The idea has obvious intuitive appeal: If you’re already sending community healthcare workers door-to-door in (say) remote parts of Sierra Leone to deliver routine childhood vaccines, why not have those healthcare workers deliver chlorine for disinfecting drinking water, or oral rehydration solution for treating dehydration from diarrhea?
After all, if you’re already spending money on the fixed costs of delivery, why not provide other programs at the same time? You’d be able to amortize the costs across multiple goods and offer additional benefits to the community. (If you’re getting groceries delivered, it’s more efficient to have one driver deliver your eggs and milk and vegetables all together than to have separate drivers going round delivering each one separately.)
GiveWell is very interested in these “layered interventions,” and we are excited to support them wherever they cross our cost-effectiveness threshold. But we’ve discovered it’s harder than you might think to find ways to combine programs effectively.