related conflicts, with the highest rates of deaths due to homicide, whereas the South and Southeast regions, which are more densely populated and developed, showed the lowest rates 29 .

Race/ethnicity
The association between homicides and ethnic-racial issues is well documented in Brazil, showing that blacks and "mixed" race people represent most of homicide victims, which prompted the coining of the expression "genocide of the black population in Brazil" 40,49,64 .A total of 20 articles (33.3%) discussed ethnic-racial issues and their association with homicides.
A descriptive study carried out in Salvador between 1998 and 2003 with a sample of 9,626 deaths due to external causes showed that black individuals die earlier and lose 12.2 times more potential years of life because of homicides when compared to white individuals 64 .
A time series for homicides in Brazil from 2000 to 2009 showed that the black population represented 69% of homicide victims for this time period 30 .Blacks have a higher risk of death from homicide than white people, regardless of their level of education.Relative homicide risk increases in the black population and decreases in the white population, which suggests an increase in inequalities 30 .
This increase in homicides is due to the social and economical inequalities between regions, populations, rich and poor individuals, as well as between racial/ethnic groups 44,49,57 .This is directly associated with low income and education, and can also be associated with other types of violence, such as racism and discrimination 29,48,64 .A research on São Paulo youth map 59 showed that outskirt areas, which are poorer and have the worse living conditions, are also the ones with the highest concentration Cad.Saúde Pública 2018; 34(12):e00012818 of black population 59,61,64 .Therefore, ethnicity is an important indicator of social inequality, pointing to higher rates of death by homicide, as shown by various research 65 .
Nevertheless, it is worth to highlight that race/ethnicity is commonly linked to other SDH, which increases exposure to homicides.Skin color is a social marker of difference and racism is present in several levels in the Brazilian society.However, we outline the importance of reflecting on the SDH as a group of interconnected factors.In other words, whithout denying racism, what exposes people to homicides is not solely race/ethnicity, but racism alongside the socioeconomic context in which its victims live in 30,40,64 .
A study 30 with robust data indicated that mortality of the black population stems from low levels of income and education, while also possibly stemming from racism and discrimination, therefore inferring that these factors influence homicides in this population.Another challenging fact is the data that shows an increase of 28.6% in black victims of homicides between 2000 and 2009, whereas the number of white victims decreased by 24.5% in the same period 30 .

Gender
There is a huge difference in homicides rates concerning gender.Even after accounting for the studies' methodological variability, men were unanimously more susceptible to homicides than women, possibly up to 10 times more 50 .A total of 40 articles (66.67%) discussed the association between gender and homicides.
Between 2000 and 2009, homicide rates for white men were 10 times higher than for white women, whereas for black men it were three times higher than for black women 30 .Lifestyle, habits and social behavior, urbanization, and socioeconomic level can socially determine differences in homicide rates 17,36,40,65 .
Despite the number of women victims of homicide being lower than for men, one should not dismiss this issue, as there is need to consider the number of gender asymmetries.Whereas men are more prone to homicides on the streets, women are more killed inside their own home, in an allegedly safer environment 36,48,49 .Women homicides are greatly associated with intimate partner violence.Estimates show that 35% of women worldwide have already suffered from physical or sexual violence by intimate partners or sexual violence by non-partners 22 .
Many studies 20,22,28,36,48,49 call attention to femicide in Brazil, which consists of gender-based homicides from which women are victims just for being women 28,36 .Between 2003 to 2007, approximately 20,000 women died from femicide in Brazil, mostly young, single, of low education level 28 .Statistics suggest that woman homicide happens every two hours in Brazil, the 12 th country in the world ranking of women homicides 29 .
Unequal gender relations culminate in men's dominance over the body and life of their partners, as an expression of male hegemony, aggressiveness, and macho-culture 28,36,48 .Macho-culture and misogyny are the results of a patriarchal system that predispose violence and feminicide 36 .Moreover, other SDH intersect gender issues and exponentiate the problem, such as the use of legal drugs (alcohol) and illegal drugs by the perpetrator 34 , as well as race/ethnicity issues (homicides are more common among black women than white women) and socioeconomic factors (exposure of poor women is more significant than in rich women) 30,46,57,61 .

Age group
Homicides in Brazil are the main cause of premature death, directly affecting the lives of young people 32,43,56,63 .Out of 60 articles, 39 (65%) discussed age group issues and their association with homicides.
Studies show that violence is a factor that leads to early death of young people, preventing them from enjoying economical development in the country in the last decade 32 .They also indicate that young men aged between 15 and 39 years old are the main victims and perpetrators of homicides, mostly due to social inequalities 42,70 .Much of this results from the exclusion from formal education, lack of employment and of future prospects.As homicides do not occur evenly among distinct ages, the age group from 15 to 39 years is the most vulnerable one.However, age groups should Cad.Saúde Pública 2018; 34(12):e00012818 not be analyzed separately from other SDH.In addition to age, economically unfavorable environments can impact individuals and contribute to violence, poverty, and social exclusion, leading to homicides 5,17,21,24,37,42 .

Social inequalities and economical factors
Homicides have a strong social meaning, not only because they take away life, which is a right of every citizen, but also because they are a reflex of the problems faced by our society, such as inequalities, impunity, corruption, among others 50 .Out of 60 articles, most of them (n = 51 or 85%) discussed social inequalities or economical factors and its association with homicides.
Studies showed a strong relation between homicides and quality of life issues, highlighting their direct association with social inequity 27,41,58 and youth unemployment 17 .Unfavorable socioeconomic conditions may lead to social and health inequalities.Social disadvantages play a prominent role in homicide rates 37,41,47,62,66 .People that live in poorer areas with limited access to public facilities are more prone to higher homicide rates 35,38,52,69,70 .
As population grows, income inequality becomes an important factor for homicides 38 .Social inequality is more than economical inequality; poverty is not the problem itself, but the so-called relative poverty, which prevent some people who live under unfavorable conditions from having specific opportunities 18,30,38 .
A study on social inequality showed that groups from cities with more income inequality (i.e. a higher Gini index) have higher homicide rates 37 .For most social indicators, there was a lower risk of homicide for groups from cities with more favorable conditions, with lower unemployment and illiteracy rates and fewer people and children living in extreme poverty 37 .
Studies 18,23,24,35,45,51,60 indicated that income or wealth alone is not enough to explain homicides, neither to adopt interpretations in which the socioeconomic environment determines the behavior of an individual.Poverty by itself cannot explain the high risk of homicides for vulnerable groups.One should highlight that issues concerning social inequality, injustice, exclusion, populational growth, inefficient government, altogether, seem to be responsible for the rise of homicides in Brazil 18,23,24,35,45,51,60 .
However, income seems to be a protective factor against homicides.A study on the determinants of homicides in Bahia showed a direct association between the amount of people who received Brazilian Income Transfer Program (Programa Bolsa Família) grants and homicides, indicating that areas that receive more help from the government are the ones with more social protection resources 24 .Another study from the state of São Paulo correlates the homicide mortality coefficient and independent variables, pointing out to how this coefficient increases as income decreases 60 .When measuring income as a natural logarithm, there was an increase of 1% in income results in an expected decrease of 0.695 in homicides, showing how directly and significantly income impacts homicides 45 .

Development
The concept of development is complex, and we do not aim at discussing it.We wanted to point out studies on the association between development and homicides, accounting for 18 studies (30%).
The stagnation of Brazilian economy in the 1980s hindered income inequality, which has been associated with an accelerated urbanization process since previous decades.Most of the population moved from rural areas to city suburbs, without having access to adequate infrastructure services.Consequently, the growth of youth population since the 1960s and the ensuing high rates of unemployment and informal jobs (mainly for people with low levels of education) also contributed to the increasing homicide rates 29,57 .
The lack of decent urban development, mainly in the suburbs of large cities, has been contributing to less policing, worse public lighting, and insufficient public transportation, thus further exposing people who live in these areas to violence and homicides 6 .Therefore, this need for local development and decent public equipment can contribute to organized crime settling (particularly regarding drug and firearm trafficking) where the government is less present, thus leading to more homicides 6 .

Education
Social inequality and institutionality levels are variables that determine a higher prevalence of homicides 25,43,53 .Out of 60 studies, most of them 33 (55%) dealt with education-related issues as potential determinants of homicide.
People with a lower level of education represent the largest group of homicide victims, regardless of race/skin color, when compared to victims with a higher level of education 29,35,49,64 .Education can significantly reduce the risk of homicide, being considered an important protective factor 29,35,39,54 .However, once again, it is not possible to analyze education level separately, as a low level of education can stem from a low socioeconomic level, and consequently to higher exposure to violence and homicides 6,24,30,48,57,60 .A highly educated population presents lower homicide rates and other criminal activities, as it ensures better job and income prospects, while also giving young people an occupation and preventing them from criminal activity 20,45,46,48 .
A study on homicides in the state of São Paulo 60 suggested a correlation between the homicide mortality coefficient and independent variables, pointing out to how this coefficient increases as education and income levels decrease.Additionally, the increase in the amount of illiterate people with more than 15 years of age is connected to higher coefficients of death due to homicide.

Work and employment
SDH also includes work and employment, but its results were not very conclusive; studies usually focus on discussing income rather than discussing work and employment themselves.For example, a study stated that an increase in the income logarithm results in a decrease of 17.92 in the homicide rate 6 .Different studies showed that intersections of different variables, including (un)employment, are decisive for homicide mortality, such as intersections with income (bad distribution) and low levels of education 35 .Another potential determinant was social disorganization theory as it correlates the lack of employment and social problems, which may lead people to crime 35,50 .Another study suggested that, among Brazilian states, unemployment is negatively associated with suicide, but positively with homicide 34 .
Regarding work and intersections with other SDH, homicides seem to be more common among disadvantaged groups from urban territories with unfavorable employment, income, education, and housing issues 48 .Income inequality, differences in the access for distinct populational groups, and poor social resources can determine the degree of violence in each region 18,19,65 .On the other hand, a higher number of formal job opportunities prevents youth from crime, especially trafficking, resulting in the decrease of homicide rates 56 .

Drugs and trafficking
In Brazil, there is a direct association between homicides and drug/firearm trafficking, a powerful economical sector which employs coercion, threats, and executions as land control mechanisms and disputes over drug-selling locations 50 .A total of 26 studies (43.3%) approached drugs and trafficking as potential homicide-related SDH.
Drug trafficking is responsible for a high number of homicides caused by the corroding penal code established by traffic, which has led young family members from poor neighbourhoods, to death; the bloody competition between drug dealers over profit; and conflicts with the police, including sometimes corrupt policemen that demand a share of their profit 61 .
Nevertheless, Brazil cannot be analyzed separately from the Latin American context, particularly regarding this SDH.Latin America presents the highest homicide rates 1 and is infamous for being as an illicit drug manufacturer involved in international trafficking.It is important to understand how neighboring countries have been studying and dealing with this issue to promote joint actions.A Colombian study analyzed the extraordinarily high homicide rates in the country and was able to identify three structural causes for it: inequality, impunity, and intolerance, as well as three transition processes, namely drug trafficking, internal armed conflicts, and the introduction and development of a neoliberal model 2 .
Cad. Saúde Pública 2018; 34 (12):e00012818 The increase in homicide rates has been connected to social inequality, the rise in misery and poverty, the inefficiency of the legal system, growing impunity, spread of organized crime, governmental corruption, easy access to guns, and drug trafficking 67 .Land disputes for drugs trafficking and conflicts with the police favor the high number of homicides 51,61 .Between 1991 and 2000, the proportion of homicides with firearms had a 50% increase due to the use of guns trafficked by organized crime 29 .Between 2000 and 2009, Brazil reduced the number of deaths from firearms after implementing the Disarmament Statute and national campaigns for voluntary firearm surrender in 2004 30 .According to data from 2007, guns had been used in 71.5% of deaths by homicide 29 .

Other SDH
Between 2000 and 2009, there was a significant decline in homicide rates in the state of São Paulo.A factor which could partly explain this decline, besides the aforementioned Disarmament Statute, is the rise in the arrestment of criminals 30,39,56 , which theoretically caused a decline in homicides by preventing new homicides 7,30,39 .
Despite corruption in politics also contributing to the number of homicides, as it foments the lack of confidence in government institutions 15 , there is a lack of rigorous studies addressing this issue.
Studies also mentioned other SDH that could be associated with homicides in Brazil.However, the quality of data produced for these other determinants was not relevant for this systematic review according to their quality assessment.Therefore, to avoid speculation, we have limited our discussion to the aforementioned SDH, despite being aware that they are not enough to thoroughly explore the subject.

Protective factors
One might consider these systematic review highlighted items as protective factors against homicide as they are present in lower homicide rate contexts.Some of these factors have already been discussed, such as economic equality, less social inequality and the improvement of social indicators 6,20,68 .Differently from demographic density, which assesses the level of urbanization of a certain city, the average number of citizens per household defines family composition.In this sense, family composition seems to act as a protective factor against homicides in countryside cities, where the average number of people per household is higher 24 .
Regarding education, very few studies associate the people's education level with lower crime rates, although it has been noticed that higher education levels may significantly reduce homicide risk 18,30,38,62 .Considering this relation, it is possible to infer that education plays a major role in directly reducing homicide levels.Education can significantly reduce homicide risks, thus being an important protective factor 29,35,49,64 .However, it is not possible to analyze an item in isolation from other SDH, since a lower level of education can be connected to a lower socioeconomic level, and thereby connected to a higher level of exposure to violence and homicides 6,24,30,48,57,60 .
The Disarmament Statute possibly reduced the homicide rate for the white population, but for the black population, this rate increased, which suggests these efforts were less effective for the latter group 30 .Therefore, race/ethnicity is able to predict part of the profile of homicide victims; the increase in inequalities shows how Brazilian public policies are only partially effective in controlling violence, not approaching specificities that characterize such a diverse population.

Discussion
This systematic review focused on the association between SDH and homicides in Brazil.The main determinants concerned territory; race/ethnicity; gender; age; social inequality and economic factors; development; education; work and employment; drugs and trafficking; among others.Intersection of these factors is quite present, sometimes hindering the development of a narrative synthesis of these categories individually.On the other hand, some protective factors against homicides have been Cad.Saúde Pública 2018; 34(12):e00012818 found, such as higher levels of education and income, lower levels of social inequality, and recent public policies, such as the Disarmament Statute.
This review indicates that homicides are present in various macro and microregions of Brazil, despite not being evenly distributed.Homicides have been rising over the last years, both in capitals/ metropolitan areas and smaller cities 38 .Regions undergoing anaccelerated urbanization process coupled with insufficient, unequal and reckless economic development seem to account for the largest portion of homicides 24,34,37,42,50 .Assimilating territorial characteristics connected to the highest risks of homicides among specific groups (particularly men, young people, and black people) is a way of identifying the most vulnerable ones and developing targeted public policies 5 .We found a greater focus on the black population (the majority of victims), and a lack of studies on other ethnic minorities who also live under unequal conditions, such as indigenous people or immigrants.Understanding and making these information public alongside its territorial variations is challenging and a promising way of improving public health 16,26,55 .
Based on this systematic review, we believe it i paramount to reflect on the future of youth, particularly black youth, which frequently faces poverty, exclusion, and lack of opportunities and safety.In certain regions, this may lead young people, especially men, to turn themselves to crime as a profitable and economically attractive option 50 .Which would, lead to increased exposure to violence and even to homicides.Despite the number of studies on the association between poverty, inequity, and violence, its results do not always follow the same directions, presenting discordant conclusions 60 .A study carried out in Bahia 24 indicated how income or wealth alone is not enough to explain homicides.These data are important to prevent prejudiced associations between poverty, violence, and homicides.Some poorer Brazilian states, such as Piauí, have low homicide rates when compared to wealthy states, such as Paraná 21,30 .Even in Paraná, wealthy regions such as the metropolitan area of Curitiba show higher homicide rates when compared to poorer areas of the same state 27,37,38 .There is need to interpret these data carefully to avoid associating homicide with income or poverty alone, also considering social inequality, which prevents people from certain opportunities.Intense exclusion seems to make individuals vulnerable, contributing to violence and homicides 6 .
These systematic reviews had many limitations, such as the diversity of methodologies employed by the eligible studies, as well as the quality and rigorousness of the accessed data, which made the conduction process quite challenging.This heterogeneity made it impossible for us to conduct a meta-analysis.The most critical limitation was that very few studies included nationwide or long time-series analyses.Most of them included local analysis and/or only approached a short time period.The CASP tool for critical appraisal was also a limitation.Space limitations also made the synthesis quite challenging, which might have left some information out.On the other hand, the methodological design proposed by the authors was a positive aspect that had been already previously established and that facilitated the systematic review conducting according to the PRISMA protocol.
We also detected some gaps in Brazilian research compared to an international study 71 on the same subject.The Brazil's legal context being one of them 2 , mainly when it comes to the ineffiency of the penal system and its inability to solve this problem.Political factors, particularly corruption, impunity, and political intolerance (which consequently lead to a disbelief on the legitimacy of government and its institutions), are associated with the spread of homicides in other Latin American countries 2 .Nevertheless, only a few studies 40,41,50 drew a connection between homicides and the Brazilian political situation, the slowness of its legal system, the deterioration of public security, or the devaluation and corruption inside these institutions, besides the decline in their ethical values.All these topics would be paramount for new studies, considering its urgency for Brazilian contemporary society.

Figure 1 Fluxogram
Figure 1Fluxogram showing the screening and selection process of articles, based on the PRISMA protocol.
10 categories: territory; race/ethnicity; gender; age group; social inequalities and economical factors; development; education; work and employment; drugs and trafficking; other SDH.

Table 1
Studies included in the systematic review according to year, author(s), title, goals, and socio-environmental determinants of health (SDH).

Table 1 (continued)
24 (2014)To evaluate the risk of homicide in Rio de Janeiro's favelas, taking into account the territorial disputes taking place in the city.Territory, drugs and trafficking.Moderate qualitySouza et al.24(2014) Tocarry out a study on the association between socioeconomic and demographic factors and homicides from general population, in the state of Bahia, in 2009.Territory, gender, age group, social inequalities and economic factors, development, education, work and employment. 36(2014) This study aimed to assess the female homicide rate due to aggression in Rio Grande do Sul, Brazil, using this as a "proxy" of femicide.Cad.Saúde Pública 2018; 34(12):e00012818

Table 1 (continued)
54(2012) The scope of this study was to analyze the association between homicides and public security indicators in São Paulo between 1996 and 2008, after monitoring the unemployment rate and the youth proportion in the population.Work and employment.High quality Briceño-León 16 (2012) This study analyzes and compares the changes occurred in Colombia, Venezuela and Brazil in the first decade of the twentyfirst century, where the homicide rate has decreased, increased and remained the same, respectively.Cad.Saúde Pública 2018; 34(12):e00012818