How the World Gets Sick and Dies

The results of a project to quantify and understand how human illness is changing on a global scale

"Caveman Chuck" Coker/Flickr

The Manhattan Project created the atomic bomb through an unprecedented combination of brainpower and money. Fifty years later, the same model helped the Human Genome Project map our genetic code. The ambition of these projects was matched only by the public hoopla surrounding them. But last month, with little fanfare, public health revealed its own foray into "Big Science": the Global Burden of Disease.

At its most basic level, the Global Burden of Disease addresses three questions: what makes people sick; how sick does it make them; and what causes people to die? To answer these questions, 486 researchers around the world came together to make model of the world's health. The report, published last month in The Lancet, has no explicit policy positions. But, by creating a holistic portrait of health around the world, it creates unrivaled evidence for how health has changed over time and what areas need the most attention. Health policy and funding from the WHO and many other organizations will focus on the areas of need outlined by the Global Burden of Disease.

"People are living longer, but they aren't healthier in their extra years."

When the project began twenty-two years ago, Dr. Christopher Murray, a physician and health economist, and Dr. Alan Lopez, an epidemiologist, set out to quantify human illness: Not only how many people died from liver failure but also how it that impacted their health while living. They could not simply compile existing studies that estimated the number of deaths from diseases because the total deaths in these single-disease studies far exceeded the actual number of people who died every year. Also, mortality data neither captured the impact of debilitating, but never fatal, ailments like lower back pain nor distinguished between the deaths of children and the elderly.

Working from government health data and demographic information, interviews and epidemiological research, Murray and Lopez created statistical models that measure absolute health lost -- imagine Nate Silver's FiveThirtyEight for causes of illness rather than political outcomes. In order to accurately show what diseases cause the most harm to total health, they put years of life lost due to premature death and the impact of living with illness or disability in comparable terms using a unit called the disability adjusted life-year (DALY). A DALY equals one year of life lost due to premature death. To quantify living with illness, values are assigned to represent the disability associated with hundreds of conditions. For instance, living with severe schizophrenia causes disability equivalent to three-quarters of a DALY but mild, chronic neck pain only causes one tenth of a DALY per year.

While the Global Burden of Disease for 1990 relied upon a panel of experts to assign the values to illnesses and disabilities, the Global Burden of Disease for 2010 drew on surveys of the public. In Peru, Bangladesh, Indonesia, Tanziania, and the United States, researchers surveyed low- and middle-income people at the household, and across the world, a similar number were surveyed online. A surveyed person would hear descriptions of two conditions -- such as mild alcohol abuse versus an amputated leg -- and pick the more palatable of the two. Researchers then used these preferences to generate the new set of values quantifying lost quality of life from a given illness. Many experts assumed that across cultures and socioeconomic status, people would have drastically different perceptions of the most disabling disabilities or illnesses -- a farmer valuing physical over mental health while more educated people fear intellectual impairment above all else. But, comparisons of the results from the five countries and online surveys found that peoples' attitudes towards a given condition maintained remarkable similarity. Regardless of the population's character, people value their health in the same ways.

In addition to the public opinion survey, the 2010 Global Burden of Disease dwarfs its predecessor in depth and rigor because of technological advancement and an influx of money.

In 2007, the Gates Foundation donated $105 million to the University of Washington -- the largest university gift ever for public health -- to establish the Institute of Health Metrics and Evaluation (IHME) to oversee this project. Murray became IHME's first director and with him came scores of full time researchers for this project. In addition to the increased size of research team, Dr. Ali Mokdad, Professor of Global Health at the University of Washington, explains that in 1990 "it used to take mainframe computers to do what laptops can do now." Modern computers allow much more sophisticated modeling of the complex interactions between risk factors and diseases around the world. The project has grown such that today's server farms still take days to compile all the demographic information, interviews, and historic and government health data.

For countries with limited or inaccurate registration of illness and death, Dr. Mokdad explained that researchers construct models of the nation's health based on any available information and the health of similar countries. Then, they repeatedly evaluate for accuracy by sampling the country's population and adjusting the model. Together, the newest models for Global Burden of Disease generate 615 million data points.

Presented by

Neal Emery is a Chicago-based writer who focuses on public health. He works for GlobeMed, a nonprofit that partners college students and community health organizations to complete public health projects.

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