For an atomic intervention, the relevant scale is the amount of good that can be done by a given amount of money, the relevant tractability is whether there is good evidence that the intervention works, and the relevant neglectedness is room for more funding. (This is the GiveWell framework.)
For a systemic intervention, the relevant scale is the amount of good that can be done by solving the problem, the relevant tractability is how much of the problem would be solved (in expectation) by increasing the resources going towards it by X%, and the relevant neglectedness is the amount of resources it would take to increase by X% the amount of resources devoted to the problem. (If there are increasing marginal returns or diminishing marginal returns, then X should be chosen based on the amount that the prospective donor/prospective employee would increase resources. If there are constant marginal returns, X can be set based on what would make it easier to predict how much of a problem would be solved (e.g. choosing a 50% increase even though your donation would only amount to a 0.1% increase because it’s easier to get a sense of how much of a problem would be solved by a 50% increase). (This is the 80,000 Hours framework.)
When EAs discuss scale, they generally mean scale in the sense that the term is used for systemic interventions (i.e. the scale of the problem, not the scale of the good the intervention would do). When EAs discuss tractability, they generally mean tractability in the sense that the term is used for atomic interventions (i.e. whether the intervention would be successful, not how much of the problem it would solve in expectation). EAs should avoid mixing and matching scale and tractability in this way.
See my previous comment here for a lengthier discussion of this issue.
For an atomic intervention, the relevant scale is the amount of good that can be done by a given amount of money, the relevant tractability is whether there is good evidence that the intervention works, and the relevant neglectedness is room for more funding. (This is the GiveWell framework.)
For a systemic intervention, the relevant scale is the amount of good that can be done by solving the problem, the relevant tractability is how much of the problem would be solved (in expectation) by increasing the resources going towards it by X%, and the relevant neglectedness is the amount of resources it would take to increase by X% the amount of resources devoted to the problem. (If there are increasing marginal returns or diminishing marginal returns, then X should be chosen based on the amount that the prospective donor/prospective employee would increase resources. If there are constant marginal returns, X can be set based on what would make it easier to predict how much of a problem would be solved (e.g. choosing a 50% increase even though your donation would only amount to a 0.1% increase because it’s easier to get a sense of how much of a problem would be solved by a 50% increase). (This is the 80,000 Hours framework.)
When EAs discuss scale, they generally mean scale in the sense that the term is used for systemic interventions (i.e. the scale of the problem, not the scale of the good the intervention would do). When EAs discuss tractability, they generally mean tractability in the sense that the term is used for atomic interventions (i.e. whether the intervention would be successful, not how much of the problem it would solve in expectation). EAs should avoid mixing and matching scale and tractability in this way.
See my previous comment here for a lengthier discussion of this issue.