= Incremental cost-effectiveness ratio
{title2=$\operatorname{ICER}=\Delta C/\Delta E$}
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= ICER
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The <incremental cost-effectiveness ratio> divides an intervention's additional mean cost by its additional mean effect relative to a comparator. Its units are cost per outcome unit. When both increments are positive, comparison with a threshold $\lambda$ is equivalent to checking whether the <incremental net monetary benefit> $\lambda\Delta E-\Delta C$ is positive. When $\Delta E<0$ the inequality reverses on division, and when $\Delta E=0$ the ratio is undefined. A ratio alone cannot identify the quadrant of the <cost-effectiveness plane>.
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