The GiveWell Blog

Rethinking bednets

We granted Population Services International in our Saving Lives in Africa cause, focusing largely on their condom and bednet distribution and promotion programs. Soon after we cut the check, I got into a conversation with someone who questioned whether bednets are effective at all. He pointed me to a paper, “Combating malaria morbidity and mortality by reducing transmission,” which questions whether bednets are likely to have a long-term impact on malaria mortality.

Bednets reduce the number of bites that people receive from malaria-carrying mosquitoes, which in turn reduces incidence of malaria. This has two effects: (a) it reduces malaria mortality; but (b) it also reduces acquired immunity to malaria. The authors of this paper found, empirically, that areas that had lower rates of bites had similar rates of malaria mortality but a different age distribution of deaths. In places with high bite-rates, malaria mortality was restricted to children; in places with low bite-rates, adults died as well. The authors hypothesize that bednet programs may only shift the age at which people die from malaria, and have no impact on the total number of deaths from malaria.

This doesn’t mean bednets are useless. First of all, the analysis in the paper isn’t general enough to cover every case – there could be population configurations such that protecting people during their weakest years is a net benefit. There could be regions with high enough bite-rates that nets merely reduce the number of bites without affecting immunity. Also, even if total morbidity and mortality don’t change, there is definitely value in people living longer before they die. But, if it’s true that reducing mosquito bites can matter much less over the long term than over the short term, this is important when weighing the value of bednets. This paper really highlights what systematic analysis and measuring can do – and what you can miss by skimping on them.

At the moment, we’re still working on our education cause; bednets are something we’re thinking about, not devoting our time to. But if we revisit the cause of aid to Africa next year, we plan to incorporate this research into our analysis, and possibly change our recommendations. We don’t expect our decisions to be perfect; they’re merely our “best bet” given what we know. Enabling anyone to provide feedback on our grant decisions, which refines (or contradicts) our previous understanding, is precisely why we think a public discussion of what charities do and how well it works is necessary.


  • Carl Shulman on February 14, 2008 at 1:48 pm said:

    This is indeed very important for assessing the cost-effectiveness of bednets, although we should remember that if research into malaria vaccines is successful, then immunity may be acquired without infection.

  • Billy Acre on February 14, 2008 at 7:49 pm said:

    You have spelled “Population” incorrectly in the first line of this post, confirming in my mind that you do sloppy work.

  • Moon Over Jackson on February 16, 2008 at 11:20 pm said:

    Bednets, huh?

    What are you guys NOT experts on? Now you do epidemiology and public health as well as education policy? Amazing what an undergrad degree and a hedge fund education will do for you.

    Experts, heal thyselves.

    I find it hard to believe y’all are still trying to revive this completely bankrupt project.

  • Matt Stinson on February 19, 2008 at 2:57 pm said:

    I bet there are over 1.8million people/families today that could care less about what an acadmic paper has to say about the topic. In their real world, they are sleeping tonight with a bednet thanks to a great mission being executed by passionate and caring people –

    Note: I am not affiliated with Nothing But Nets but am familiar with their cause and work.

  • Dario Amodei on February 24, 2008 at 3:26 am said:

    This post initially made me reconsider my donations to bed net programs, but after looking more carefully through the literature, I am back to thinking bednets may be effective after all.

    The key point is that the Rogier and Trape 1996 paper relies entirely on indirect evidence–they look at age profiles of malaria incidence in areas with different transmission rates, and use that to guess at the likely long-term effects of bed nets. A more direct method would be to randomly divide a population of infants up into two groups, give bed nets to only one group, and then compare the malaria rates in the two groups over five or ten years. Several follow-ups to the Rogier and Trape paper have done approximately this (the control group was slightly different from what I described, due to ethical restrictions), and find that children who were protected by bed nets as infants aren’t any more likely to get malaria when they are older than children who weren’t. Here is a good summary of the evidence, with references to three of the studies.

    One caveat is that these studies only track malaria rates for 4 to 7.5 years, which might not be long enough for the full effects of delayed immunity to set in. Still, the new work casts serious doubt on the Rogier and Trape results.

  • michael vassar on February 25, 2008 at 11:20 am said:

    THANKS Dario!

  • Norma on March 22, 2008 at 6:25 pm said:

    I don’t know very many Americans who would be willing to have their children sleep under pesticide soaked bednets indefinitely. Do you know the long term effects? Gosh, people worry about fly paper strips.

  • Doug S. on March 25, 2008 at 12:29 am said:

    Whatever unknown effects the pesticide treated nets may have, they’re certainly a lot less bad than the known effects of getting malaria! 😉

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