Not only lifespan. From the link you quote:

> Capacity for welfare = welfare range × lifespan. An individual’s welfare range is the difference between the best and worst welfare states the individual can realize.

> we rely on indirect measures even in humans: behavior, physiological changes, and verbal reports. We can observe behavior and physiological changes in nonhumans, but most of them aren’t verbal. So, we have to rely on other indirect proxies, piecing together an understanding from animals’ cognitive and affective traits or capabilities.

First time I see this "warfare range" notion and it seems quite clever to me.

Also the original article says 3.1% is the median while the mean is 19%. I guess that may be caused by individuals havûg différents experiences each other’s.