Lucy F. Robinson

Change point estimation in multi-subject fMRI studies

Most statistical analyses of fMRI data assume that the nature, timing and duration of the psychological processes being studied are known. However, in many areas of psychological inquiry, it is hard to specify this information a priori. Examples include studies of drug uptake, emotional states or experiments with a sustained stimulus. In this paper we assume that the timing of a subjects activation onset and duration are random variables drawn from unknown population distributions. We propose a technique for estimating these distributions assuming no functional form, and allowing for the possibility that some subjects may show no response. We illustrate how these distributions can be used to approximate the probability that a voxel/region is activated as a function of time. Further a procedure is discussed that uses a hidden Markov random field model to cluster voxels based on characteristics of their onset, duration, and anatomical location. These methods are applied to an fMRI study (n=24) of state anxiety, and are well suited for investigating individual differences in state-related changes in fMRI activity and other measures.

Dynamic functional connectivity using state-based dynamic community structure: Method and application to opioid analgesia

We present a new method, State-based Dynamic Community Structure, that detects time-dependent community structure in networks of brain regions. Most analyses of functional connectivity assume that network behavior is static in time, or differs between task conditions with known timing. Our goal is to determine whether brain network topology remains stationary over time, or if changes in network organization occur at unknown time points. Changes in network organization may be related to shifts in neurological state, such as those associated with learning, drug uptake or experimental conditions. Using a hidden Markov stochastic blockmodel, we define a time-dependent community structure. We apply this approach to data from a functional magnetic resonance imaging experiment examining how contextual factors influence drug-induced analgesia. Results reveal that networks involved in pain, working memory, and emotion show distinct profiles of time-varying connectivity.

The Temporal Instability of Resting State Network Connectivity in Intractable Epilepsy

Focal epilepsies, such as temporal lobe epilepsy (TLE), are known to disrupt network activity in areas outside the epileptogenic zone [Tracy et al., 2015]. We devised a measure of temporal instability of resting state functional connectivity (FC), capturing temporal variations of BOLD correlations between brain regions that is less confounded than the “sliding window” approach common in the literature.

Age- and gender-related changes in pediatric thoracic vertebral morphology

BACKGROUND CONTEXT Although it is well known that the growth of thoracic spine changes significantly with age, gender, and vertebral level in the skeletally normal pediatric population, there have been very few studies attempting to comprehensively quantify such variations. Biomechanical and computational models of the growing thoracic spine have provided insight into safety and efficacy of surgical and noninvasive treatments for spinal deformity. However, many of these models only consider growth of the vertebral body and pedicles and assume a consistent growth rate for these structures across thoracic levels. PURPOSE To enhance the understanding of age-, gender-, and level-related growth dynamics of the pediatric thoracic spine by comprehensively quantifying the thoracic vertebral morphology for subjects between 1 and 19 years. STUDY DESIGN A retrospective computed tomography (CT) image analysis study. METHODS Retrospectively obtained chest CT scans from 100 skeletally normal pediatric subjects (45 males and 55 females between the ages 1 and 19 years) were digitally reconstructed using medical imaging software. Surface point clouds of thoracic vertebrae were extracted and 26 vertebral geometry parameters were measured using 25 semiautomatically identified surface landmarks and anatomical slices from each thoracic vertebra (T1-T12). Data were assessed for normality, symmetry, and age-, gender-, and level-related differences in geometric measures and growth. Linear regression was performed to estimate of the rates of variation with age for each measurement. RESULTS Asymmetries (bilateral, superior-inferior, and anteroposterior) were observed in vertebral body heights, end plate widths and depths, and interfacet widths. Within genders, significant interlevel differences were observed for all geometric measures, and significant differences in the rates of growth were found across thoracic levels for most parameters. Significant differences were observed between genders for pedicle, spinous process, and facet measurements. Growth rates of the pedicles and vertebral bodies were also found to vary significantly between genders. CONCLUSIONS The rates of growth for most thoracic vertebral structures varied between genders and across vertebral levels. These growth rates followed trends similar to those of their associated vertebral dimensions and this indicates that, across levels and between genders, larger vertebral structures grow at faster rates, whereas smaller structures grow at a slower rate. Such level- and gender-specific information could be used to inform clinical decisions about spinal deformity treatment and adapted for use in biomechanical and computational modeling of thoracic growth and growth modulation.

Healthy and Unhealthy Food Prices across Neighborhoods and Their Association with Neighborhood Socioeconomic Status and Proportion Black/Hispanic

This paper evaluates variation in food prices within and between neighborhoods to improve our understanding of access to healthy foods in urbanized areas and potential economic incentives and barriers to consuming a higher-quality diet. Prices of a selection of healthier foods (dairy, fruit juice, and frozen vegetables) and unhealthy foods (soda, sweets, and salty snacks) were obtained from 1953 supermarkets across the USA during 2009–2012 and were linked to census block group socio-demographics. Analyses evaluated associations between neighborhood SES and proportion Black/Hispanic and the prices of healthier and unhealthy foods, and the relative price of healthier foods compared with unhealthy foods (healthy-to-unhealthy price ratio). Linear hierarchical regression models were used to explore geospatial variation and adjust for confounders. Overall, the price of healthier foods was nearly twice as high as the price of unhealthy foods (

Review of epidemiological studies of drinking-water turbidity in relation to acute gastrointestinal illness

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Neighbourhood variation in the price of soda relative to milk and its association with neighbourhood socio-economic status and race

0.298 per serving; healthy-to-unhealthy price ratio of 1.99). This trend was consistent across all neighborhood characteristics. After adjusting for covariates, no association was found between food prices (healthy, unhealthy, or the healthy-to-unhealthy ratio) and neighborhood SES. Similarly, there was no association between the proportion Black/Hispanic and healthier food price, a very small positive association with unhealthy price, and a modest negative association with the healthy-to-unhealthy ratio. No major differences were seen in food prices across levels of neighborhood SES and proportion Black/Hispanic; however, the price of healthier food was twice as expensive as unhealthy food per serving on average.

Work Characteristics Associated with Physical Functioning in Women

Background: Turbidity has been used as an indicator of microbiological contamination of drinking water in time-series studies attempting to discern the presence of waterborne gastrointestinal illness; however, the utility of turbidity as a proxy exposure measure has been questioned. Objectives: We conducted a review of epidemiological studies of the association between turbidity of drinking-water supplies and incidence of acute gastrointestinal illness (AGI), including a synthesis of the overall weight of evidence. Our goal was to evaluate the potential for causal inference from the studies. Methods: We identified 14 studies on the topic (distinct by region, time period and/or population). We evaluated each study with regard to modeling approaches, potential biases, and the strength of evidence. We also considered consistencies and differences in the collective results. Discussion: Positive associations between drinking-water turbidity and AGI incidence were found in different cities and time periods, and with both unfiltered and filtered supplies. There was some evidence for a stronger association at higher turbidity levels. The studies appeared to adequately adjust for confounding. There was fair consistency in the notable lags between turbidity measurement and AGI identification, which fell between 6 and 10 d in many studies. Conclusions: The observed associations suggest a detectable incidence of waterborne AGI from drinking water in the systems and time periods studied. However, some discrepant results indicate that the association may be context specific. Combining turbidity with seasonal and climatic factors, additional water quality measures, and treatment data may enhance predictive modeling in future studies. https://doi.org/10.1289/EHP1090

Neighborhood Prices of Healthier and Unhealthier Foods and Associations with Diet Quality: Evidence from the Multi-Ethnic Study of Atherosclerosis

OBJECTIVE Soda consumption is high in the USA, especially among minorities and individuals of lower socio-economic status (SES); this may be due to its affordable price in relation to healthier alternatives. The objective of the present study was to examine geospatial variation in price of milk and soda, and the price of milk relative to soda, by neighbourhood SES and proportion of Hispanic and black individuals. DESIGN Retailer soda and milk prices (n 2987; Information Resources, Inc. Academic Data Set 2004-2011) were linked to census block group sociodemographic characteristics (American Community Survey 2005-2009). Linear hierarchical regression models were used to adjust for confounders. SETTING Large chain supermarkets and superstores (n 1743) in forty-one states and 1694 block groups (USA). RESULTS For equivalent fluid ounces, price of soda on average was 62 % lower than milk (

Exploring Impacts of Taxes and Hospitality Bans on Cigarette Prices and Smoking Prevalence Using a Large Dataset of Cigarette Prices at Stores 2001–2011, USA

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