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New paper on cyclic network organisms describing how growth produces evolutionary pressures towards the emergence of cellular heterogeneity

“Attractor-based obstructions to growth in homogenous cyclic Boolean automata.”Journal of Computer Science and System Biology 8(6): 341-353.
Bilal Khan, Yuri Kantor, Kirk Dombrowski,

We consider a synchronous Boolean organism consisting of N cells arranged in a circle, where each cell initially takes on an independently chosen Boolean value. During the lifetime of the organism, each cell updates its own value by responding to the presence (or absence) of diversity amongst its two neighbours’ values. We show that if all cells eventually take a value of 0 (irrespective of their initial values) then the organism necessarily has a cell count that is a power of 2. In addition, the converse is also proved: if the number of cells in the organism is a proper power of 2, then no matter what the initial values of the cells are, eventually all cells take on a value of 0 and then cease to change further. We argue that such an absence of structure in the dynamical properties of the organism implies a lack of adaptiveness, and so is evolutionarily disadvantageous. It follows that as the organism doubles in size (say from m to 2m) it will necessarily encounter an intermediate size that is a proper power of 2, and suffers from low adaptiveness. Finally we show, through computational experiments, that one way an organism can grow to more than twice its size and still avoid passing through intermediate sizes that lack structural dynamics, is for the organism to depart from assumptions of homogeneity at the cellular level.


New paper exploring the non-injection drug use among MSM and its role in Hepatitis-C incidence

“Hepatitis C. Virus Incidence among HIV+ Men Who Have Sex with Men: The Role of Non-Injection Drug Use.” Drug and Alcohol Dependence 146: e118-e201.
H. Hagan, J. Nuerer, A. E. Jordan, D. C. Des Jarlais, J. Wu, K. Dombrowski, B. Khan, S. Braithwaite, J. Kessler.

Outbreaks of hepatitis C virus (HCV) infection have been reported in HIV-positive men who have sex with men (MSM) in North America, Europe and Asia. Transmission is believed to be the result of exposure to blood during sexual contact. In those infected with HIV, acute HCV infection is more likely to become chronic, treatment for both HIV and HCV is more complicated and HCV disease progression may be accelerated. There is a need for systematic reviews and meta-analyses to synthesize the epidemiology, prevention and methods to control HCV infection in this population.
Eligible studies will include quantitative empirical data related to sexual transmission of HCV in HIV-positive MSM, including data describing incidence or prevalence, and associations between risk factors or interventions and the occurrence or progression of HCV disease. Care will be taken to ensure that HCV transmission related to injection drug use is excluded from the incidence estimates. Scientific databases will be searched using a comprehensive search strategy. Proceedings of scientific conferences, reference lists and personal files will also be searched. Quality ratings will be assigned to each eligible report using the Newcastle–Ottawa scale. Pooled estimates of incidence rates and measures of association will be calculated using random effects models. Heterogeneity will be assessed at each stage of data synthesis.
HIV-positive MSM are a key HCV-affected population in the US and other high-income countries. This review seeks to identify modifiable risk factors and settings that will be the target of interventions, and will consider how to constitute a portfolio of interventions to deliver the greatest health benefit. This question must be considered in relation to the magnitude of HCV infection and its consequences in other key affected populations, namely, young prescription opioid users who have transitioned to illicit opiate injection, and older injection drug users among whom HCV prevalence and incidence are extremely high. This review is part of a series of systematic reviews and meta-analyses that will synthesize the evidence across all these population groups and develop recommendations and decision tools to guide public health resource allocation.


New paper on Hispanic immigrant victims of violence seeks to determine predictors of police reporting using a network-centric approach

“Predictors of police reporting among Hispanic immigrant victims of violence.” Race and Justice 5(3): 235-258.  2015
Dane Hautala, Kirk Dombrowski, and Anthony Marcus.

The purpose of this study was to examine predictors of police reporting among Hispanic immigrant victims of violence. A sample of 127 Hispanic immigrants was generated through a chain-referral procedure in the city of Hempstead, New York. Participants were asked about their most recent victimization experiences, and detailed information was collected on up to three incidents. The analyses were based on a total of 214 separate victimization incidents, one third of which were reported to the police. Logistic regression analyses indicated that serious injury, multiple-victim incidents, and perceptions of discrimination increase the odds of a police report. Moreover, incidents involving a Black primary assailant were less likely to be reported to the police than incidents involving an assailant perceived to be of Hispanic origin. Supplementary analyses suggested that this latter relationship may be contingent upon the type of crime and the victim’s relationship with the assailant. At the policy level, these findings call into question assumptions about very recent immigrants being too socially isolated and distrustful of law enforcement to sustain robust reporting levels, as well as pointing to encouraging possibilities for productive engagement between police and Hispanic immigrant populations.

New paper describing network-centric study of sexual violence in the Congo

“Respondent-driven sampling to recruit survivors of sexual violence: a methodological assessment” American Journal of Epidemiology 180(5):536-544.

Ashley Greiner, Katherine Albutt, Shada Rouhani, Jennifer Scott, Kirk Dombrowski, Susan Bartels

Sexual violence is pervasive in eastern Democratic Republic of Congo (DRC). Survivors of sexual violence encounter numerous challenges, and women with a sexual violence–related pregnancy (SVRP) face even more complex sequelae. Because of the stigma associated with SVRP, there is no conventional sampling frame and, therefore, a paucity of research on SVRP outcomes. Respondent-driven sampling (RDS), used to study this “hidden” population, uses a peer recruitment sampling system that maintains strict participant privacy and controls and tracks recruitment. If RDS assumptions are met and the sample attains equilibrium, sample weights to correct for biases associated with traditional chain referral sampling can be calculated. Questionnaires were administered to female participants who were raising a child from a SVRP and/or who terminated a SVRP. A total of 852 participants were recruited from October 9, 2012, to November 7, 2012. There was rapid recruitment, and there were long referral chains. The majority of the variables reached equilibrium; thus, trends established in the sample population reflected the target population’s trends. To our knowledge, this is the first study to use RDS to study outcomes of sexual violence. RDS was successfully applied to this population and context and should be considered as a sampling methodology in future sexual violence research.

New paper on a network study of Nain Labrador and on the many Social Divisions discovered therein

“Sampling Social Divisions in a Rural Inuit Community.” Identities 21 (2): 134-151.
Kirk Dombrowski, Bilal Khan, Joshua Moses, Emily Channell, and Ric Curtis

This paper describes results from a network survey of Nain – a predominantly Inuit community of ~1200 people located on the northern coast of Labrador. As part of a larger social network research project, we used peer-referral sampling to recruit 330 residents for interviews about food sharing, housing, public health and community traditions. The peer-referral chains were analysed statistically to determine the presence and absence of social divisions in the community. The results of these analyses show that ethnic identification, relocation status and household income were the most significant social divisions in the community, while gender, education level and employment status show little or no effect on patterns of between-group interconnection. We argue that statistical patterns in the presence (and absence) of intergroup links offer novel ways to examine the interrelationship between recent economic development and the historical disruptions caused by Inuit community relocations in the 1950s.