The GiveWell Blog

Why we don’t use subnational malaria mortality estimates in our cost-effectiveness models

Summary

We recently completed a small project to determine whether using subnational baseline malaria mortality estimates would make a difference to our estimates of the cost-effectiveness of two of our top charities, the Against Malaria Foundation and Malaria Consortium. We ultimately decided not to include these adjustments because they added complexity to our models and would require frequent updating, while only making a small difference (a 3-4% improvement) to our bottom line.

Though this post is on a fairly narrow topic, we believe this example illustrates the principles we use to make decisions about what to include in our cost-effectiveness model.

Background

Two of our top charities—the Against Malaria Foundation (AMF) and Malaria Consortium’s seasonal malaria chemoprevention program—implement programs to prevent malaria, a leading killer of people in low- and middle-income countries.

One of the core reasons we recommend AMF and Malaria Consortium is their cost-effectiveness: how much impact they have (e.g., cases of malaria prevented, malaria deaths averted) with the funds they receive. Our estimates of charities’ cost-effectiveness isn’t just helpful to us in determining which charities should be GiveWell top charities; we also rely on these estimates to guide our decisions about how to allocate funding between our top charities.

Our cost-effectiveness estimates for AMF and Malaria Consortium use country-wide data on malaria mortality and malaria incidence in the places that both organizations work.1In both cases, we rely on reports by Cochrane, an organization that produces systematic reviews and other synthesized research to inform decision-makers. For AMF, we use a decline in all-cause mortality, because the Cochrane review of anti-malarial bed net distributions reports the effect in terms of a reduction in all-cause mortality. For Malaria Consortium, we use a decline in malaria mortality (proxied by a decline in malaria incidence), as the Cochrane review of seasonal malaria chemoprevention reports the effect in terms of a reduction in malaria incidence, but not all-cause mortality. See our cost-effectiveness analysis for more details. However, neither organization serves a whole country—rather, they operate in sub-national regions—so the use of country-level estimates could cause us to either underestimate or overestimate their cost-effectiveness. If, for example, these programs are focused in the areas of the country with the highest malaria burden, using the average burden for the country would lead us to underestimate their cost-effectiveness. So, we completed a project to determine how much of an impact using subnational estimates would have, to consider whether we ought to incorporate this information into our cost-effectiveness analysis.

How we estimated the impact of subnational malaria incidence

AMF distributes insecticide-treated nets to prevent malaria; Malaria Consortium’s seasonal malaria chemoprevention (SMC) program provides preventive anti-malarial drugs. We used estimates of subnational malaria incidence from the Malaria Atlas Project (MAP) to see if regions covered by nets or eligible for SMC had higher or lower incidence than the average in the country in which they are located.2We assume that the regional distribution of malaria incidence is a reasonable proxy for the regional distribution of malaria mortality.

We focused on all areas covered by nets or eligible for SMC (rather than those covered by our top charities, specifically) for two reasons:

  1. Our understanding is that when our top charities contribute resources to a country’s net distribution or SMC programs, the marginal region covered by these additional resources is not necessarily the same as the region to which these resources are assigned (because these resources are fungible with other resources within the national programs).3A limitation of this analysis is it does not account for the possibility that AMF and Malaria Consortium are causing locations that are higher priority or lower priority than the average location already covered by nets or eligible for SMC to be covered on the margin. We do not explicitly include estimates of the marginal region funded in our cost-effectiveness analysis because we often have limited information about which regions would be covered with marginal additional funds.
  2. Our aim is to estimate the cost-effectiveness of funds donated to these organizations in the future. The subnational region where AMF has worked in the past has not historically been a good indicator of the region where it will work in future.

Results for net distributions in countries where AMF works

We looked at geographical variation in malaria incidence in countries where AMF works, weighting each region by the number of nets it currently receives.4We assume that where nets have been delivered in the past is a good proxy for where new nets will be delivered in the future. The data and calculations are in this spreadsheet.

The average net delivered in the countries in which AMF works is hung in an area with 0-9% higher malaria incidence than the average in that country, and the weighted average adjustment to AMF’s cost-effectiveness would be 3% (in other words, AMF becomes 3% more cost-effective if we incorporate subnational estimates).5See Cell J114. We did not include Papua New Guinea (where AMF funds some nets) in this analysis, as MAP only covers countries in Africa.

Country Adjustment
Zambia +9%
Uganda +4%
Ghana +4%
Democratic Republic of the Congo +1%
Togo +1%
Malawi +0%

Results for SMC in countries where Malaria Consortium works

We looked at six countries comprising >95% of Malaria Consortium’s SMC spending and compared malaria incidence in districts eligible for SMC with the country-wide average.6“The suitability of an area for SMC is determined by the seasonal pattern of rainfall, malaria transmission and the burden of malaria. SMC is recommended for deployment in areas: (i) where more than 60% of the annual incidence of malaria occurs within 4 months (ii) where there are measures of disease burden consistent with a high burden of malaria in children (incidence ≥ 10 cases of malaria among every 100 children during the transmission season) (iii) where SP and AQ [the drugs used to treat children] retain their antimalarial efficacy.” WHO SMC field guide (2013), Pg 8.7The data and calculations are in this spreadsheet.

The average region eligible for SMC in countries where Malaria Consortium works has -2% to 17% higher malaria incidence than the average in that country. The weighted average adjustment to Malaria Consortium’s cost-effectiveness would be 4%.8See Cell C126.

Country Adjustment Commentary
Guinea +17% Conakry, the capital, is ineligible for SMC and has low incidence.
Nigeria +12% SMC appears to be targeted in the north, where malaria incidence is slightly higher.
Niger +2% The majority of the population is either covered or planned to be covered from 2019.
Burkina Faso 0% All districts are eligible.
Mali 0% All districts are eligible.
Chad -2% The four regions with very low malaria incidence (Borkou, Tibesti, Ennedi Est and Ouest) aren’t eligible for SMC, but are sparsely populated.

What we concluded

We decided not to include these adjustments in our cost-effectiveness analysis because they increased complexity, without substantially affecting the bottom line.

When we decide whether to include adjustments in our model in general, we use a framework that first takes our best guess of the likely effect size and then rates each of the remaining question on a three-point scale.

Score9We use these scores as a qualitative guide to help us think through what to include in our cost-effectiveness analysis. You can see the rubric we use to assign scores in this spreadsheet. Commentary
Best guess of effect size 3-4%
Can it be objectively justified? 3/3 While we have not investigated the MAP data in detail, we would guess that after further investigation, we would conclude it provides a reasonable approximation of subnational malaria incidence.10You can read more about MAP’s methodology in this paper.
How easily can it be modelled? 3/3 The methodology is clear and simple.
Is it consistent with our other cost-effectiveness analyses? 2/3 We could include subnational adjustments for both of our top charities that implement malaria-prevention programs, but we believe it is unlikely there would be sufficient data to do the same for prevalence of worms or vitamin A deficiency (the focus of five of our other seven top charities).

Even though these adjustments can be objectively justified and are fairly easy to model, the bottom-line difference they make to our cost-effectiveness estimates is insufficient to warrant the (moderate) increase in the complexity of our models. These adjustments would also introduce an inconsistency between our methodologies for top charities. As a result, we are not planning to incorporate subnational adjustments at this time.

When would we revisit this conclusion?

We will revisit using subnational malaria mortality estimates if AMF or Malaria Consortium start working in countries where it would make a large difference to the bottom line. We would include subnational adjustments if AMF contributed nets in any of these countries: Djibouti (+500% adjustment), South Africa (+259%), and Swaziland (+126%), where malaria is endemic in some parts of the country but not others. We would also consider subnational adjustments if AMF contributed nets in Namibia (+25%), Kenya (+23%), Madagascar (+14%), or Rwanda (+10%).11The data and calculations are in this spreadsheet.

We will investigate whether subnational adjustments would make a substantial difference if Malaria Consortium enters additional countries; at this time, we do not have details on which regions are eligible for SMC in countries in which Malaria Consortium is not currently operating.12We have not yet prioritized getting details on which regions are eligible for SMC in countries in which Malaria Consortium does not currently work, as this would likely impose a substantial time cost on Malaria Consortium.

You can read the internal emails discussing our decision process here.

Notes   [ + ]

1. In both cases, we rely on reports by Cochrane, an organization that produces systematic reviews and other synthesized research to inform decision-makers. For AMF, we use a decline in all-cause mortality, because the Cochrane review of anti-malarial bed net distributions reports the effect in terms of a reduction in all-cause mortality. For Malaria Consortium, we use a decline in malaria mortality (proxied by a decline in malaria incidence), as the Cochrane review of seasonal malaria chemoprevention reports the effect in terms of a reduction in malaria incidence, but not all-cause mortality. See our cost-effectiveness analysis for more details.
2. We assume that the regional distribution of malaria incidence is a reasonable proxy for the regional distribution of malaria mortality.
3. A limitation of this analysis is it does not account for the possibility that AMF and Malaria Consortium are causing locations that are higher priority or lower priority than the average location already covered by nets or eligible for SMC to be covered on the margin. We do not explicitly include estimates of the marginal region funded in our cost-effectiveness analysis because we often have limited information about which regions would be covered with marginal additional funds.
4. We assume that where nets have been delivered in the past is a good proxy for where new nets will be delivered in the future. The data and calculations are in this spreadsheet.
5. See Cell J114. We did not include Papua New Guinea (where AMF funds some nets) in this analysis, as MAP only covers countries in Africa.
6. “The suitability of an area for SMC is determined by the seasonal pattern of rainfall, malaria transmission and the burden of malaria. SMC is recommended for deployment in areas: (i) where more than 60% of the annual incidence of malaria occurs within 4 months (ii) where there are measures of disease burden consistent with a high burden of malaria in children (incidence ≥ 10 cases of malaria among every 100 children during the transmission season) (iii) where SP and AQ [the drugs used to treat children] retain their antimalarial efficacy.” WHO SMC field guide (2013), Pg 8.
7, 11. The data and calculations are in this spreadsheet.
8. See Cell C126.
9. We use these scores as a qualitative guide to help us think through what to include in our cost-effectiveness analysis. You can see the rubric we use to assign scores in this spreadsheet.
10. You can read more about MAP’s methodology in this paper.
12. We have not yet prioritized getting details on which regions are eligible for SMC in countries in which Malaria Consortium does not currently work, as this would likely impose a substantial time cost on Malaria Consortium.

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