On nonlinear structural equation analysis

Applied interest in considering nonlinear structural equation models has increased in recent years. This dissertation deals with fitting a nonlinear structural equation model consisting of two parts: a linear measurement model relating observed variables to unobserved concepts or factors, and a nonlinear structural model where one particular factor is a polynomial in other factors. Two new statistical procedures are developed, and their justification and usefulness are discussed;The first procedure follows the ad-hoc approach that has been used in some applications. Some statistical limitation is revealed for the existing approach, and a new general method called the generalized appended product indicator (GAPI) procedure is introduced. The GAPI procedure uses products of observed variables as indicators for nonlinear terms in the structural model. Then, a proper model is fitted to the combined set of indicators by minimizing a discrepancy function. The resulting estimator is consistent without assuming any distributional form for the underlying factors or errors. Issues regarding identifiability and standard error estimation are discussed. A simulation study addresses statistical issues including comparisons of discrepancy functions and the choice of appended product indicators. One advantage of the GAPI procedure is that it can be implemented using existing software;An alternative approach developed here is the two-stage method of moment (2SMM) procedure which is applicable for virtually any polynomial structural modeling problem. In the first stage, the measurement model is fitted, and factor score estimates are obtained along with estimated moments of the measurement error associated with the factor score estimation. In the second stage, the nonlinear structural model parameter is estimated based on the factor score estimates by applying a method of moments procedure similar to that used in the errors-in-variables regression. The asymptotic properties of the 2SMM estimator are derived, and a modified estimator with better small sample properties is introduced. The asymptotic covariance matrix of the estimator which incorporates variability from the first stage estimation is presented. Various simulation studies are presented showing the superiority of 2SMM over other methods. An example from a substance-abuse prevention study is also discussed

This is only Temporary

This is only Temporary examines my personal history of homes as reimagined spaces. The series of prints in the exhibition depicts reconstructed memories of houses. These visual narratives give context to the installation constructed from handmade paper and raw materials. The framework is reminiscent of housing plans that converge into a labyrinth. Participants actively engage the space, navigating the confined structure. A playful nature runs throughout the prints and installation reflecting upon reinterpreted memories within transitional spaces

Evolution of AGN Space Densities and the FR Dichotomy

We focus on a comparison of the space densities of FRI and FRII extended radio sources at different epochs, and find that FRI and FRII sources show similar space density enhancements in various redshift ranges, possibly implying a common evolution.Comment: IAU Symposium 267 Proceeding - 1 pag

Investigating the requirement for dual cell co-culture platforms in creating regenerative cell therapies for CNS injury

Injuries to the central nervous system (CNS) can be devastating. CNS injuries include those to the spinal cord, where there can be a complete loss of function below the point of injury. Spinal cord injury impacts up to 500,000 people worldwide every year and where function is lost, quality of life can be severely limited. Olfactory ensheathing cells (OECs) are a candidate cell therapy for spinal cord injury as they can promote neuronal survival and facilitate regeneration of severed axons. Despite their unique properties, OECs are very challenging cells to work with because they are difficult to isolate, difficult to sustain in culture for prolonged periods and there is still controversy around how to characterize their identity and potency. The overall aim of this project is to identify methods to enhance the survival, growth and function of OECs. It has been reported that for OECs to be truly functional they require interaction with fibroblasts. Therefore, we sought to investigate whether it is necessary to use fibroblasts as a feeder layer to support OECs via physical cell-cell contact, or whether paracrine soluble factors in the conditioned media from fibroblasts would provide the trophic support necessary to enhance OEC survival and growth. A human mucosal fibroblast cell line was used as a feeder layer. Primary rat OECs were cultured for 14 days on the feeder layer or control substrate (laminin-coated dishes). After 14 days, the morphology of cells was assessed and an algorithm generated using ImageJ was used to ascribe a mathematical value to OEC morphology to determine whether a correlation of morphology to expression of markers could be made. Cells cultured on feeders adopted a more spindle-like appearance compared with cells cultured on laminin, which adopted an enlarged morphology. The algorithm was used to analyse the circularity of cells that labelled positive for candidate identity marker S100b. It was found that cells cultured on feeders had a lower circularity, and therefore more elongated shape compared to those cultured on laminin (p=0.037). Additionally, a significant increase in p75NTR expression (a second candidate OEC marker) was observed (p=0.01) on feeders. To further investigate the relationship between the OECs and the feeders, cells were cultured in the presence of conditioned media from the fibroblasts. When cells were cultured in conditioned media there was a significant (p=0.002) upregulation of Thy1, an undesirable marker, and the significance of this will be investigated further with work underway to compare different feeder types and their impact on marker expression

Household income differences in food sources and food items purchased

<p>Abstract</p> <p>Background</p> <p>The present study examined income-related household food purchases among a sample of 90 households from the community.</p> <p>Methods</p> <p>Annotated food purchase receipts were collected for a four-week period by the primary household shopper. Receipt food source and foods items were classified into specific categories, and food quantities in ounces were recorded by research staff. For home sources, a limited number of food/beverage categories were recorded. For eating out sources, all food/beverage items were recorded. Median monthly per person dollars spent and per person ounces purchased were computed. Food sources and food categories were examined by household income tertile.</p> <p>Subjects and Setting</p> <p>A community-based sample of 90 households.</p> <p>Results</p> <p>Higher income households spent significantly more dollars per person per month from both home and eating out sources compared with lower income households ($163 versus$100, p < .001). Compared with lower income households, higher income households spent significantly more home source dollars on both fruits/vegetables (21.5 versus 10.2, p < .001) and sweets/snacks (17.3 versus 8.3, p < .001), but did not differ on home dollars spent on sugar sweetened beverages (2.0 versus 1.7, p < .46). The proportion of home beverages that were sugar sweetened beverages was significantly higher among lower income households (45% versus 26%, p < .01). Within eating out sources, lower income households spent a significantly greater percent of dollars per person at carry out places (54% versus 37%, p < .01). No income differences were observed for dollars spent at discount grocery stores, small grocery stores or convenience stores.</p> <p>Conclusions</p> <p>Higher income households spent more money on both healthy and less healthy foods from a wide range of sources. Lower income households spent a larger proportion of their eating out dollars at carry out places, and a larger proportion of their home beverage purchases were sugar sweetened beverages.</p

Assessing dimensionality in dichotomous items when many subjects have all-zero responses: an example from psychiatry and a solution using mixture models

Common methods for determining the number of latent dimensions underlying an item set include eigenvalue analysis and examination of fit statistics for factor analysis models with varying number of factors. Given a set of dichotomous items, the authors demonstrate that these empirical assessments of dimensionality often incorrectly estimate the number of dimensions when there is a preponderance of individuals in the sample with all-zeros as their responses, for example, not endorsing any symptoms on a health battery. Simulated data experiments are conducted to demonstrate when each of several common diagnostics of dimensionality can be expected to under- or over-estimate the true dimensionality of the underlying latent variable. An example is shown from psychiatry assessing the dimensionality of a social anxiety disorder battery where 1, 2, 3, or more factors are identified, depending on the method of dimensionality assessment. An all-zero inflated exploratory factor analysis model (AZ-EFA) is introduced for assessing the dimensionality of the underlying subgroup corresponding to those possessing the measurable trait. The AZ-EFA approach is demonstrated using simulation experiments and an example measuring social anxiety disorder from a large nationally representative survey. Implications of the findings are discussed, in particular, regarding the potential for different findings in community versus patient populations

Gender differences in treatment adherence among youth with cystic fibrosis: Development of a new questionnaire

AbstractBackgroundSome prior studies have reported that girls with cystic fibrosis (CF) experience higher morbidity and mortality compared to boys. In this study, the authors compared boys' and girls' perceptions of disease-related strains and resources associated with living with CF, and the relationship of these factors to CF treatment feelings and behaviors.MethodsAll 10–21 year olds with CF at the Minnesota Cystic Fibrosis Center were invited by mail to complete a new self-report survey (Living with CF Questionnaire — LCFQ). Of these 177 youth, 58% (49 boys and 54 girls) returned surveys.ResultsExploratory and confirmatory factor analyses revealed nine factors in the LCFQ. Partial support was found for hypothesized gender differences in these factors. Compared to boys, girls reported significantly more illness-related strains and worries, including emotional strains, greater treatment discouragement, lower self-esteem, and lower adherence to some aspects of the CF treatment regimen (coughing, eating high-fat foods, taking meds/pills).ConclusionsLiving with CF appears to have a greater emotional impact on adolescent girls compared to boys. These gender differences may contribute to the poorer pulmonary function observed among girls with cystic fibrosis during the adolescent years

Analysis of strain IRB-1 as a potential candidate for uranium bioremediation in an extreme environment [abstract]

Abstract only availableSoap Lake, a halo-alkaline meromictic lake, in central Washington State is host to a variety of microorganisms capable of growth in these extreme conditions. These microorganisms have been shown to play a central role in geochemical cycling of the lake. In particular, an isolate designated strain IRB-1, a sulfur- and iron-reducing obligately anaerobic bacterium, exhibits qualities that may be beneficial for bioremediation in highly alkaline and saline environments found in contaminated industrial sites and some water systems. Strain IRB-1 was cultivated in batch cultures under anaerobic conditions in a medium that simulated site geochemistry. The original cultures were grow at a pH of 9.5, 1.2M NaCl, 60mM lactate, and 2mM Fe(III)-citrate as an electron acceptor. In all cultures growth was observed through increased protein biomass and reduction of Fe(III) over time. Scanning electron microscopy was used to analyze planktonic and biofilm cultures of IRB-1. The electron micrographs depicted the presence of extracellular appendages extending into the substrate and creating cell to cell connections. The original medium was modified by altering the terminal electron acceptor to 50mM of either sulfate, sulfite, thiosulfate, or elemental sulfur to determine the metabolic flexibility of the organism. Growth was observed only in cultures containing sulfur and thiosulfate and was confirmed over the span of several subcultures. We infer from the ability of IRB-1 to reduce Fe(III), thiosulfate, and sulfur that it may also have the ability to reduce heavy metals, specifically U(VI). Experiments are currently underway to determine the capacity of IRB-1 to grow in the presence of and/or reduce 2mM U(VI) as the sole terminal electron acceptor. Should this bacterium have the capability to reduce U(VI) and other heavy metals, it would become a candidate for bioremediation efforts in saline and highly alkaline environments where organisms traditionally employed for bioremediation can not be used.Department of Energy Genomics: Genomes to Life Progra