Why would being under a bednet reduce fertility? Two things that could make sense:
(1) The authorsā hypothesis of a mere timing shift, as fertility temporarily increases as a result of better health, followed by a (presumably similarly temporary) compensatory reduction in the immediately subsequent years, perhaps from the new parents stabilizing on their preferred family size. As noted, this hypothesis does not imply reduced total fertility.
(2) If some families stabilize on their preferred family size by (eventually) having an extra baby in the event that a previous one dies tragically early, then fertility (total births) could be expected to drop slightly as a result of life-saving interventions, but not to the point of exceeding the number of lives saved (or reducing total population).
In the absence of a plausible explanation that should lead us to view the outcome in question as especially likely, randomly positing a systematic negative population effect seems unreasonable to me. Anything is possible, of course. But selectively raising unsupported possibilities to salience just to challenge others to rule them out is a bad way to approach longtermist analysis, in my view. (Basically, the slight risk of negative fertility effects is outweighed by the expected gain in population, but common habits of thought overweight salient ārisksā in a way that makes this dialectical method especially distorting.) See also: Itās Not Wise to be Clueless.
In places where lifetime births/āwoman has been converging to 2 or lower, saving one childās life should lead parents to avert a birth they would otherwise have. The impact of mortality drops on fertility will be nearly 1:1, so population growth will hardly change. In the increasingly exceptional locales where couples appear not to limit fertility much, such as Niger and Mali, the impact of saving a life on total births will be smaller, and may come about mainly through the biological channel of lactational amenorrhea. Here, mortality-drop-fertility-drop ratios of 1:0.5 and 1:0.33 appear more plausible.
So it looks like saving lives in low income countries decreases fertility, but still increases population size. Because of the decrease in fertility, it may be good to downgrade the cost-effectiveness. The above would suggest multiplying it by around 0.5 (= 1 ā 0.5) to 0.7 (= 1 ā 0.33).
Yeah, thatās more in line with what I would expect. (Except the first sentence may be a bit hasty. Many first-world couples delay parenting until their 30s. If a child dies, they may not be able to have anotherāesp. since a significant period of grieving may be necessary before they were even willing to.)
Why would being under a bednet reduce fertility? Two things that could make sense:
(1) The authorsā hypothesis of a mere timing shift, as fertility temporarily increases as a result of better health, followed by a (presumably similarly temporary) compensatory reduction in the immediately subsequent years, perhaps from the new parents stabilizing on their preferred family size. As noted, this hypothesis does not imply reduced total fertility.
(2) If some families stabilize on their preferred family size by (eventually) having an extra baby in the event that a previous one dies tragically early, then fertility (total births) could be expected to drop slightly as a result of life-saving interventions, but not to the point of exceeding the number of lives saved (or reducing total population).
In the absence of a plausible explanation that should lead us to view the outcome in question as especially likely, randomly positing a systematic negative population effect seems unreasonable to me. Anything is possible, of course. But selectively raising unsupported possibilities to salience just to challenge others to rule them out is a bad way to approach longtermist analysis, in my view. (Basically, the slight risk of negative fertility effects is outweighed by the expected gain in population, but common habits of thought overweight salient ārisksā in a way that makes this dialectical method especially distorting.) See also: Itās Not Wise to be Clueless.
From the abstract of David Roodmanās paper on The Impact of Life-Saving Interventions on Fertility:
So it looks like saving lives in low income countries decreases fertility, but still increases population size. Because of the decrease in fertility, it may be good to downgrade the cost-effectiveness. The above would suggest multiplying it by around 0.5 (= 1 ā 0.5) to 0.7 (= 1 ā 0.33).
Yeah, thatās more in line with what I would expect. (Except the first sentence may be a bit hasty. Many first-world couples delay parenting until their 30s. If a child dies, they may not be able to have anotherāesp. since a significant period of grieving may be necessary before they were even willing to.)