In August the Woodrow Wilson School's Anne Case, Professor of Economics and Public Affairs and director of the Research Program in Development Studies, and Christina Paxson, Professor of Economics and Public Affairs and director of the Center for Health and Wellbeing, released a working paper titled "Stature and status: Height, ability, and labor market outcomes." (PDF format) In the study Case and Paxson explore what economists have known for a long time: that taller people, on average, earn more money than those who are shorter. For both men and women, an additional inch of height is associated with an increase in earnings of about 2.5 percent. Furthermore, white collar workers are taller, on average, than blue collar workers. In their paper Case and Paxson investigate why this "height advantage" in the labor market exists.
The study authors examined several large data sets from Britain and United States and found that, on average, at very young ages, children who were taller than others of the same age and sex scored better on a wide variety of cognitive tests. Furthermore, the greater earnings of these taller children (who, on average, became taller adults) could be largely explained by their better cognitive test scores as children.
A large number of hypotheses have been put forward to explain the association between height and earnings. In developed countries, researchers have emphasized factors such as self esteem, social dominance, and discrimination. But in their paper, Case and Paxson present evidence that taller people earn more on average because of their tendancy to develop better cognitive skills as children. Their research stresses the roles that health and nutrition in early childhood and in utero have in influencing both height and cognitive ability.
In September Professors Case and Paxson were interviewed by WWS External Affairs about the study and its policy implications.
Woodrow Wilson School (WWS): In your study you find that taller people are smarter than short people. How did you reach this conclusion? Is this genetic; or is this a result of health, poverty, or other environmental conditions?
Anne Case (AC): I'm glad you asked the question in that way, since that is actually not what we find. What we find is that on average - from early childhood to adulthood - taller people score higher on a whole battery of cognitive tests that predict greater labor market success. The "on average" qualifier here is essential. Height is determined both by genes and by health and nutrition in utero and in childhood. Our results say nothing about the relationship between cognitive ability and that part of height that is determined by genetic background. Our results speak to that part of height that is driven by health and nutrition. There are very many very smart short people (Einstein comes to mind) and, frankly, many not-so-smart tall people. We have no reason to think that children who are well-nourished and healthy, but who are short due to genetic factors, will have lower average cognitive test scores.
WWS: What kind of data did you examine? Are your results true for developed as well as developing countries?
Christina Paxson (CP): Economists have generally thought about labor markets in developing countries - where a high proportion of jobs are in agriculture, which may benefit from greater physical strength - when discussing why taller people earn more. What surprised us when we started our work was that a height premium is consistently found in wealthy countries where far fewer people are engaged in manual labor. Our data come from the US and the UK. We have access to two remarkable British data sets that have followed thousands of children born in Britain in 1958 and in 1970 from birth through to middle age. When these children were very young, they took tests of cognitive development, and were measured by doctors. These studies have also collected information on the earnings and employment of these children, who are now adults in their 30s and 40s. The greater earnings of taller children - who, on average, became taller adults - is largely explained by their better cognitive test scores as children; taller adults do not earn any more on average than shorter adults who had the same test scores as children.
WWS: What are these cognitive tests and what did they measure?
AC: The tests administered to children are thought to measure different aspects of cognitive ability. For example, the children born in 1970 took the following tests at age five: a human figure drawing test - the "draw the man" test - which is designed to test conceptual maturity; and a copy design test that measures visual-motor coordination; and the English Picture Vocabulary Test (EPVT) score, which measures the size of the child's vocabulary. These three tests at age five are highly predictive of earnings at age 30. Note, however, that none of the tests we studied were IQ tests.
WWS: If adult height is sensitive to environmental conditions experienced in the womb and in childhood, what are the most critical time periods for physical growth? What are some of the risk factors that could impede adult height?
CP: Health and nutrition in utero and in early childhood - from birth to age three - are critical periods for both cognitive development and growth. Children reach half of their adult height on average by age four and, in general, height not gained by that point cannot be added later. As for risk factors, there is strong evidence that mother's smoking while pregnant, for example, has lasting consequences both for fetal growth and for neural development. Poor nutrition at early ages, and poor health - inflammatory diseases for example - have important effects on growth and, so, on adult height.
WWS: So, are shorter people generally less intelligent than tall people? And how does this relate to height differences in men and women, if at all?
AC: Our evidence indicates that there is a correlation between cognitive test scores and height. This does not imply that all taller children have higher tests scores than all shorter children. For example, there is no reason to think that children who are shorter for genetic reasons should face any disadvantage on cognitive tests. In the US and UK, the relationship between height and cognitive test scores in childhood could not be explained by race, ethnicity, or the sex of the child. The fact that girls are typically shorter than boys has no implications for their test scores. In fact, girls and boys had very similar average scores on all of the tests we examined.
WWS: What are the implications of the study for policy makers, in the U.S. or abroad?
CP: This research has important implications for the intergenerational transmission of poverty. If poorer children are at a nutritional disadvantage in childhood, this may translate into lower earnings capacity as adults, via the impact that the nutritional disadvantage has on cognitive development. This should be of first-order importance to policy makers.
AC: The other important implication is for health policy. Interventions that improve prenatal and early childhood nutrition and health may produce children who are not only taller, but more importantly, who are better able to learn. Gains in cognitive skills that come from health and nutrition interventions may allow children to become more successful adults. So, investing in early childhood health and nutrition may have big payoffs when children become adults.
WWS: If a child has poor health, poor nutrition, or is raised in impoverished conditions early in life, is it possible for them to "catch up" with their healthier counterparts in terms of their cognitive abilities?
AC: Research by others to date has found that children who face difficult health and nutrition environments as young children score less well on cognitive tests throughout childhood and into adulthood. But that does not mean that cognitive "catch up" is not possible. It only means that cognitive catch up generally doesn't occur - not that it couldn't occur through effective intervention.
WWS: Will you continue researching this topic?
CP: There is a great deal of interest in height, and what it can tell us about the extent to which economic resources, public health interventions, and the environment affect health status - both historically and within and between countries today. We plan to continue to contribute to this effort.AC: Documenting one of the ways in which poor health and nutrition in utero and in early childhood has life-long effects on poor children doesn't strike either of us as especially controversial. I think it contributes to efforts to dispel the myth that all children here start life at equal advantage.