Hi, I'm Dr. Katrina Hauck, a health economist at the Imperial College London, School of Public Health. In this lecture, I will be introducing you to some of the different metrics we have for measuring health and the outcomes of interventions to improve health. We need to measure health because we need to understand health needs, track progress, and compare the health outcomes of different interventions. That's why health economists are so interested in this topic. I'll be talking about how we use these metrics to think about the impact of interventions on health. But they can of course also be used to think about the burden that diseases plays on populations. When measuring the impact of a disease or the impact of an intervention on a given disease, we can use a variety of different measures. We often use a count on natural unit measure such as infections averted, deaths averted, surgeries needed or cases prevented in the implementation of a given intervention. So, for example, how many malaria infections in children under five years of age occur each year? How many of those infections could be averted if insecticide treated bed nets were being used? If we need to compare health outcomes between two populations with different sizes, then we can use rates instead of counts. For example, consider two populations in the same area that are benefiting from different types of mosquito control interventions. Population A has 200 cases of malaria in a year, and population B has a 100 cases of malaria. But, A has a population of 10,000 and B has a population of 4,000. B has fewer cases over all, but more cases of malaria per person in the population. So, it might be that whatever mosquito control interventions are happening in population A are more effective than that in Population B. What we want to do is compare health outcomes between diseases. So, for example, what is the impact of tuberculosis compared to malaria on health over all? Or, what gives a greater health benefit? Distributing bed nets for malaria or screening populations for symptoms of tuberculosis? How can we compare the value of averting malaria infections to averting tuberculosis infections? Now, the case fatality rate of severe malaria in children is between seven percent and nine percent in many countries. For untreated tuberculosis, it is about 40 percent. Now, doesn't averted malaria case have the same value as an averted tuberculosis case? Clearly, we would be preventing more deaths if we avert tuberculosis cases rather than malaria cases. So, if we measured outcomes in terms of deaths rather than infections, this would at least allow us to compare across different interventions against malaria and tuberculosis. But then, we realize that malaria infections occur more often in children whereas tuberculosis affects all age groups. So, that means we are saving more life years if we avert a death from malaria compared to a death from tuberculosis simply because the average malaria death occurs to somebody with potentially more life ahead of them. The loss of life years at the age of five years is much higher than the loss of life years at the age of 50 years. If we were to measure these as the same, we would be underestimating the health impact of a disease which kills younger people more often. So, that leads us to the concept of years of life lost. This is calculated from the number of deaths multiplied by the life expectancy at the age at which a death occurs. Years of life lost is a really useful measure for understanding the impact of a disease and interventions to combat the disease on the health of a population. However, it only measures the impact of diseases resulting in death, but does not measure the impact of disease on the quality of a life before it causes death. For example, blindness, pain depression, and so on. For this, a measure of morbidity is required.