Hi Flemming, you’re right that high survivorship would generally entail a long life expectancy. Sorry, this summary didn’t adequately explain how “RWE” is to be calculated. In the RWE calculation, welfare expectancy is normalized around the average annual welfare across all the ages within an individual’s maximum lifespan (i.e. the lifespan they might live if all their needs were met and they died of old age), so the average age-specific welfare == 1. This normalized welfare expectancy is then divided by the life expectancy, which always values every year of life as 1. This controls for differences in life expectancy, so in the pre-print linked above, species with life expectancies as different as 1 year and 40 years come out with RWE values pretty near 1 on either side.
RWE is intended to show whether the ages which most individuals live through are especially good or especially bad ones. For example, as kcudding pointed out in an earlier comment, some herbivorous insects seem like they may have higher welfare as juveniles than as adults. This would lead to RWE > 1. For many species, though, the juvenile period involves very high mortality, so most individuals only survive to experience desperate times. They would probably end up with RWE < 1. RWE always tends towards 1 as life expectancy increases towards the maximum lifespan, including in humans (which I can say with confidence since we have actual data on age-specific psychological wellbeing for humans!), which emphasises that it is about identifying a gap between welfare expectancy and life expectancy, not a welfare metric in itself.
I think this would be way easier to understand with an equation or two. Let w be overall lifetime wellbeing, let wt be age-specific wellbeing at time t, let L be lifetime and let us denote averages over lifetime by an overbar. If so, it seems like the “normalized age-specific wellfare” is wt,norm=wt/¯w. It is not clear what “this normalized welfare expectancy” refers to, since it can either mean wt,norm or wnorm=∑twt,norm (I assume here that overall wellbeing is the sum of age-specific wellbeing). Thus, the RWE is calculated as follows:
I find both of these formulas to be rather strange, and devoid of a rationale. Have I misunderstood you?