The idea behind Copenhagen Consensus 2012 is to prioritize some of the world’s most important spending, with the latest economic analysis providing us with an input. In a series of articles, I am drawing on new research papers that present the costs and benefits of the smartest ways to respond to global challenges. Each article has a poll, and Slate readers can vote on the investments that they believe should be the highest priorities—along with those that should not. You can read more about the rationale behind the project here.

Over the course of the series, we will see how readers rank responses to a range of challenges, and at the end we will identify the investments that Slate readers think should be the highest priority. We will be able to contrast these with the findings of a panel of Nobel laureate economists.

Yesterday we looked at new research by economists looking at different ways to respond to the major killer: infectious diseases. Some commenters discussed whether water and sanitation problems were the real problem. While sanitation investment wouldn’t directly reduce the death-toll of the diseases we discussed yesterday, it is a priority, and today’s article summarizes new research on this topic.

On this article and on an earlier piece in the series, several readers have discussed the use of DDT, the insecticide used to kill mosquitos and a one-time mainstay of the fight against malaria. DDT is, of course, highly controversial because of its environmental impact and is banned in the United States and many countries. Some studies have shown that its banning led to an increase in the incidence of malaria. However, its negative environmental impacts were mainly in large-scale use for agricultural spraying, whereas its use for indoor spraying (killing the mosquitos for months) or for bed-nets only use minute amounts with minimal environmental impact and large health benefits.

After three topics—malnutrition, chronic disease, and infectious disease —we can see how Slate readers have prioritized the investments. Remember, we asked you which options you thought policymakers should put first. (And remember: You can go back and vote in the various polls today; we’ll be finalizing the Slate readers’ list at the end of the series).

As you can see, the latest investment opportunities—those to fight infectious disease—fit in without strongly upsetting the front-runners (or those that Slate readers really didn’t like, such as the salt reduction campaign!).

In addition to the fact that the top-ranked priorities all have low costs and relatively high benefits in economic terms, we can see another theme emerging: Other than tobacco taxation, the top five-ranked options would all directly impact child health (and tobacco taxation would obviously help, as well).

It is interesting to note that investment in an HIV vaccine—which, if successful, could dramatically and comprehensively transform the fight against the killer disease—was given the lowest-ranking among the infectious disease responses. Perhaps this is because Slate readers feel that this—along with the lowest-ranked option of crop advisory text messages—should be the domain of private business, rather than policy makers and philanthropists.