The standard view within effective altruism is that a person’s contribution to a particular focus area or intervention is determined by their *marginal impact*—that is, the impact that the contribution *adds* to the pre-existing impact.

The marginal impact should be clearly distinguished from the *average impact* of contributions to areas or interventions. If the marginal impact is *diminishing*—as it normally is—, the marginal impact is lower than the average impact, whereas if the marginal impact is *increasing*, the converse is true.

For instance, suppose that 1,000 people have contributed to a certain area, and that each of them have produced 10 expected units of value, but that the expected value of an additional person’s work is 5 units of value. Then the marginal expected impact of your work, which should determine your decision of whether you should work on the area, is 5 units of value. That is substantially lower than the average value of work on the area (including your work), which is close to 10 expected units of impact.

A corollary of the notion that you should try to maximize your marginal impact is that the area which is the highest *absolute priority*—i.e. which area should receive the most global resources—may not be the greatest *marginal priority*. If the absolute priority area is already heavily invested in, and if it exhibits diminishing marginal returns, other areas which are less heavily invested in may be higher marginal priority.

## Further reading

Library of Economics and Liberty. 2016. Margins and thinking at the margin.