SummaryInterventions to raise IQ could do a lot of good because of potentially significant flow-through effects of intelligence. IQ also has the benefit of being easily quantifiable, which would make it simpler to compare interventions.
Cost-effectiveness metricsAn important metric for comparing causes is cost-effectiveness (number of “things” accomplished per dollar). Which things should we count? Some cost-effectiveness measures are very specific, such as the number of malaria cases prevented per dollar. But when comparing between causes (such as between preventing malaria and improving education), it’s best to have a broad metric. There are two major types of metrics: health-related (e.g., quality-adjusted life years) and economic (e.g., increases in GDP). While health-related and economic metrics are appropriate in some cases, they aren’t ideal. Health-related metrics may be relatively unimportant if you care about far-future causes, such as existential risk. Economic outcomes can be hard to measure. Even GDP, one of the most common metrics of economic output, is not universally accepted as a valid measure of economic productivity.
Instead, I propose that effective altruists take a closer look at interventions to raise IQ. Cognitive improvements would have a wide range of benefits, described below, and would be easy to quantify. As Nick Beckstead argues, effective altruists who want to improve the far future should consider taking actions that have broad, generalized benefits.
Is the low end or the high end important?The most obvious way to measure cost-effectiveness of IQ interventions would be to measure the cost of increasing the average IQ in a population of a certain size by one point. However, the average hides a lot of information. Assume a population has an IQ distribution like this:
One intervention results in this:
Another results in this:
Same increase in the average, very different impacts.
It’s an open question whether it’s more important to improve IQ at the low end or the high end. (The two often aren’t mutually exclusive.) My intuitions:
- To reduce violence, it would be most important to improve IQ at the low end.
- Better decision-making would occur more dramatically at the low end, but people at the high end are more likely to be making important decisions.
- Improving the low end would be important for increasing economic productivity, but most long-term growth would come from the high end (due to increased technological progress).
- Most of the benefits from innovation would come from the high end.
Benefits of increasing IQ
Decreased violenceThe strong correlation between low IQ and violent or criminal behavior is clear from extensive research.    The fact that the correlation is observed even among children raised by the same parents suggest that IQ causes violent behavior, rather than some environmental factor causing both low IQ and violence. 
Steven Pinker argues that the Flynn effect (the consistent increase in IQ that has been observed over generations for about a century) is responsible for the remarkable decrease in violence that has occurred from prehistoric times to the present day. According to him, reason and rationality are some of the “better angels of our nature” that can curb violence. It is plausible that increased IQ will lead to better reasoning, though uncertain. (See below.)
There is good evidence that the sharp drop in crime during the latter half of the twentieth century was due to decreased exposure to lead. (See here.) One of the most notable effects of lead exposure is decreased IQ, but it’s unclear whether the increase in crime associated with lead exposure is due to its cognitive effects.
Increased economic productivityA 1-point increase in IQ corresponds to approximately a 1% increase in wages for an individual. There is also a strong correlation (0.82) between IQ and per capita GDP, though it seems plausible that causality runs in both directions, with extreme poverty causing low IQ. 
Improved decision-makingA study of college students showed that students with higher IQ did not do significantly better on some tests of rationality, though they did do better on other tests and were better able to evaluate the quality of an argument. People with high IQ are also more likely to underestimate their own biases that hinder their rationality.
However, the average college student probably has an IQ far above the global average, so the low end was not represented in this study. It also did not capture the high end, since it only included students from an average college. Additionally, it only measured abstract tests of irrationality (such as the base rate fallacy). There are plenty of more prosaic examples of rationality in everyday life. (Since rationality has connotations of abstract reasoning, I prefer to call this “decision-making”.) It’s unclear that the formal study of fallacies and biases significantly affects decision-making. (See here and here.) On more mundane matters, someone with a low IQ would be expected to make worse decisions than someone with an average IQ. People with low IQs are more likely to experience a range of poor outcomes, such as teen pregnancy, controlling for childhood socioeconomic status.
I did not find any research on whether IQ affects rationality at the high end, but it seems like a promising topic, since high-IQ people are more likely to be making important decisions in society.
In a survey that controlled for factors such as education and income, IQ was correlated with opposition to economic protectionism. Economists almost universally agree that protectionism is bad policy. Even Paul Krugman, who generally favors greater government intervention in the economy, opposes protectionism. (He once said that if there were an Economist’s Creed, it would include the statement “I advocate free trade.”) Free trade is a particularly worthy cause for effective altruists, who care about the interests of people in the developing world. It is estimated that the removal of all subsidies and trade barriers would have a net economic benefit of $44 trillion, much of which would benefit the poor. Since there’s currently widespread public support for protectionism, it seems plausible that increased opposition could lead to the removal of trade barriers.
InnovationIncreasing IQ could have large benefits in scientific and technological progress. People with extremely high intelligence are far more likely than average people to receive tenure at a research university and be successful in business. Even within scientific research, the most influential research tends to be produced by people who have higher intelligence than the average scientist.
Interventions to increase IQSocial interventions targeting young children may be able to increase intelligence. The Home Observation for Measurement of the Environment (HOME) is an inventory that measures the quality of a child’s home environment, with items such as “child has three or more puzzles” and “parent holds child close for 10-15 minutes per day”. Controlling for maternal IQ, the HOME score was positively correlated with IQ for two-year-olds. However, interventions to change behavior are often difficult to implement, though there are some that have been successful.
Nutrient supplements (particularly iodine, but also protein and iron) are a cost-effective way to increase IQ. Studies generally only report changes in the median or the mean IQ, but presumably supplements would mainly help the low end of the spectrum.
Another option is to use in vitro fertilization to increase IQ, but this could be politically controversial.
Implications for effective altruistsEffective altruists may give more consideration to causes such as iodine supplementation because of their large flow-through effects compared to other public health programs, such as deworming. While this would be a step in the right direction, I generally think it’s relatively ineffective to fund proven, non-controversial public health interventions, because the market for funding these causes is fairly saturated. Instead, I propose that effective altruists support efforts to do research into IQ. This could mean doing the research directly or doing funding or advocacy. In general, effective altruists should support research if they have reason to believe it’s systematically underfunded.
Which types of research are underfunded?
- Social interventions? While psychologists are aware of some social factors that influence cognitive abilities, it seems that the main bottleneck is the difficulty in changing behavior through social interventions. Given the large number of people working on social interventions of all types, I don’t believe this would be systematically underfunded. (On the other hand, my impression is that social psychology and public policy are seen as lower-status than, say, theoretical physics, so they may attract fewer talented people. This would imply that there are opportunities for a bright person to have an impact.)
- Biomedical interventions? There is a lot of research into interventions such as iodine supplementation that raise IQ. However, I believe that these may be underfunded because they are viewed as public health interventions and the long-term benefits are not appreciated. I think working to identify new biomedical influences on IQ would be very cost-effective.
- Genetic interventions? This type of research is probably the most underfunded, due to social stigma. However, the main bottleneck may be changing public attitudes regarding these efforts, which brings us back to the realm of social psychology and advocacy.
- Childhood IQ tests are inaccurate, so it can take decades to evaluate a new intervention. Response: Though childhood IQ tests are less accurate than adult tests, they correlate fairly well with adult scores. The question is not whether IQ is easy to measure, but whether it’s easier than other metrics of success, such as “spreading positive values”. Additionally, this implies that it may be worth investing in better tests of IQ.
- Other interventions, such as deworming, have similar flow-through effects. Response: There is some evidence (summarized here) that deworming increases school attendance, wages, and labor productivity (though not through increasing IQ). However, the evidence is mixed and there’s a much narrower range of benefits than raising IQ could have. Additionally, school attendance seems like a bad metric of success, given the extremely poor quality of schools in the developing world.
- We might create evil geniuses. Response: This seems worth exploring further. However, the preliminary evidence suggests that raising IQ will reduce violence. I don’t currently advocate the creation of superhuman intelligence, simply increasing intelligence within the “normal” range. If one thinks that increasing the number of people in the (normal) high-IQ range would be net negative, would it be good to reduce the number of people in this range? If one says it wouldn’t be good, there’s an appearance of status quo bias.
Thanks to Jonah Sinick for research.