With climate change, heat more than natural disasters will drive people away (PNAS)

By Morgan Kelly, Office of Communications

Although scenes of people fleeing from dramatic displays of Mother Nature’s power dominate the news, gradual increases in an area’s overall temperature — and to a lesser extent precipitation — actually lead more often to permanent population shifts, according to Princeton University research.

The researchers examined 15 years of migration data for more than 7,000 families in Indonesia and found that increases in temperature and, to a lesser extent, rainfall influenced a family’s decision to permanently migrate to another of the country’s provinces. They report in the journal the Proceedings of the National Academy of Sciences that increases in average yearly temperature took a detrimental toll on people’s economic wellbeing. On the other hand, natural disasters such as floods and earthquakes had a much smaller to non-existent impact on permanent moves, suggesting that during natural disasters relocation was most often temporary as people sought refuge in other areas of the country before returning home to rebuild their lives.

The results suggest that the consequences of climate change will likely be more subtle and permanent than is popularly believed, explained first author Pratikshya Bohra-Mishra, a postdoctoral research associate in the Program in Science, Technology and Environmental Policy (STEP) in Princeton’s Woodrow Wilson School of Public and International Affairs. The effects likely won’t be limited to low-lying areas or developing countries that are unprepared for an uptick in hurricanes, floods and other natural disasters, she said.

“We do not think of ‘environmental migrants’ in a broader sense; images of refugees from natural disasters often dominate the overall picture,” Bohra-Mishra said. “It is important to understand the often less conspicuous and gradual effect of climate change on migration. Our study suggests that in areas that are already hot, a further increase in temperature will increase the likelihood that more people will move out.”

Indonesia’s tropical climate and dependence on agriculture may amplify the role of temperature as a migration factor, Bohra-Mishra said. However, existing research shows that climate-driven changes in crop yields can effect Mexican migration to the United States, and that extreme temperature had a role in the long-term migration of males in rural Pakistan.

“Based on these emerging findings, it is likely that the societal reach of climate change could be much broader to include warm regions that are now relatively safe from natural disasters,” Bohra-Mishra said.

Indonesia became the case study because the multi-island tropical nation is vulnerable to climate change and events such as earthquakes and landslides. In addition, the Indonesian Family Life Survey (IFLS) conducted by the RAND Corporation from 1993 to 2007 provided thorough information about the movements of 7,185 families from 13 of the nation’s 27 provinces in 1993. The Princeton researchers matched province-to-province movement of households over 15 years to data on temperature, precipitation and natural disasters from those same years. Bohra-Mishra worked with co-authors Michael Oppenheimer, the Albert G. Millbank Professor of Geosciences and International Affairs and director of STEP, and Solomon Hsiang, a past Princeton postdoctoral researcher now an assistant professor of public policy at the University of California-Berkeley.

People start to rethink their location with each degree that the average annual temperature rises above 25 degrees Celsius (77 degrees Fahrenheit), the researchers found. The chances that a family will leave an area for good in a given year rise with each degree. With a change from 26 to 27 degrees Celsius (78.8 to 80.6 Fahrenheit), the probability of a family emigrating that year increased by 0.8 percent when other factors for migration were controlled for. From 27 to 28 degrees Celsius (80.6 to 82.4 Fahrenheit), those chances jumped to 1.4 percent.

When it comes to annual rainfall, families seem to tolerate and prefer an average of 2.2 meters (7.2 feet). The chances of outmigration increased with each additional meter of average annual precipitation, as well as with further declines in rainfall.

Landslides were the only natural disaster with a consistent positive influence on permanent migration. With every 1 percent increase in the number of deaths or destroyed houses in a family’s home province, the likelihood of permanent migration went up by only 0.0006 and 0.0004 percent, respectively.

The much higher influence of heat on permanent migration can be pinned on its effect on local economies and social structures, the researchers write. Previous research has shown that a one-degree change in the average growing-season temperature can reduce yields of certain crops by as much as 17 percent. At the same time, research conducted by Hsiang while at Princeton and published in 2013 showed a correlation between higher temperatures and social conflict such as civil wars, ethnic conflict and street crime.

In the current study, the researchers found that in Indonesia, a shift from 25 to 26 degrees Celsius resulted in a significant 14 to 15 percent decline in the value of household assets, for example. Precipitation did not have a notable affect on household worth, nor did natural disasters except landslides, which lowered assets by 5 percent for each 1 percent increase in the number of people who died.

Read the abstract.

Bohra-Mishra, Pratikshya, Michael Oppenheimer, Solomon Hsiang. 2014. Nonlinear permanent migration response to climatic variations but minimal response to disasters. Proceedings of the National Academy of Sciences. Article published online June 23, 2014. DOI: 10.1073/pnas.1317166111.

Migrating north may trigger immediate health declines among Mexicans (Demography)

Mexican-Square_351x351_45
Photo credit: Ticiana Jardim Marini, Woodrow Wilson School

By B. Rose Huber, Woodrow Wilson School of Public and International Affairs

Mexican immigrants who relocate to the United States often face barriers like poorly paying jobs, crowded housing and family separation. Such obstacles – including the migration process itself – may be detrimental to the health of Mexican immigrants, especially those who have recently moved.

A study led by Princeton University’s Woodrow Wilson School of Public and International Affairs finds that Mexican immigrants who relocate to the United States are more likely to experience declines in health within a short time period compared with other Mexicans.

While past studies have attempted to examine the consequences of immigration for a person’s health, few have had adequate data to compare recent Mexican immigrants, those who moved years ago and individuals who never left Mexico. Published in the journal Demography, the Princeton-led study is one of the first to examine self-reported health at two stages among these groups.

“Our study demonstrates that declines in health appear quickly after migrants’ arrival in the United States,” said Noreen Goldman, lead author and professor of demography and public affairs at the Wilson School and faculty associate at the Wilson School’s Office of Population Research (OPR). “Overall, we find that recent Mexican migrants are more likely to experience rapid changes in health, both good and bad, than the other groups. The deteriorations in health within a year or two of migration far outweigh the improvements.”

For the study, the researchers used data from the Mexican Family Life Survey, a longitudinal survey containing demographic and health information on nearly 20,000 Mexicans who were 20 years or older at the time of the first interview in 2002. Follow-up interviews took place in 2005-06 with individuals who stayed in Mexico as well as with those who moved to the United States between 2002 and 2005. Goldman and her collaborators based their analysis on a sample of 14,257 adults, excluding those who didn’t report health conditions at the follow-up interview.

In order to assess whether migrants from Mexico to the United States experienced changes in their health after they moved, the researchers used two health assessments: self-rated health (compared to someone of the same age and sex) at each of the two interviews and perceived change in health at the second interview. The latter measure was based on the following question: “Comparing your health to a year ago, would you say your health is much better, better, the same, worse or much worse?” Goldman and her collaborators narrowed the original five response categories to three: better, worse or the same. Changes in health for Mexicans who migrated between 2002 to 2005 were compared with those of migrants from earlier time periods and with people who remained in Mexico.

The researchers also took health measures at the first wave into account: obesity, anemia, hypertension – which were all determined by at-home visits by trained health workers – and hospitalization within the past year. They also controlled for socioeconomic factors – years of schooling and household spending. Additionally, they included data from 136 municipalities in Mexico (as past research has found that migration decisions can differ based on place of origin.)

Using statistical models, the researchers analyzed changes in health status. The two health measures revealed that recent migrants to the United States were more apt to experience both improvements and declines in their health than either earlier migrants or non-migrants. However, the overall net change was a substantial deterioration in the health of recent migrants relative to the other groups. The health of recent migrants was about 60 percent more likely to have worsened within a one- or two-year period than that of those who never left Mexico.

“The speed of the health decline for recent migrants suggests that the process of border crossing for both documented and undocumented immigrants combined with the physical and psychological costs of finding work, crowded housing, limited access to health care in the United States and isolation from family members can result in rapid deterioration of immigrants’ physical and mental wellbeing,” said Goldman.

“Immigrants are often assumed to be resilient and in good health because they have not yet adopted unhealthy American behaviors like poor diet and a sedentary lifestyle,” said co-author Anne Pebley from the California Center for Population Research at the University of California, Los Angeles. “But these results suggest that the image of the ‘healthy migrant’ is an illusion – at least for many recent immigrants.”

“These results demonstrate the high personal costs that many immigrants are willing to pay for a chance to improve their lives,” said Goldman. “From a humanitarian standpoint, the health declines underscore the need for public health, social service and immigration agencies to provide basic services for physical and psychological health to recent migrants.”

Given the limitations of the dataset, Goldman and her collaborators could not provide a more nuanced analysis regarding the causes of the changes in health status, but, with the availability of the third wave of data (collected between 2009-12), many of these questions can be later addressed.

In addition to Goldman and Pebley, study researchers include Chang Chung from OPR; Mathew Creighton from the University of Massachusetts; Graciela Teruel from the Universidad Iberoamericana; and Luis Rubalcava from the Centro de Análisis y Medición del Bienestar Social.

Support for this project from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (R01HD051764, R24HD047879, R03HD040906, and R01HD047522) and from the Sector Research Fund for Social Development of the National Council for Science and Technology of Mexico.

Read the abstract.

Goldman N, Pebley AR, Creighton MJ, Teruel GM, Rubalcava LN, Chung C. 2014. The Consequences of Migration to the United States for Short-Term Changes in the Health of Mexican Immigrants. Demography. 2014 May 1 (Epub ahead of print).

Death of an adult son increases depressive symptoms in mothers, but not fathers (Social Science and Medicine)

Sad mother picture
A study by researchers at Princeton and Georgetown Universities found that Taiwanese mothers – but not fathers – experience depressive symptoms after an adult son’s death, while the death of a daughter had no such effect on either parent.

By B. Rose Huber, Woodrow Wilson School of Public and International Affairs

Mothers – but not fathers – exhibited symptoms of depression and experienced declines in overall health after the death of an adult son, while the death of a daughter had no such effect on either parent, according to one of the first studies to examine the impacts of the death of an adult child on parents aged 65 and older.

In East Asian cultures, an adult son’s role in the family is crucial to the wellbeing and financial stability of his parents, the researchers suggest. Therefore, a traumatic event, like the death of a son, could place quite a strain on elderly parents living in these cultures – particularly women, especially if the deceased son is the eldest or only son.

The researchers, from the Office of Population Research in Princeton University’s Woodrow Wilson School, published their findings in the journal Social Science & Medicine based on data from the Taiwanese Longitudinal Study of Aging, a nationally representative survey designed to assess the health of older people in Taiwan.

“In East Asian cultures like Taiwan, sons hold the primary responsibility for providing financial and instrumental assistance to their elderly parents,” said lead author Chioun Lee, a Princeton postdoctoral research associate. “Older women who have had particularly few educational and occupational opportunities are more likely to rely on their sons for support. Therefore, a traumatic event, like a son’s death, could place quite a strain on a mother’s health.”

Along with study coauthor Noreen Goldman, the Hughes-Rogers Professor of Demography and Public Affairs at WWS, and researchers from Georgetown University, Lee used data collected for the Taiwanese Longitudinal Study of Aging from 1996 to 2007, which included approximately 4,200 participants.

To evaluate parental wellbeing, they used two self-reported measures: one for overall health and another for depressive symptoms. Each respondent’s health was assessed based on the following question: “Regarding your current state of health, do you feel it is excellent, good, average, not so good, or poor?” The items were coded on a one-to-five-point scale with higher scores indicating better health. Past studies have indicated that this measure is a strong predictor of mortality.

Depressive symptoms were measured with an eight-item subset of the Center for Epidemiological Studies Depression Scale, which asks participants to report how often they’ve experienced various situations or feelings in the past week. Possible answers range from “0,” which means rarely or none of the time, to “3,” which is most or all of the time. Higher scores for the eight items indicate more frequent depressive symptoms.

The researchers controlled for parental wellbeing prior to the death of a child and analyzed the data in two stages. First, they tested the extent to which a child’s death affected a parent’s health and then whether that varied by the parent’s sex. Finally, they determined the influence of a deceased child’s sex on parental wellbeing.

They found that women who lost a son scored, on average, 2.4 points higher on levels of depressive symptoms than those who did not lose a child. For men, there were no significant differences. There was no evidence to suggest that either mothers or fathers were significantly affected by depressive symptoms or declines in reports of overall health following the death of a daughter. Lee explains that while finances are a concern, there may be other factors at play.

“I also think that various attributes of deceased children, such as birth order, affective bonds with their parents or cause of death, might influence parental wellbeing,” said Lee, who is a native of Korea and observed son preference and gender inequality throughout her childhood.

According to Goldman, these findings underscore the continued gender inequality in Taiwan.

“Despite large advances in women’s labor market participation and educational attainment in recent years – for example, women in Taiwan are now more likely than men to hold a higher education degree – son preference persists, affecting various aspects of women’s well-being,” Goldman said.

Read the abstract.

Lee, C., et al., Death of a child and parental wellbeing in old age: Evidence from Taiwan, Social Science & Medicine (2013), http://dx.doi.org/10.1016/jsocscimed.2013.08.007

The work was funded by the Demography and Epidemiology Unit of the Division of Behavioral and Social Research at the National Institute on Aging and the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

More or less equal? How men factor into the reproductive equation (Gender & Society)

A new study calls attention to the role of men’s behavior and health in reproductive outcomes, such as fetal health, birth defects and childhood diseases. (Image credit: CDC/Amanda Mills)
A new study calls attention to the role of men’s behavior and health in reproductive outcomes, such as fetal health, birth defects and childhood diseases. (Image credit: CDC/Amanda Mills)

By Bess Connolly Martell, Office of Public Affairs and Communications, Yale University

Researchers know a lot about how women’s bodily health affects their fertility, but less is known about how men’s health affects reproductive outcomes. Yale University researcher Rene Almeling and co-author Miranda Waggoner of Princeton University address this discrepancy in an article published Tuesday, Dec. 3, in the journal Gender & Society.

In the period before conception, family health history and current health behaviors matter for women and men alike, say the researchers, adding that more clinical research needs to be done on how men’s bodily health affects their sperm, and in turn, reproductive health outcomes.

“The lack of attention to men in research on reproduction leaves open many important questions, including how men’s reproductive contributions are understood,” say Almeling, an assistant professor of sociology at Yale, and Waggoner, a postdoctoral researcher in the Office of Population Research in the Woodrow Wilson School of Public and International Affairs at Princeton.

The vast majority of medical and social science research on reproduction focuses on women. It wasn’t until recently that scientists began studying the role that men’s behavior and men’s health play in reproductive outcomes, such as fetal health, birth defects and childhood diseases.

The stereotypical association of women with family and men with work has led to a focus on women’s bodies in reproduction, leaving the question of how men’s health contributes to reproduction unanswered.

“What kinds of advice, if any, do men receive about preparing their bodies for reproduction?” ask the researchers. “Men should be empowered with information about how their age, health history and unhealthy behaviors can affect pregnancy outcomes.”

The sperm bank is one of the few places where men’s reproductive health takes center stage, the researchers note. At sperm banks, men are counseled on healthy eating, avoiding stress and reducing alcohol consumption. Not adhering to this advice can and does lead to lower sperm counts, suggesting that this kind of guidance might be more broadly useful for men trying to conceive children with their partners.

There are also associated policy implications. The Affordable Care Act stipulates that women with private insurance are no longer required to pay for preconception health appointments, but excluding men from such coverage continues to obscure their role in reproduction, say Almeling and Waggoner. “Paying attention to how reproductive equations influence policy can suggest new and different avenues for improving public health,” say the sociologists. They add, “Recent public health initiatives devoted to preconception care offer at least the possibility that men’s reproductive contributions will be considered alongside women’s.”

Read the abstract.

Almeling, Rene and Miranda R. Waggoner. More and Less than Equal: How Men Factor in the Reproductive Equation. Gender & Society December 2013 27: 821-842, first published on April 25, 2013 doi:10.1177/0891243213484510.

Both authors received funding from the National Science Foundation (Almeling grant #0602871 and Waggoner grant #1029087), and Miranda Waggoner also received support from the National Institutes of Health (T32 HD007163).

Small declines in agility, facial features may predict risk of dying (Epidemiology)

Photo source: Shutter Stock
Photo source: Shutter Stock

By B. Rose Huber, Woodrow Wilson School of Public and International Affairs

A new study from Princeton University shows that health assessments made by medically untrained interviewers may predict the mortality of individuals better than those made by physicians or the individuals themselves.

Features like forehead wrinkles and lack of agility may reflect a person’s overall health and risk of dying, according to recent health research. But do physicians consider such details when assessing patients’ overall health and functioning?

In a survey of approximately 1,200 Taiwanese participants, Princeton University researchers found that interviewers — who were not health professionals but were trained to administer the survey — provided health assessments that were related to a survey participant’s risk of dying, in part because they were attuned to facial expressions, responsiveness and overall agility.

The researchers report in the journal Epidemiology that these assessments were even more accurate predictors of dying than assessments made by physicians or even the individuals themselves. The findings show that survey interviewers, who typically spend a fair amount of time observing participants, can glean important information regarding participants’ health through thorough observations.

“Your face and body reveal a lot about your life. We speculate that a lot of information about a person’s health is reflected in their face, movements, speech and functioning, as well as in the information explicitly collected during interviews,” said Noreen Goldman, Hughes-Rogers Professor of Demography and Public Affairs in the Woodrow Wilson School.

Together with lead author of the paper, Princeton Ph.D. candidate Megan Todd, Goldman analyzed data collected by the Social Environment and Biomarkers of Aging Study (SEBAS). This study was designed by Goldman and co-investigator Maxine Weinstein at Georgetown University to evaluate the linkages among the social environment, stress and health. Beginning in 2000, SEBAS conducted extensive home interviews, collected biological specimens and administered medical examinations with middle-aged and older adults in Taiwan. Goldman and Todd used the 2006 wave of this study, which included both interviewer and physician assessments, for their analysis. They also included death registration data through 2011 to ascertain the survival status of those interviewed.

The survey used in the study included detailed questions regarding participants’ health conditions and social environment. Participants’ physical functioning was evaluated through tasks that determined, for example, their walking speed and grip strength. Health assessments were elicited from participants, interviewers and physicians on identical five-point scales by asking “Regarding your/the respondent’s current state of health, do you feel it is excellent (5), good (4), average (3), not so good (2) or poor (1)?”

Participants answered this question near the beginning of the interview, before other health questions were asked. Interviewers assessed the participants’ health at the end of the survey, after administering the questionnaire and evaluating participants’ performance on a set of tasks, such as walking a short distance and getting up and down from a chair. And physicians — who were hired by the study and were not the participants’ primary care physicians — provided their assessments after physical exams and reviews of the participants’ medical histories. (Study investigators did not provide special guidance about how to rate overall health to any group.)

In order to understand the many variables that go into predicting mortality, Goldman and Todd factored into their statistical models such socio-demographic variables as gender, place of residence, education, marital status, and participation in social activities. They also considered chronic conditions, psychological wellbeing (such as depressive symptoms) and physical functioning to account for a fuller picture of health.

“Mortality is easy to measure because we have death records indicating when a person has died,” Goldman said. “Overall health, on the other hand, is very complicated to measure but obviously very important for addressing health policy issues.”

Two unexpected results emerged from Goldman and Todd’s analysis. The first: physicians’ ratings proved to be weak predictors of survival. “The physicians performed a medical exam equivalent to an annual physical exam, plus an abdominal ultrasound; they have specialized knowledge regarding health conditions,” Goldman explained. “Given access to such information, we anticipated stronger, more accurate predictions of death,” she said. “These results call into question previous studies’ assumptions that physicians’ ‘objective health’ ratings are superior to ‘subjective’ ratings provided by the survey participants themselves.”

In a second surprising finding, the team found that interviewers’ ratings were considerably more powerful for predicting mortality than self-ratings. This is likely, Goldman said, because interviewers considered respondents’ movements, appearance and responsiveness in addition to the detailed health information gathered during the interviews. Also, Goldman posits, interviewer ratings are probably less affected by bias than self-reports.

“The ‘self-rated health’ question is religiously used by health researchers and social scientists, and, although it has been shown to predict mortality, it suffers from many biases. People use it because it’s easy and simple,” Goldman continued. “But the problem with self-rated health is that we have no idea what reference group the respondent is using when evaluating his or her own health. Different ethnic and racial groups respond differently as do varying socioeconomic groups. We need other simple ways to rate individual health instead of relying so heavily on self-rated health.”

One way, Goldman suggests, is by including interviewer ratings in surveys along with self-ratings: “This is a straightforward and cost-free addition to a questionnaire that is likely to improve our measurement of health in any population,” Goldman said.

The paper, “Do Interviewer and Physician Health Ratings Predict Mortality? A Comparison with Self-Rated Health,” first appeared online in Epidemology in August 2013. The article also will be featured in the November print edition. The research was conducted with the assistance of colleagues at Princeton’s Office of Population Research, Georgetown University and the Bureau of Health Promotion in the Taiwan Department of Health.

Read the abstract.

Todd MA, Goldman N. Do interviewer and physician health ratings predict mortality?: a comparison with self-rated health. Epidemiology. 2013 Nov;24(6):913-20. doi: 10.1097/EDE.0b013e3182a713a8.

 

Princeton researchers use mobile phones to measure happiness (Demography)

By Tara Thean, Science-Writing Intern, Office of the Dean for Research

World map
Locations of study subjects on world map (Source: Demography)

Researchers at Princeton University are developing ways to use mobile phones to explore how one’s environment influences one’s sense of well-being.

In a study involving volunteers who agreed to provide information about their feelings and locations, the researchers found that cell phones can efficiently capture information that is otherwise difficult to record, given today’s on-the-go lifestyle. This is important, according to the researchers, because feelings recorded “in the moment” are likely to be more accurate than feelings jotted down after the fact.

To conduct the study, the team created an application for the Android operating system that documented each person’s location and periodically sent the question, “How happy are you?”

The investigators invited people to download the app, and over a three-week period, collected information from 270 volunteers in 13 countries who were asked to rate their happiness on a scale of 0 to 5. From the information collected, the researchers created and fine-tuned methods that could lead to a better understanding of how our environments influence emotional well-being. The study was published in the June issue of Demography.

The mobile phone method could help overcome some of the limitations that come with surveys conducted at people’s homes, according to the researchers. Census measurements tie people to specific areas — the census tracts in which they live — that are usually not the only areas that people actually frequent.

“People spend a significant amount of time outside their census tracks,” said John Palmer, a graduate student in the Woodrow Wilson School of Public and International Affairs and the paper’s lead author. “If we want to get more precise findings of contextual measurements we need to use techniques like this.”

Palmer teamed up with Thomas Espenshade, professor of sociology emeritus, and Frederic Bartumeus, a specialist in movement ecology at the Center for Advanced Studies of Blanes in Spain, along with Princeton’s Chang Chung, a statistical programmer and data archivist in the Office of Population Research; Necati Ozgencil, a former Professional Specialist at Princeton; and Kathleen Li, who earned her undergraduate degree in computer science from Princeton in 2010, to design the free, open source application for the Android platform that would record participants’ locations at various intervals based on either GPS satellites or cellular tower signals.

Though many of the volunteers lived in the United States, some were in Australia, Canada, China, France, Germany, Israel, Japan, Norway, South Korea, Spain, Sweden and the United Kingdom.

Palmer noted that the team’s focus at this stage was not on generalizable conclusions about the link between environment and happiness, but rather on learning more about the mobile phone’s capabilities for data collection. “I’d be hesitant to try to extend our substantive findings beyond those people who volunteered.” he said.

However, the team did obtain some preliminary results regarding happiness: for example, male subjects tended to describe themselves as less happy when they were further from their homes, whereas females did not demonstrate a particular trend with regards to emotions and distance.

“One of the limitations of the study is that it is not representative of all people,” Palmer said. Participants had to have smartphones and be Internet users. It is also possible that people who were happy were more likely to respond to the survey. However, Palmer said, the study demonstrates the potential for mobile phone research to reach groups of people that may be less accessible by paper surveys or interviews.

Palmer’s doctoral dissertation will expand on this research, and his adviser Marta Tienda, the Maurice P. During Professor in Demographic Studies, said she was excited to see how it will impact the academic community. “His applied research promises to redefine how social scientists understand intergroup relations on many levels,” she said.

This study involved contributions from the Center for Information Technology Policy at Princeton University, with institutional support from the National Institutes of Health Training Grant T32HD07163 and Infrastructure Grant R24HD047879.

Read the abstract.

Palmer, John R. B., Thomas J. Espenshade, Frederic Bartumeus, Chang Y. Chung, Necati Ercan Ozgencil and Kathleen Li. 2013. New Approaches to Human Mobility: Using Mobile Phones for Demographic Research. Demography 50:1105–1128. DOI 10.1007/s13524-012-0175-z