Blood pressure (hypertension) is a major risk factor for many different medical conditions, including cardiovascular disease and kidney disease. It causes a systematic weakening of the heart muscle, making it work less efficiently and eventually terminating in cardiac arrest. The relationship between blood pressure and disease is log-linear. Blood pressure is affected by a multitude of external and internal factors, such as environment, nutrition and genetics, amount of fat tissue, alcohol use, smoking and physical activity, stress, and many others. It has been suspected that global trends in blood pressure have changed over time. NCD Risk Factor Collaboration, a network of medical scientists around the world, conducted a humongous study on blood pressure using data from 19.1 million individuals. They used systolic and diastolic blood pressure measurements and pooled data at the national, subnational, and community levels. Data from more than 200 countries were included in the study. The authors used a Markov chain Monte Carlo algorithm to fit the statistical model, taking errors, noise and different measurement devices into consideration. The major conclusion from this study is the shift of high blood pressure from high-income countries in North America and Europe to low-income countries in Asia and sub-Saharan Africa. Blood pressure has largely decreased in high-income countries – a trend also confirmed by other studies such as the MONICA project.