QALY is a metric used to rate health interventions and can be used for charity work also
It takes into account differences between how long would patient live and how enjoyable his live would be
It helps us to get more informed about different sacrifices we make when helping
How to compute
If we could extend someones life by 5 years with level of enjoyment of 7/10 then we would assign 3.5 QALY to that intervention
If we could extend someones enjoyment of the life to 90% over the period of 10 years then we would assign 9 QALY to that intervention
What if someone is going to die after 5 years with quality of life at 30% and by treatment we would increase his lifespan to 12 years with quality of life at 70%. Then the QALY for that intervention would be (0.7−0.3)∗5+0.7∗7=6.9.