First of all, there's good news for much of the world's population:

On average, you are more likely to live longer than your ancestors.

Life expectancy is rising even in some of the world's poorest countries, according to a new study by the University of Washington's Institute for Health Metric and Evaluation (IHME). Within 23 years, from 1990 until 2013, life expectancy for both men and women rose 6.2 years, from 65.3 to 71.5.

Estimations of life expectancy are frequently thrown around to make all kinds of arguments: Politicians use them to advocate health-care systems, opponents of the tobacco industry tell you how much each cigarette shortens your life, and yoga teachers refer to them to explain how much longer meditation will help you live.

But what if life expectancy isn't the actual unit we should measure?

IHME suggests an alternative measurement: counting the years you will spend living free of disease and disability on average. When the researchers calculated the world's average life expectancy per country and compared them to the average years lived being healthy, they were surprised: Despite the fact that people around the world are living longer, they are also expected to spend more time suffering from diseases and other conditions. This interactive charts allows you to compare countries.

Although life expectancy increased on average, the rates in some countries stagnated.  "The increase in healthy life expectancy has not been as dramatic as the growth of life expectancy, and as a result, people are living more years with illness and disability," the study's authors explained.

The researchers used the concept of HALE, which measures healthy life expectancy at birth and takes into account "nonfatal conditions and summarizes years lived with disability and years lost due to premature mortality."

Health loss was primarily associated with "heart disease, lower respiratory infections, stroke, low back and neck pain." Men are more at risk of suffering road injuries, while women are disproportionately affected by psychological disorders.

What is particularly striking is that in some countries, such as Botswana, Belize and Syria, healthy life expectancy stagnated or even dropped, as was also the case in South Africa, Paraguay, Belarus, Lesotho and Swaziland.

People in countries such as Nicaragua and Cambodia have experienced dramatic increases in healthy life expectancy since 1990, 14.7 years and 13.9 years, respectively. The reverse was true for people in Botswana and Belize, which saw declines of two years and 1.3 years, respectively.

Why is there so much variation? 

Reasons why people get sick around the world differ, of course. However, the University of Washington researchers said several factors played a disproportionately big role, including "per capita income, population age, fertility rates, and years of schooling."

These factors alone can explain more than half of the cross-country variation, according to the study. Although those factors can be used to predict differences regarding maternal disorders, they do not apply in cases of cardiovascular diseases and diabetes. In the latter cases, access to health-care systems, diets or average working hours could provide further insights.

Will the average time spent in health catch up with life expectancies? 

Health has improved significantly around the world, "thanks to marked declines in death and illness caused by HIV/AIDS and malaria in the past decade and significant advances made in addressing communicable, maternal, neonatal, and nutritional disorders," the study's authors concluded.

However, as the following chart shows, the gap between average life expectancy and years spent without illness or disability continues to grow.

So, what's the study's lesson for the future? "The challenge is to invest in finding more effective ways of preventing or treating the major causes of illness and disability," professor Theo Vos of IHME was quoted as saying in a publication released by the university.

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