Why are there stable cross-country differences in suicide rates? How can the prevalence of autism increase so rapidly?
Networks are crucial to solving epidemiological puzzles. Medical science presumes biological risk levels drive disease patterns. I challenge this assumption—by showing the diffusion of knowledge about autism shapes its spatial patterns and ruling out competing environmental and biological explanations, I demonstrate that social factors are as important as biological factors. Specifically, I address the classic sociological question of how social interactions generate macro epidemiological patterns, using a wide range of techniques (e.g., agent-based modeling) and large datasets (e.g., administrative, spatial, and online). These methods have also produced innovative findings on the population-level effects of suicide contagion and fertility decisions. My research thereby contributes to diffusion theories and the applications of system science techniques in social epidemiology.
Research interests: Social Diffusion, Social Networks, Medical Sociology, Micro-Macro Links, Geographical Information System
link to my website
D.Phil., University of Oxford
M.Phil., University of Oxford
B.Soc. Sci., University of Hong Kong
Eliot Freidson Outstanding Publication Award, American Sociological Association, Medical Sociology Section, 2011
JK Swire Memorial Scholarship, full D.Phil. Scholarship, 2004-2006
Swire & Cathay Scholarship, full M.Phil. Scholarship, 2000-2002
California Center for Population Research Seed grant (US$16,167).“Estimating the Mortality Rates of Unauthorized Mexican Immigrants in California” role: Principle Investigator. 5/1/2015- 4/30/2016
UCLA Hellman Fellows award (US$24,253). “Diffusion of Non-Medical Exemptions to School Vaccine Requirements in California, 1992-2011” Principle Investigator.7/1/2014-8/30/2016
NIMH-R21 (MH100514-01A1. UCLA direct cost: $113,436; total direct cost US$275,000). “The Spread of Autism Diagnosis through Spatially Embedded Social Networks” Principle Investigator (with Peter Bearman). 1/1/2014-12/31/2016
Liu, Ka Y, Bearman, PS (2015). Focal points, endogenous processes and exogenous shocks in the autism epidemic. Sociological Methods and Research, 44(2) 272-305 [link]
Liu Ka Y, King M, Bearman P (2010). Social influence and the autism epidemic. American Journal of Sociology 115(5):1389-434 [link]
Liu Ka Y, Zerubavel N, Bearman P (2010). Social demographic change and autism. Demography 47(2):327-343 [link]
Hedström, P, Liu, Ka Y, Nordvik, M.(2008) Interaction domains and suicides: A population-based panel study of suicides in Stockholm, 1991-1999. Social Forces 87(2):713-740 [link]
Liu Ka Y, Beautrais A, Caine E, et al. (2007). Charcoal burning suicides in Hong Kong and urban Taiwan – An illustration of the impact of a novel method of suicide on overall regional rates.Journal of Epidemiology and Community Health 61:248-53 [link]
Liu Ka Y, Chen E, Chan C et al. (2006). Socio-economic and psychological correlates of suicidality among Hong Kong working-age adults: results from a population-based survey.Psychological Medicine 36: 1759-68. [link]
Projects on suicide
How do social contexts shape suicide risks? In turn, how do suicides alter social contexts? I address these classic questions in sociology by focusing on how individuals interact with their social contexts, and network effects. Attending to social mechanisms over mere correlates is a characteristic of both my research on suicide and autism. My collaborations with various multinational, interdisciplinary teams gave me access to data from Hong Kong [1, 2, 5, 6, 7, 8, 9, 10, 11, 15, 21] Taiwan , Mainland China [3, 4, 14], Sweden , U.K. , Australia  and globally .Click here for more info about my projects on suicide.
Projects on Autism
Why has the prevalence of autism increased so rapidly? Despite millions of research funding, we do not have a consensus on what drives the epidemic. My first contribution is to provide evidence that the diffusion of knowledge about autism through interpersonal networks has a substantial role. My second contribution is in linking demographic processes to the epidemiological patterns. My research on autism has won the Eliot Freidson Outstanding Publication Award of the American Sociological Association's Medical section. My papers appeared in the American Journal of Sociology, Demography, Sociological Methods and Research and other journals.
Click here for more info about my projects on autism.
Projects on Vaccination exemptions
An explanation of rising vaccine refusals is the spread of erroneous beliefs about vaccine safety—an unintended consequence of the autism epidemic, yet no large-scale study has examined its role in generating clusters of exemptions. Our results indicate that sorting along socioeconomic lines leaves important features of the spatial patterns unexplained. We find some evidence that the diffusion of vaccine safety concerns among racially homophilous networks contributes to the spatial clustering of exemptions.
The second part of this project is a large-scale simulation model of disease (e.g., measles) outbreak potential under different exemption regimes. Theoretical models suggest that spatial clusters of exemptions substantially increase chances of outbreaks. However, no study has looked into the risk level associated with the current spatial pattern. The stochastic nature of outbreaks makes simulation a valuable tool.
Current Courses by Term
Previous Courses by Term
Variable Topics Research Seminars: Sociology
Previous Courses by Course
Social Network Methods
2016 Spring Quarter
Intermediate Statistical Methods II
Advanced Honors Seminars