Before lecturing on quality adjusted life years (QALYs) you should carefully consider the most appropriate way to educate an audience.

The most obvious visual image related to QALYs is the graph of health utility over time. However, health economists called upon to give one-shot lectures to clinical audiences should not limit the visual images they employ to these standard graphs. The use of visual images relevant to clinicians’ day-to-day professional lives can facilitate communication.

Imagine discussing a series of syringes, flasks, and vats to illustrate the aggregation health-related quality of life over time and among individuals.

To begin illustrating the concept of measuring health related quality of life, you could ask members of a clinical audience to imagine filling a 10mL syringe in proportion to their personal feeling about health-related quality of life on the day of the lecture. When comparing different individuals, syringes filled with more liquid represent a higher quality of life for that individual.

To characterise health-related quality of life over a year, you might ask members of your audience to imagine filling a syringe each day. At the end of the year, the contents of all 365 syringes are emptied into a single flask that measures 3.65L of liquid when full.

The number of QALYs experienced by the individual in a year would be the fraction of the flask that is full. Many different sequences of syringe levels (i.e. daily quality of life) can yield the same total amount of liquid after a year.

The calculation of QALYs cannot distinguish among these sequences. The fact that the sequence of health-related quality of life experiences during a year does not affect the QALYs that are calculated is the key insight regarding aggregation over time for an individual.

Then, imagine a population of 100 individuals, each of whom has filled some fraction of a 3.65L flask. The QALYs experienced by the population (an important component of a cost-effectiveness analysis) can be measured by emptying all 3.65L flasks into a 365L vat.

The fraction of the vat that is full measures the average QALYs experienced. The key insight for aggregation at this stage is that the distribution of QALYs among members of the population is not considered.

An economist who wants to facilitate understanding of cost-effectiveness and QALYs should take advantage of the opportunity to be creative, or even light-hearted, when choosing visual images to use in a lecture. The images must meet two primary criteria: being appreciated by the audience and being easily explained by the economist.