Essay: Quality adjusted life years (QALYs) and disability adjusted life years (DALYs)

Quality adjusted life years (QALYs) and disability adjusted life years (DALYs) are both important measures used in healthcare studies. Both measures take into account time as well as some type of quality of burden to an individual’s life. While similar, when used in the correct context, both have different meanings and ways to calculate them.
Quality adjusted life years essentially quantify an individual’s disease burden over a specific length of time. Factors that play into the QALY calculation are perceived utilities (quality) and time. In the simplest form, the calculation presents as the utility multiplied by the number of years a person will be living with that utility (quality). Utilities can be measures on a scale from 0-1 with 1 representing perfect health and 0 representing death. For example, if a person with an unspecified disease state lived for 10 years with that disease at a quality of life of 0.7, their QALYs would be 7. There are three ways to capture the utility of a disease state: time-trade-off, standard gamble, and visual analogue scale. Visual analogue is usually the easiest to administer, but has limitations regarding at what point in care the patient is being asked. Standard gamble and time-trade-off are slightly more complicated to administer but can give a more accurate sense of the health state. Each has its strengths and weaknesses, and it’s up to study design and researcher preferences as to how they will calculate their utilities to use in the QALY equation.
Disability adjusted life years is another measure that describes disease burden. DALYs factor in a time component, life expectancy, and societies take on the disease burden. In a way, DALYs and QALYs are opposite in that DALYs will tell you how much life is lost and QALYs demonstrate how much life there is to live with a certain disease state. To calculate DALYs we combine morbidity and mortality. Mortality is the life expectancy of a healthy individual at the time they become ill minus the age of death. Morbidity is based on a diseases disability severity weight (Philip R. Lee Institute for Health Policy Studies, 2014). Because of the nature of this equation, researchers try to avert DALYs while gaining QALYs.
Both quality adjusted life year and disability adjusted life year measures are used in research and healthcare literature. They are especially used in pharmacoeconomic studies when trying to identify new treatments or procedures. Two specific studies that use these measures are Cost-Utility Analysis of the Cochlear Implant in Children using quality adjusted life years and Endovascular Therapy for Ischemic Stroke using disability adjusted life years.
Cost-Utility Analysis of the Cochlear Implant in Children is as it says, a cost-utility analysis with the aim at looking at the quality of life and cost attributed to children who receive a cochlear implant. This study is a good example of QALYs in literature because the main outcome measure is cost to society per QALY. It is also a good representation of QALYs because they used time-trade-off, visual analogue scales, and health utility index. The visual analogue scale was a simple 0-100 point scale with zero representing death and 100 representing perfect health in which the patient marked their perceived quality of life. In the time-trade-off model patients were given two alternatives: to stay deaf without a cochlear implant or a certain amount of time and to have perfect health for a certain amount of time that was shorter than the first option. The utility is then calculated by dividing the shorter amount of time by the larger amount of time (alternative 2 divided by alternative 1). The health utility instrument looks at domains of life from a patient survey and then maps them to utility score based on population based standard gamble. As for the life-year portion of the QALYs, the studied us a life expectancy table assuming life expectancy would not be altered with the addition of a cochlear implant. Using the cost-utility ration, the authors were able to calculate their final end point of cost to society per QALY. This study lays out their use of QALYs and data collected in a easy to follow, comprehensive manner making it a good example of using QALYs in healthcare literature.
Endovascular Therapy for Ischemic Stroke is an article that used disability adjusted life years. The purpose of this study was too quantify long-term patient benefits due to reduced delays in endovascular therapy for acute ischemic stroke. From the outcomes the researchers looked at, they were able to determine long-term disability translated into DALYs lost. Factors that played into the DALY calculation were distribution of patient demographics, general life expectancy, effect of mRS category on disability weight, effect of time on treatment effect of endovascular therapy, and effect of time on treatment effect of IV tPA. The DALY was not discounted or age-weighted follow WHO standard methodology. A DALY was calculated for each patient over their lifetime at the amount of treatment delay and then recalculated for the same patient if the treatment would have been given one minute earlier. As with the previous article, this article lays out in a comprehensive way how disability life years were calculated and used in terms of the final endpoints of the study.
While both quality adjusted life years and disability adjusted life years are useful in healthcare literature, they must both be used correctly to have a valid, strong study. Likewise, both have different aspects of them that make them more or less applicable to certain studies.
Disability adjusted life years are newer to literature and are largely debated. While it does measure disease burden, it might not take into account other comorbidities that can accompany the disease. For this reason, it can be difficult to accept the DALY as a complete considering many diseases have multiple comorbidities. Another way critics argue this point is by saying DALYs only take into account one specific disease state instead of a more complete health state (Gold, Stevenson, & Fryback, 2002). There is also concern about DALYs in terms of culture (Gold, Stevenson, & Fryback, 2002). Different cultures are able to take care of different disabilities better than others. In cultures that are better equipped to handle a disease state might have a lower disability score. DALYs work if you are applying that study to that specific culture, but the external validity might be limited.
Quality adjusted life years tend to have a better overall reputation in healthcare literature. Unlike DALYs, QALYs are often associated with a health state rather than a specific disease state (Gold, Stevenson, & Fryback, 2002). With this factor, some argue that they are able to capture more in relation to a person’s complete quality of life. Some do question the validity of using QALYs. QALYs look at different domains such as physical, psychological, symptoms, social, etc. Some argue that these different domains vary widely between people and that each describes a different view of health status. For this reason, having a bench mark QALY is difficult and it becomes hard to judge any QALY against another.
Both quality adjusted life years and disability adjusted life years have their advantages and disadvantages. Both must be used in perspective taking into account what factors play into each. QALYs and DALYs should both be understood by anyone in the healthcare field. Being able to understand how they are used and how they fit into a study is vital to implementing research into clinical practice. In the end, when used correctly, both are a comprehensive way of measuring how health can be affected and what effect that has on a person life.