The global decline of births from 1990 and 2015 has to a reduction in the proportion of people aged 15-29. So might this explain why the world’s homicide rate has dropped by nearly 20%? In episode 64, we’re joined by Mateus Rennó Santos from the University of South Florida. He talks with us about his research into how an aging population is a driving force behind the decline in homicide that most countries across the globe have enjoyed for the past three decades. His article, “The contribution of age structure to the international homicide decline,” was published with Alexander Testa, Lauren Porter, and James Lynch on October 9th, 2019 in the open access journal PLOS One.

Global Decline of Homicide - Mateus Rennó Santos
Global Decline of Homicide - Mateus Rennó Santos
Global Decline of Homicide - Mateus Rennó SantosGlobal Decline of Homicide - Mateus Rennó Santos
@rwatkins says:
Next time, in episode 65 of Parsing Science, we’ll be joined by Luke Chang from the Department of Psychological and Brain Sciences at Dartmouth College. He’ll discuss his research into socially transmitted placebo effects, through which patients can pick up on subtle facial cues that reveal their doctor's beliefs in how effective a treatment will be.
@rwatkins says:
Mateus and his colleagues found that a one percentage point increase in the proportion of youth in a population was associated with an increase in the homicide rate of 5.4%. So, a big takeaway from the paper for us was that demographic patterns deserve special attention in explaining homicide trends. We finished our conversation by asking Mateus what he believes the broader implications of their findings are.
@rwatkins says:
With data spanning nearly 70 years across multiple countries, inevitably, some data points were missing in the UNODC and WHO’s materials. However, statistical techniques allow for “imputing” missing data with substitute values derived from the data that are available. Mateus explains next how he and his team applied this technique in their study.
@rwatkins says:
While demographic variables can be controlled for in a statistical analysis, conditions that produce higher crime rates - such as those related to political, social, and economic distress - might also account for the decrease in homicide among an aging population. So Doug and I asked Mateus how these variables were accounted for.
@rwatkins says:
As Mateus mentioned earlier, just as a population’s average age relates to its homicide rate, so too does a country’s income inequality and its relative safety and security. But since there could be many other factors that explain the associations between these variables, we were curious how potential confounds were adjusted for in the project.
@rwatkins says:
While the UN dataset tracked 126 of the world’s countries with more than 1 million residents in 2015, the data only capture homicides since 1990. Conversely, the W H O Mortality Database captured homicide data since 1950, but for a much smaller set of countries. So Doug and I followed up by asking Mateus about the extent to which the data were representative of all the world’s nations … or of only a few.
@rwatkins says:
Mateus and his colleagues triangulated their data from two sources: the United Nations Office on Drugs and Crime, or UNODC, and the World Health Organization, or W H O. As the data spanned nearly 70 years, Ryan and I were interested in what this breadth of data allowed for ... that’s less available when looking at a more constrained period of time.
@rwatkins says:
While homicide is projected to cause more deaths globally by 2030 than infectious diseases such as tuberculosis, it’s also true that - nearly every year since the turn of the 21st century - more people have been murdered than have lost their lives to war. Mateus helps us understand this seeming paradox after this short break. [ad] This episode is brought to you by Altmetric. At Altmetric we help researchers track and analyze the online activity around scholarly research outputs. And if you like Parsing Science, you may also enjoy our podcast series, The Altmetric Podcast. Join me, Lucy Goodchild, as we explore the science stories that are being discussed the most online, so you can find out why. You can find our show on Soundcloud, Apple Podcasts, Google Podcasts, or wherever else you listen to podcasts. Now, back to Parsing Science.
@rwatkins says:
Mateus and his colleagues decided to use long-term longitudinal data to examine if - and how - changes in age-structure corresponds to homicide. So Ryan and I were curious whether the same factors responsible for fluctuations of homicides within countries might also be at play between them as well.
@rwatkins says:
The world’s population of young people peaked in the 1960s and 70s, then - from 1980 onward - all regions except Africa experienced a decline in their population of people 15 to 29 years of age. Also during this time, the average global life expectancy increased from 43 to 66 years. Since homicide rates declined concurrently with these worldwide trends, Mateus was curious whether global aging might be related to the international decline in homicide, as he explains next.
@rwatkins says:
While homicide is one of the world’s leading causes of premature death globally - accounting for about 400,000 deaths each year - what differentiates a homicide from other similar causes of death, such as manslaughter, isn’t always clear. So Ryan and I began our conversation with Mateus by asking him to explain how homicide is defined around the world.
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Hosts / Producers

Doug Leigh & Ryan Watkins

How to Cite

Leigh, D., Watkins, R., & Santos, M. R.. (2019, December 10). Parsing Science – Global decline of homicide. figshare. https://doi.org/10.6084/m9.figshare.11356400

Music

What’s The Angle? by Shane Ivers

Transcript

Mateus Rennó Santos: Most of the world has been getting a lot safer since the 1990s, and an international homicide decline exists.

Doug Leigh: This is Parsing Science: the unpublished story is behind the world’s most compelling science, as told by the researchers themselves. I’m Doug Leigh.

Ryan Watkins: And I’m Ryan Watkins. Today, in episode 64 of Parsing Science, we’re joined by Mateus Rennó Santos from the Department of Criminology at the University of South Florida. He’ll discuss his research into how an aging population may be the driving force behind the reduction in homicide that countries in North America, Europe, Asia, and Oceania have enjoyed over the past three decades.

Santos: Hi, thanks for having me. I’m Mateus Rennó Santos. I’m originally from Brazil, and six years ago I finished my masters in sociology in the Federal University of Minas Gerais, and I was working there – I was working with research – on a crime research center. My job was to take a look at policing data – police records of homicides – and just to see if they were actually homicides, and to generate, like, this official count of homicides. But I felt that I was not done with studying; I had my Master’s, but I wanted more. So what I did is that: I wanted to come to the United States to do my PhD, and I Googled “best criminology programs in the world,” and I applied to the top two. I applied to the University of Albany, and I applied to Maryland. Albany rejected me, and then I thought, “Okay, that must mean – probably means – I’m not competitive.” And then Maryland accepted me, and I left everything, and I came. And I spent one year in Austria collecting the data a for my dissertation, which we’re going to talk about. I was a consultant for the United Nations Office on Drugs and Crime, specifically for the Global Study on Homicide. So I counted homicide when I was in my home state, right? Six years after I helped the United Nations count all homicides in the whole planet. I came back to finish my PhD and to go to the academic job market, and I was very lucky to find a position here at the University of South Florida in the Department of Criminology, and I’m loving it. It’s great; was worth it.

Leigh: While homicide is one of the world’s leading causes of premature death globally – accounting for about 400,000 deaths each year – what differentiates a homicide from other similar causes of death, such as manslaughter, isn’t always clear. So Ryan and I began our conversation with Mateus by asking him to explain how homicide is defined around the world.

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