L. Asad

Network Effects in Mexico–U.S. Migration Disentangling the Underlying Social Mechanisms

Scholars have long noted how migration streams, once initiated, obtain a self-feeding character. Studies have connected this phenomenon, called the cumulative causation of migration, to expanding social networks that link migrants in destination to individuals in origin. While extant research has established a positive association between individuals’ ties to prior migrants and their migration propensities, seldom have researchers interrogated how multiple social mechanisms—as well as exposure to common environmental factors—might account for these interdependencies. This article uses a mixed-methods strategy to identify the social mechanisms underlying the network effects in Mexico–U.S. migration. Three types of social mechanisms are identified, which all lead to network effects: (a) social facilitation, which is at work when network peers such as family or community members provide useful information or help that reduces the costs or increases the benefits of migration; (b) normative influence, which operates when network peers offer social rewards or impose sanctions to encourage or discourage migration; and (c) network externalities, which are at work when prior migrants generate a pool of common resources that increase the value or reduce the costs of migration for potential migrants. The authors first use large-sample survey data from the Mexican Migration Project to establish the presence of network effects and then rely on 138 in-depth interviews with migrants and their family members in Mexico to identify the social mechanisms underlying these network effects. The authors thus provide a deeper understanding of migration as a social process, which they argue is crucial for anticipating and responding to future flows.

Association of Post-Traumatic Stress Disorder Symptoms with Migraine and Headache after a Natural Disaster

OBJECTIVE Previous research shows that migraine and general headache symptoms increase after traumatic events. Questions remain about whether posttraumatic stress disorder (PTSD) produces migraine/headache symptoms, or if individuals afflicted by migraine/headache are especially likely to develop PTSD. We test whether PTSD symptoms following a natural disaster are associated with higher odds of reporting frequent headaches/migraines postdisaster. We decompose PTSD into intrusion, avoidance, and hyperarousal symptom clusters to examine which, if any, are uniquely related to headache/migraine postdisaster. METHOD We use prospectively collected pre- and postdisaster data to explore whether overall PTSD symptoms and symptom clusters are associated with migraine/headache in a sample of Hurricane Katrina survivors. We account for severity of hurricane exposure and control for baseline migraine and headache problems to reduce the probability that heightened PTSD susceptibility among those who already suffered from the conditions could explain observed associations. RESULTS PTSD symptoms were associated with higher odds of experiencing frequent headaches or migraines with a standard deviation change in PTSD score corresponding to over twice the odds (95% confidence interval [1.64, 2.68]) of having trouble with frequent headaches or migraines in the post-Katrina period. Each additional point on the intrusion subscale (sample M [SD] = 1.6 [1.1]) was associated with 55% higher odds of reporting frequent headache/migraine (95% confidence interval [1.03, 2.33]), but we found no association with avoidance or hyperarousal symptoms. CONCLUSIONS Clinicians and disaster planners should be aware that disaster survivors might be at heightened risk of migraine/headache episodes, and those experiencing intrusive reminders may be most affected. (PsycINFO Database Record

The Relational Basis of Neighborhood Selection: How Social Ties Shape Residential Migration and Mobility Outcomes for Low-Income Families

Why, when given the opportunity to move from high- to low-poverty neighborhoods, do some low-income families return to disadvantaged settings? Extant literature emphasizes low-income families’ “reactive” migration to structural forces beyond their control. But social ties are in fact a component of social structure that may be a relevant resource for low-income families’ residential migration decisions. Drawing on longitudinal geographic, interview, and social network data with 75 low-income mothers who survived Hurricane Katrina, I find the importance of social ties is magnified in situations of unplanned moves. Network peers from the origin neighborhood provide information or help that minimize the costs and increase the expected benefits of residential migration after initial displacement. In the absence of social ties, a family may evaluate the costs of settlement in the new environment to be too high and “re-optimize” by moving to a neighborhood that maximizes proximity to social resources. In some cases, this tradeoff is an undesirable but necessary reality for low-income families who feel pressured to be closer to their network peers. These findings suggest that scholars and policymakers should reconsider how social networks shape residential migration and mobility, as well as what it means to live in a disadvantaged neighborhood.