Fig. 1
From: Economic evaluation: a reader’s guide to studies of cost-effectiveness
How utilities are tallied up to calculate QALYs. 1a & 1b: QALYs are calculated 2 dimensionally, using an ‘area under the curve’ method, so 1 year at full health is 1 QALY, and 2 years at utility of 0.5 is also 1 QALY. 1c illustrates the ‘area under the curve’ in a hypothetical study that followed people until death, with interim follow-up data collection points at 1, 5, and 8 years. We see that the control group experienced 3.95 QALYs and the treatment group experienced 5.95 QALYs, so the QALY gain from treatment (the area in green) is approximately 2.0 QALYs