My eye was caught by a paper, summarised in the BPS Research Digest of 17th March, on the relationship between low resting heart rate and crime. The conclusion was that adolescents with low resting heart rate were more likely to go on to commit crimes, including violent crimes, possibly because they did not get too fussed when attacking others. Cool, calm, collected and lethal. All this takes place in the city of Pelotas, Rio Grande do Sul, Brazil.
Low resting heart rate is associated with violence in late adolescence: a prospective birth cohort study in Brazil. Joseph Murray, Pedro C. Hallal, Gregore I. Mielke, Adrian Raine, Fernando C. Wehrmeister, Luciana Anselmi and Fernando C. Barros. International Journal of Epidemiology, 2015, 1–10 doi: 10.1093/ije/dyv340
Abstract Background: Youth violence is a major global public health problem. Three UK and Swedish studies suggest that low resting heart rate predicts male youth violence, but this has not been tested in other social settings nor for females. Methods: A prospective, population-based birth cohort study was conducted in Pelotas, Brazil. Heart rate was measured using a wrist monitor at ages 11, 15 and 18 years. Violent crime and non-violent crime were measured at age 18 in self-reports and official records (N=3618). Confounding variables were assessed in the perinatal period and at age 11, in interviews with mothers and children. Logistic regression was used to estimate associations between quartiles of heart rate at each age, and violent and non-violent crime at age 18, separately for males and females. Results: Lower resting heart rate was a robust correlate of violent and non-violent crime for males. Comparing males in the lowest and top quartiles of heart rate at age 15 years, adjusted odds ratios were 1.9 for violent crime [95% confidence interval (CI) 1.4–2.7] and 1.7 for non-violent crime (95% CI 1.1–2.6). For females, crime outcomes were associated only with low resting heart rate at age 18. Associations were generally linear across the four heart rate quartiles. There was no evidence that associations differed according to socioeconomic status at age 15. Conclusions: Low resting heart rate predicted violent and non-violent crime for males, and was cross-sectionally associated with crime for females. Biological factors may contribute to individual propensity to commit crime, even in a middle-income setting with high rates of violence.
This looks good. A birth cohort of good size, repeated measures, and a prospective basis for judging an important behaviour: violence. In addition to repeatedly measuring heart rate and checking public records for offences (and also looking at self-reports) the authors measured the following:
Confounding variables. The following variables were measured in the perinatal period in interviews with mothers: unplanned pregnancy (yes/no), mother smoked in pregnancy (yes/no), maternal alcohol use in pregnancy (yes/no), maternal age (years), number of siblings, maternal education (years of schooling) and family income (minimum wages per month). All were previously found to be associated with violence at age 18 years for men or women in this sample. Self-reported skin colour was measured and categorized as white, black, mullato/brown, yellow and indigenous. The following participant characteristics were measured at age 11 years: smoking (yes/no), drinking (yes/no), physical activity (min per week in leisure time physical activity and active transportation to/from school), height (centimetres), weight (kilograms), and blood pressure (mmHg continuous). Maternal mental health was also measured when participants were aged 11, using the Self Report Questionnaire (SRQ), previously validated in a Brazilian sample of 485 subjects.22 The continuous SRQ score from 0 to 20 was used in the analyses.
The results: The prevalence of violent crime at age 18 was 26.6% among men and 11.3% among women (P < 0.001). Equivalent figures for non-violent crime were 14.8% and 5.8%, respectively (P < 0.001). Among those who committed violence (N= 679), less than half (44%) also committed a non-violent crime; by contrast, among those who committed non-violent crime (N ¼ 367) the vast majority (82%) also committed violence.
The prevalence of violent crime was 34% among men in the first quartile of heart rate (low heart rate) at 15 years, whereas it was 20% among those in the fourth quartile (high heart rate). Equivalent figures for non-violent crime were 19% and 12%, respectively.
This is an enormously high rate of violence, which needs some explanation. Within that violent population, those with low heart rates are even more violent, a significant increase in proneness to violence.
The authors go on to observe in their discussions:
The key finding of this study is that lower heart rate was a robust predictor of male violent and non-violent crime. Although only cross-sectional associations were found for females, prospective and concurrent associations were observed for males after adjusting for a range of confounding variables. The main strengths of the study were: (I) the use of a large prospective community cohort; (ii) the repeated measures of heart rate; (iii) the multiple measures of crime; (iv) the inclusion of females as well as males; and (v) the wide range of confounding variables included.
It should also be considered that the current study was conducted in one Brazilian city, and results should not be generalized to the rest of the country. Pelotas is a relatively poor city in a relatively rich southern state of Brazil. When crime data were collected for this study in 2011, there were 18.9 homicides in Pelotas per 100 000 population, lower than the national rate of 27.1 but considerably higher than in England and Wales (1.3) and Sweden (0.9) where previous studies of heart rate and violence have been conducted.
So, something raises the level of violence in Brazil 30 times above Sweden, and 21 times above England and Wales. In the grizzly list of the 50 most dangerous cities in the world, Brazil accounts for 21 of them and Pelotas, violent as it is at 19 homicides per 10,000, is not one of them. Here they are, so have a quick scan and see if any patterns present themselves:
The 50 Most Violent Cities in the World 2015
Rank City Country Homicide Rate/10,000
1 Caracas Venezuela 120
2 San Pedro Sula Honduras 111
3 San Salvador El Salvador 109
4 Acapulco Mexico 105
5 Maturín Venezuela 86
6 Distrito Central Honduras 74
7 Valencia Venezuela 72
8 Palmira Colombia 71
9 Cape Town South Africa 66
10 Cali Colombia 64
11 Ciudad Guayana Venezuela 62
12 Fortaleza Brazil 60
13 Natal Brazil 61
14 Salvador (y RMS) Brazil 60
15 St. Louis U.S.A. 59
16 João Pessoa (conurb)Brazil 58
17 Culiacán Mexico 56
18 Maceió Brazil 56
19 Baltimore U.S.A. 55
20 Barquisimeto Venezuela 55
21 São Luís Brazil 53
22 Cuiabá Brazil 49
23 Manaus Brazil 48
24 Cumaná Venezuela 48
25 Guatemala Guatemala 48
26 Belém Brazil 46
27 Feira de Santana Brazil 46
28 Detroit U.S.A. 43
29 Goiânia Brazil 847 43
30 Teresina Brazil 42
31 Vitoria Brazil 42
32 New Orleans U.S.A. 41
33 Kingston Jamaica 41
34 Gran Barcelona Venezuela 40
35 Tijuana Mexico 39
36 Vitória da Conquista, Brazil 38
37 Recife Brazil 38
38 Aracaju Brazil 38
39 Campos dos Goytacazes Brazil 36
40 Campina Grande Brazil 36
41 Durban South Africa 35
42 Nelson Mandela Bay South Africa 36
43 Porto Alegre Brazil 35
44 Curitiba Brazil 35
45 Pereira Colombia 33
46 Victoria Mexico 31
47 Johannesburg South Africa 30
48 Macapá Brazil 30
49 Maracaibo Venezuela 29
50 Obregón Mexico 28
(The usual disclaimers apply: in places which are really, really violent there are few people left standing to stick around and count the bodies. That is done later by other techniques, if ever at all. Over lunch a few years ago John Sloboda explained to me how he calculated the body count in Iraq.)
However, within bodily error, the list gives pause for thought. Central America, South Africa, Brazil and USA all figure prominently. In that latter democracy St. Louis, Baltimore, Detroit, and New Orleans are very violent. Whatever the reason, it would be prudent to check whether the same reason may apply in Pelotas.
The authors conclude:
It is a striking conclusion that an individual-level biological characteristic, such as heart rate, is associated with crime in a Brazilian sample, given the high levels of serious violence in Brazil. One might speculate that individual level factors would be irrelevant in this social context, because of major socio-cultural drivers of crime and violence, including poverty, inequality, gangs, drug trafficking and corrupt and under-resourced criminal justice systems. However, the current study demonstrates that, even in this setting, a fully integrated biopsychosocial understanding of violence is required.
This paper does many good things, as far as it goes, so I wanted to push it further. The authors are willing to consider biological causes of crime, which is a good thing. What would an integrated bio-psychological understanding of violence involve? When reading a paper I ask myself whether the authors been psychologists, and whether they tested people for intelligence and personality, and if not, why not? These measures are not mentioned in the paper. Perhaps they were not included in the original study. If so, it is a great pity, because we psychologists must get ourselves together. Doctors measure blood pressure: can’t psychologists measure intelligence and personality, the most psychological aspects of people?
Also, I think one needs to sort out the genetics. I have looked in the supplementary tables, and also contacted the lead author to see if there may be further analyses either available or planned on the racial composition of these adolescents. Skin reflectance measures were taken, but appear to have contributed nothing to crime rates. This is worthy of publication itself. In the absence of data and discussion, here are a few pointers.
First, there is some evidence that heart rates vary by racial background.
Emergence of Ethnic Differences in Blood Pressure in Adolescence The Determinants of Adolescent Social Well-Being and Health Study. Seeromanie Harding, Melissa Whitrow, Erik Lenguerrand, Maria Maynard, Alison Teyhan, J. Kennedy Cruickshank, Geoff Der
Abstract—The cause of ethnic differences in cardiovascular disease remains a scientific challenge. Blood pressure tracks from late childhood to adulthood. We examined ethnic differences in changes in blood pressure between early and late adolescence in the United Kingdom. Longitudinal measures of blood pressure, height, weight, leg length, smoking, and socioeconomic circumstances were obtained from London, United Kingdom, schoolchildren of White British (n692), Black Caribbean (n670), Black African (n772), Indian (n384), and Pakistani and Bangladeshi (n402) ethnicity at 11 to 13 years and 14 to 16 years. Predicted age- and ethnic-specific means of blood pressure, adjusted for anthropometry and social exposures, were derived using mixed models. Among boys, systolic blood pressure did not differ by ethnicity at 12 years, but the greater increase among Black Africans than Whites led to higher systolic blood pressure at 16 years (2.9 mm Hg). Among girls, ethnic differences in mean systolic blood pressure were not significant at any age, but while systolic blood pressure hardly changed with age among White girls, it increased among Black Caribbeans and Black Africans. Ethnic differences in diastolic blood pressure were more marked than those for systolic blood pressure. Body mass index, height, and leg length were independent predictors of blood pressure, with few ethnic-specific effects. Socioeconomic disadvantage had a disproportionate effect on blood pressure for girls in minority groups. The findings suggest that ethnic divergences in blood pressure begin in adolescence and are particularly striking for boys. They signal the need for early prevention of adverse cardiovascular disease risks in later life. (Hypertension. 2010;55:1063-1069.)
In the light of these findings, it would be good to see the blood pressure measures in this paper broken out by ethnic group. To my eye the differences aren’t very big, but it is worth checking. Also, there are skin luminosity findings and self reports of racial identification, but those are not shown in the paper, nor in the supplementary tables. This is a significant omission, but easily rectified. Null findings should get publicity.
Second, it would be relevant to look at the rates of violence by ethnic group. In other parts of the world these vary widely, at least six-fold. It would be important to see whether Brazil conforms to this pattern, or is an exception. The best validated data comes from the US, and currently I do not know of comparable Brazilian data.
Since the US and Brazil have had different histories as regards race, with the latter being far more relaxed about inter-marriage, so the contrast is potentially informative. As far as I can see, the outcomes for Africans should be better in Brazil, because they were subjected to less racial discrimination. However, the violence rates in the above table suggest that my hypothesis about the effects of racial discrimination is wrong.
As to what it is like to live in Pelotas, a lady friend writes:
Yes, there is violence here in Pelotas and has been for years. I was assaulted at the front gate of my condominium by 2 young boys on a motorbike with a gun. Luckily one of my neighbours had just come in from his farm and the kids saw him, took my briefcase and left. From then on violence has grown to frightening levels, although one learns to live with it. To what level? Well, there is a restaurant a block away from my building and when I go there at night, I take my car as there is no way I would walk one block in the dark back home. When I go out at night to friend’s or restaurants I usually go in a taxi and come home in one as the driver waits for me to get into the condominium. If I go by car, on getting home I’m a sitting duck as I wait for the gate to open and close.
As for your question about “which adolescent boys/men are violent to whom”, I don’t have precise research data, but there are a lot of men being violent to women and kids, although we have had the “Maria da Penha law” for years (My note: legislation seeking to prevent domestic violence). Other laywoman remarks are:
– poor black boys are violent to just about anyone, mostly involved with drugs (I think).
– poor men black and white … To whom? As an exact thing, I don’t know… Just about anyone.
I contacted this friend without knowing this part of her history, and the above remarks are shown verbatim.
A 2005 survey gives the Pelotas population figures as 280,897 whites, 34,172 blacks, 25,395 of mixed ethnicities, 998 native Brazilians, 498 Asians, and 998 of unknown ethnicity. The 1993 birth cohort sample probably conforms to these proportions. These are sufficiently large for violence rates to be compared, particularly when the overall rate is so high.
Happily, we have other estimates of the European fractions of Brazilian states, and those also have intelligence estimates (Fuerst and Kirkegaard 2016). As a general rule, lower intelligence is usually associated with higher crime. This is not just because they get caught, because it also shows up on self-report.
The State of Rio Grande do Sul, in which the city of Pelotas is situated, is 79% European 9.5% African and 11% American Indian. The estimated IQ is 87.5 which is high for Brazil, but low in international terms, and consistent with poorly organised states and higher crime rates. Since Pelotas is described as a poor city in a rich state, one might assume that the ability levels were even lower than the state average.
So, one might hazard a guess that some mixture of intelligence and personality is causally involved in crime and violence. Whether heart rate is the most powerful of the biological measures remains to be seen, and is worth testing against broader biological measures like population stratification.