This is lesson 3.3.2, Quality Adjusted Life Years. In this lesson we focus on deriving and calculating the quality adjusted life year, which can be used to measure the benefits of a technology. The quality adjusted life year, or QALY, combines morbidity and mortality into a single measure. Mortality is measured in terms of the life years or expected life years gained. Morbidity is measured by the quality of life that's associated with those extra years of life. The quality of life dimensions are weighted according to an individuals preferences measured in units often referred to as utility. A quality of life weight ranges between zero and one. Where zero is the quality of life associated with death, and one Is associated with perfect health. The quality is simply the calculation of the quality of life measure, times the number of years in a particular house state. And then the total benefit is the some of all qualities over time. This can be represented graphically which I'll show on the following slide. Consider the example of an 82 year old male who has a heart attack at the age of 85. At the age of 82, this individual has a quality of life of 0.95, that's close too but not perfect health. That health remains for the next three years, however at the age of 85 this person has a heart attack and then for the following two years, they have a quality of life of 0.75. Then, unfortunately, at the age of 87, this person passes away. Now, we can calculate the qualities associated with the treatment for a heart attack by calculating the sum that was described on the first slide. 3 years at 0.95 quality of life units + 2 years X 0.75 quality of life units = 4.35 total QALYs. Now we can assess how a new treatment for a heart attack either increases or decreases the total QALYs available to this person. Assume that the new treatment is offered to this person in year three when they have their heart attack. So again, this person starts at age 82 with 0.95 quality of life units. Then at age 85 this person has a heart attack, but instead of receiving the standard treatment they receive the new treatment and therefore they don't end at 0.75 quality of life units like they did before. Rather the treatment provides them with 0.85 quality of life units, and results in a longer amount of expected life years, and they end up living for a total of Four more years, out to here. So now we can calculate the total QALYs as 3 times 0.95, which is the same as before, but now, following the heart attack, it's four years times 0.85 ,85 units which is equal to 6.25 QALY's. The benefits of the new treatment for heart attack can then be calculated as the difference between the total QALY's for the new treatment minus. The total QALYs for the old treatment. The difference is 1.9 QALYs. In other words the new heart attack treatment results in an increase in 1.9 Quality Adjusted Life Years. There are a few more things to remember when using or calculating QALYs. First, it is important to remember that death has a quality of life rate of 0 in order to be able to combine morbidity and mortality. Now there are some who would argue that living with some diseases is worse than death. In this case, the quality of life weight would have a negative value and this complicates the calculations of QALYs. Second, the quality of life scale must have an interval property. This means that increase in quality of life from 0.3 to 0.4 but difference of One unit, or zero point one units, has the same meaning in terms of quality of life improvement as the difference between 0.7 to 0.8 also a difference of 0.1 units Now this may or may not be a strong assumption, depending on the technology that's being assessed. However, in order for the QALYs to be calculated in the way we described, this assumption must be made.