There are a few different definitions of neglectedness. For example, consider the following three:
“If we add more resources to the cause, we can expect more promising interventions to be carried out.” (source (h ps://80000hours.org/2013/12/a-framework-for-strategically- selecting-a-cause/))
You care about a cause much more than the rest of society. (source (h ps://80000hours.org/2014/01/neglectedness-and-impact/))
“How many people, or dollars, are currently being dedicated to solving the problem?” (source (h ps://80000hours.org/articles/problem-framework/#definition-2))
The first one is quite close to expected value-type calculations and so it is quite clear why it is important. The second and third are more concrete and easier to measure but ultimately only relevant because they are proxies of the first (h ps://80000hours.org/articles/problem- framework/#why-is-it-important). If society is already investing a lot into a cause, then the most promising interventions in that cause area are already taken up and only less effective ones remain.
Because the second and, even more so, the third are easier to measure, I expect that, in practice, most people use these two when they evaluate neglectedness. Incidentally, these definitions also fit the terms “neglectedness” and “crowdedness” much be er. I will argue that neglectedness in the second and third sense has to be translated into neglectedness into the first sense and that this translation is difficult. Specifically, I will argue that the diminishing returns curves (h ps://en.wikipedia.org/wiki/Diminishing_returns) on which the connection between already invested resources and the value of the marginal dollar is based on can assume different scales and shapes that have to be taken into account.
Caspar Oesterheld, Complications in evaluating neglectedness, The Universe From an Intentional Stance, June 25, 2020