Postdoc Spotlight: Esmée Zwiers

Written by
Aimee Bronfeld
Nov. 4, 2020

Nature or nurture? Esmée Zwiers is fascinated by this age-old debate about the forces that drive human behavior. An economist with broad interests in labor and health economics, her postdoctoral research at the Center for Health and Wellbeing (CHW) studies the meaningful, often measurable ways in which biological and environmental factors shape people’s lives – from their fertility to their academic performance, job opportunities, and behavioral health.

In this interview, Esmée shares her burgeoning body of work on human capital formation and other dynamics that impact maternal-child outcomes, while probing the curious connection between family and fate.

Q. Your doctoral research, which we’ll delve into a bit later, argues that the environment in which you grow up has a substantial impact on where you end up in life. With that in mind, do you feel that your personal background has affected your perspectives and research related to health economics?

A. I do. I grew up in a small, quiet town in the urban, western part of the Netherlands, where everyone has access to health insurance and affordable health care, regardless of employment status. Citizens worry little about the costs associated with illness or hospitalizations, which is very different than the health care system in the United States and other countries.

I was also privileged in the sense that I was raised by a loving family with the means to support my education, hobbies, and career choices. As part of a diverse community, I realized that many other kids did not have the same opportunities. My parents taught me to see beyond those disparities, to understand that everyone is equal regardless of background, ethnicity, or socioeconomic status. In hindsight, I think those circumstances and values influenced my views on global health and social issues.

Q. You devoted nine years to higher education, eventually earning a Ph.D in Economics at Erasmus University Rotterdam and the Tinbergen Institute. What drew you to this field of study and a career in academia?

A. It probably boils down to curiosity. As a child, I saw my parents read the newspaper every morning and watch the news every night, giving me exposure to current events and the world around me. I thoroughly enjoyed asking questions and writing about everything, from volcanoes to tattoos. This probably sparked my interest in research.


I was initially planning a career in business. In fact, at one point I was thinking about marketing. I shifted to economics because I was intrigued by social problems, especially within the context of public policy. The biggest turning point occurred when I took a course in policy evaluation, learning about the different methods that can be used to causally infer if a particular policy is effective or not. It taught me how to use natural experiments, demography, and other tools to establish whether “x” causally affects “y.” For example, how can we use these methodologies to evaluate the effect of education on earnings? I loved that course; it helped me realize what I wanted to do for the rest of my life.

Q. Tell me about your dissertation examining the link between childhood circumstances and human capital formation. What was the crux of your study?


A. The subject evolved over the course of my Ph.D. research, but generally explored the role of family on fate. I used quasi-experimental evidence to examine how various childhood factors affect a child’s human capital formation, from pre-conception to later in life. To do this, I evaluated how the absence or presence of childhood circumstance “x,” such as economic stability, may have impacted outcome “y,” such as fertility or educational attainment.

My findings, based on data from the Netherlands, answered some questions and raised others. Overall, they support the theory that the environment in which one grows up impacts future outcomes, suggesting that nurture is just as important – if not more important – than nature, and that early inequalities may amplify in adulthood.

Q. Can you elaborate on your findings, highlighting conclusions that were especially significant or perhaps unexpected?


A. First, I studied how improved socioeconomic conditions at the end of World War II [in the Netherlands] may have influenced parental selection. In other words, which types of parents had a child in the aftermath of the war and how did this affect the long-term outcomes of their children? Surprisingly, I did not find evidence that the better socioeconomic circumstances that came with the end of the war affected selection into parenthood, or that children who grew up in a less stable family environment experienced poorer health or labor market outcomes in late adulthood.

I also studied gender differences in educational performance with my co-author Anne Gielen from Erasmus University Rotterdam. Research in rodents has shown that testosterone transfers in-utero from a male twin to his female sibling. Using that finding and the premise that boys have traditionally achieved better outcomes in math, we conducted a biological experiment to see if girls exposed to prenatal testosterone received higher test scores. We found that girls with a twin brother scored slightly lower in math, with no difference in reading. Interestingly, the effects were stronger for girls raised in families characterized by stronger stereotypical gender norms, suggesting that nurture plays an important role in scholastic achievement.      

Finally, I explored how parental aversion to the “last place” impacts the educational outcomes of their children. This study exploits the tracked structure of the Dutch secondary education system. I analyze how a reform, which merged the two lowest tracks, affected variables that determine track allocation: high-stakes standardized tests and teacher recommendations. Results suggest that children perform worse when the pressure to perform well is high.

Q. Did your doctoral research serve as a springboard for your work here at Princeton?  Are you continuing to investigate the intergenerational connections between family and fate?

A. I am. In fact, I’m fascinated by the subject of fertility… learning more about when and why people decide to have children, as well as how those decisions may impact outcomes across generations.

I am currently revising my paper on parental selection following World War II, broadening the study by exploiting regional variation in war circumstances, age of the mother at the time of the Dutch liberation, and other factors that may explain the huge peak in births following liberation. For example, did areas hit by bombings, famine, and other severe circumstances experience a larger increase in post-war fertility, and were those babies born to younger or relatively older mothers?  I’m convinced there are more layers to explore.

A natural continuation of my doctoral research is another project examining the long-term effects of improved access to the birth control pill in the Netherlands. My co-author, Olivier Marie from Erasmus University Rotterdam, and I are analyzing how the ability to control fertility may impact the outcomes of women and their children, such as decisions about marriage, parenthood, education, and work. Uniquely, the study investigates the supply side, which is a new angle that has not yet been presented in the literature. My co-author and I are not merely looking at how relaxed regulations affect the demand for birth control pills, but also how physician beliefs affect the prescribing of contraceptives.

Q. What has been most exciting, so far, about this work investigating the “power of the Dutch pill”?


A. It’s still a work in progress, but we already have some noteworthy results. For example, we find that access to the pill has allowed more Dutch women to avoid “shotgun weddings” and that fewer women become mothers as minors [below age 21 at that time in the Netherlands]. Findings also suggest that contraceptive options for women only improve if they have access to a non-religious health professional because religious “gatekeepers” are nearly three times less likely to prescribe the pill to unmarried women. In future work, we will study the pill’s long-term effects as well. For instance, is there any connection between a mother’s access to contraception and her child’s outcomes related to education, labor, and even crime.

This study is focused on the Netherlands, but its outcomes are relevant to other countries too. The U.S. Supreme Court, for example, recently ruled that employers can opt out of contraceptive coverage based on religious objections, and news outlets have reported that some doctors in Italy are not willing to perform abortions based on their religious beliefs. Hence the interaction between access to family planning and religious beliefs is timely and relevant all over the world.

Q. Why has CHW been a good fit for your research? Have you had the opportunity to engage with other disciplines and partner with any of the center’s affiliates?

A. I first came to CHW when I was working on my Ph.D., as a visiting student research collaborator. I enjoyed that experience a lot and am very grateful that I had the opportunity to return in a postdoctoral position soon after earning my degree. The interdisciplinary flavor and welcoming environment have been beneficial to my research in health and labor economics, allowing me to exchange ideas and knowledge with people working on similar topics and to look at problems from different angles.

I have collaborated with faculty members in the Economics Department and the School of Public and International Affairs. Particularly, it has been such a privilege working with Janet Currie. We recently co-authored a paper on how technology and big data are changing economics as part of the “credibility revolution,” through which the field has shifted its focus toward measuring causal effects. Janet and I also started a project exploring the intergenerational impact of mental health, studying how the mental health of parents influence the outcomes of their children.

Q. You’re currently in your second year as a CHW postdoc. Have you given any thought to what the next chapter may bring, in terms of your research and career plans?

A. On the research side, I am excited about further exploring intergenerational mental health and the idea of selection into parenthood. I think both are very relevant today in the realm of the Covid-19 pandemic. I’m wondering, for example, about how Covid-19 affects fertility and the outcomes of children. For example, when a mother contracts this virus, does it lead to adverse outcomes during pregnancy? How might lockdowns, less access to contraceptives, and closed abortion facilities affect pregnancy and birth rates? How does increased stress of parents - that might come with the pandemic - affect child outcomes? Also, we need to look toward the next generation. It is important to understand how something that happens before a child is even born or in early childhood, whether it is related to a pandemic or any other circumstance, could affect that child’s entire life. This information could be helpful in developing policies to achieve better outcomes for both women and children, and to ultimately improve people’s lives.

More broadly, I hope to write and publish more papers and expand my portfolio to advance my career in academia. I thoroughly enjoy doing research, as well as teaching. It is so gratifying to transfer knowledge to students and see them get excited about economics.

Q. On a lighter and more personal note, anything you might like to share outside your professional pursuits? What do you do for fun?

A. I’m an avid golfer. Aside from satisfying my competitive nature, I love spending hours outside with no phone or worries other than the ball… which generally doesn’t go where you want it to go! The sport offers a great break from work and a welcome escape during these challenging times.