The Examination of Nonparametric Person-Fit Statistics as Appropriate Measures of Response Bias in Ordered Polytomous Items

Survey research is ubiquitous within the social sciences; however, surveys are vulnerable to response biases. Response biases introduce construct-irrelevant variance into survey responses, which degrades the accuracy of conclusions drawn through the use of surveys. Nonparametric person-fit statistics have been shown to accurately identify response biases in dichotomous response data but are not well studied in polytomous response data. This study examines the accuracy of nonparametric person-fit statistics in polytomous response data. A 6 x 4 x 4 x 2 simulation study was conducted, with type of aberrancy (6), number of response options (4), dimensionality (4), and test length (2) as factors. The sensitivity, specificity, positive predictive value, and negative predictive value for U3, the normed number of Guttman errors, and HTi were calculated using a bootstrapped cutoff. Findings indicate that these person-fit statistics with a conservative cutoff had excellent specificity but poor sensitivity. Advisor: Kurt F. Geisinge

Examining Doctoral Attrition: A Self-Determination Theory Approach

Doctoral student attrition is a troubling and costly phenomenon. Alarmingly, 40-60% of doctoral students will not complete their Ph.D. Several explanations for this high and persistent attrition rate have been discussed in the extant literature, including questioning the quality, mental health, and motivation of doctoral students. However, stricter admission standards and empirical evidence provide little support that any one of these current explanations is adequate on its own. Empirical clues suggest that Self-Determination Theory may be useful in trying to understand the doctoral attrition phenomenon. Self- Determination Theory is presented and used as a framework to identify potential causes and barriers in the doctoral student experience that may lead to drop out. These issues are discussed and preliminary suggestions for potential strategies to rectify these issues are given

Examining Doctoral Attrition: A Self-Determination Theory Approach

Doctoral student attrition is a troubling and costly phenomenon. Alarmingly, 40-60% of doctoral students will not complete their Ph.D. Several explanations for this high and persistent attrition rate have been discussed in the extant literature, including questioning the quality, mental health, and motivation of doctoral students. However, stricter admission standards and empirical evidence provide little support that any one of these current explanations is adequate on its own. Empirical clues suggest that Self-Determination Theory may be useful in trying to understand the doctoral attrition phenomenon. Self- Determination Theory is presented and used as a framework to identify potential causes and barriers in the doctoral student experience that may lead to drop out. These issues are discussed and preliminary suggestions for potential strategies to rectify these issues are given

A High Power Hydrogen Target for Parity Violation Experiments

Parity-violating electron scattering measurements on hydrogen and deuterium, such as those underway at the Bates and CEBAF laboratories, require luminosities exceeding $10^{38}$cm$^{-2}$s$^{-1}$, resulting in large beam power deposition into cryogenic liquid. Such targets must be able to absorb 500 watts or more with minimal change in target density. A 40~cm long liquid hydrogen target, designed to absorb 500~watts of beam power without boiling, has been developed for the SAMPLE experiment at Bates. In recent tests with 40~$\mu$A of incident beam, no evidence was seen for density fluctuations in the target, at a sensitivity level of better than 1\%. A summary of the target design and operational experience will be presented.Comment: 13 pages, 9 postscript figure

The human homologue of unc-93 maps to chromosome 6q27 – characterisation and analysis in sporadic epithelial ovarian cancer

BACKGROUND: In sporadic ovarian cancer, we have previously reported allele loss at D6S193 (62%) on chromosome 6q27, which suggested the presence of a putative tumour suppressor gene. Based on our data and that from another group, the minimal region of allele loss was between D6S264 and D6S149 (7.4 cM). To identify the putative tumour suppressor gene, we established a physical map initially with YACs and subsequently with PACs/BACs from D6S264 to D6S149. To accelerate the identification of genes, we sequenced the entire contig of approximately 1.1 Mb. Seven genes were identified within the region of allele loss between D6S264 and D6S149. RESULTS: The human homologue of unc-93 (UNC93A) in C. elegans was identified to be within the interval of allele loss centromeric to D6S149. This gene is 24.5 kb and comprises of 8 exons. There are two transcripts with the shorter one due to splicing out of exon 4. It is expressed in testis, small intestine, spleen, prostate, and ovary. In a panel of 8 ovarian cancer cell lines, UNC93A expression was detected by RT-PCR which identified the two transcripts in 2/8 cell lines. The entire coding sequence was examined for mutations in a panel of ovarian tumours and ovarian cancer cell lines. Mutations were identified in exons 1, 3, 4, 5, 6 and 8. Only 3 mutations were identified specifically in the tumour. These included a c.452G>A (W151X) mutation in exon 3, c.676C>T (R226X) in exon 5 and c.1225G>A(V409I) mutation in exon 8. However, the mutations in exon 3 and 5 were also present in 6% and 2% of the normal population respectively. The UNC93A cDNA was shown to express at the cell membrane and encodes for a protein of 60 kDa. CONCLUSIONS: These results suggest that no evidence for UNC93A as a tumour suppressor gene in sporadic ovarian cancer has been identified and further research is required to evaluate its normal function and role in the pathogenesis of ovarian cancer

The Cost-Effectiveness of Early Access to HIV Services and Starting cART in the UK 1996–2008

To calculate use, cost and cost-effectiveness of people living with HIV (PLHIV) starting routine treatment and care before starting combination antiretroviral therapy (cART) and PLHIV starting first-line 2NRTIs+NNRTI or 2NRTIs+PI(boosted), comparing PLHIV with CD4≤200 cells/mm3 and CD4>200 cells/mm3. Few studies have calculated the use, cost and cost-effectiveness of routine treatment and care before starting cART and starting cART above and below CD4 200 cells/mm3.Use, costs and cost-effectiveness were calculated for PLHIV in routine pre-cART and starting first-line cART, comparing CD4≤200 cells/mm3 with CD4>200 cells/mm3 (2008 UK prices).cART naïve patients CD4≤200 cells/mm3 had an annual cost of £6,407 (95%CI £6,382 to £6,425) PPY compared with £2,758 (95%CI £2,752 to £2,761) PPY for those with CD4>200 cells/mm3; cost per life year gained of pre-cART treatment and care for those with CD4>200 cells/mm3 was £1,776 (cost-saving to £2,752). Annual cost for starting 2NRTIs+NNRTI or 2NRTIs+PI(boosted) with CD4≤200 cells/mm3 was £12,812 (95%CI £12,685-£12,937) compared with £10,478 (95%CI £10,376-£10,581) for PLHIV with CD4>200 cells/mm3. Cost per additional life-year gained on first-line therapy for those with CD4>200 cells/mm3 was £4639 (£3,967 to £2,960).PLHIV starting to use HIV services before CD4≤200 cells/mm3 is cost-effective and enables them to be monitored so they start cART with a CD4>200 cells/mm3, which results in better outcomes and is cost-effective. However, 25% of PLHIV accessing services continue to present with CD4≤200 cells/mm3. This highlights the need to investigate the cost-effectiveness of testing and early treatment programs for key populations in the UK

A sentence completion procedure as an alternative to the Autobiographical Memory Test for assessing overgeneral memory in non-clinical populations

Overgeneral memory (OGM) has been proposed as a vulnerability factor for depression (Williams et al., 2007) or depressive reactivity to stressful life-events (e.g., Gibbs & Rude, 2004). Traditionally, a cue word procedure known as the Autobiographical Memory Test (AMT; Williams & Broadbent, 1986) is used to assess OGM. Although frequently and validly used in clinical populations, there is evidence suggesting that the AMT is insufficiently sensitive to measure OGM in non-clinical groups. Study 1 evaluated the usefulness of a sentence completion method to assess OGM in non-clinical groups, as an alternative to the AMT. Participants were 197 students who completed the AMT, the Sentence Completion for Events from the Past Test (SCEPT), a depression measure, and visual analogue scales assessing ruminative thinking. Results showed that the mean proportion of overgeneral responses was markedly higher for the SCEPT than for the standard AMT. Also, overgeneral responding on the SCEPT was positively associated to depression scores and depressive rumination scores, whereas overgeneral responding on the AMT was not. Results suggest that the SCEPT, relative to the AMT, is a more sensitive instrument to measure OGM, at least in non-clinical populations. Study 2 further showed that this enhanced sensitivity is most likely due to the omission of the instruction to be specific rather than to the SCEPT's sentence completion format (as opposed to free recall to cue words)

Galaxy Zoo: morphological classification of galaxy images from the Illustris simulation

Modern large-scale cosmological simulations model the universe with increasing sophistication and at higher spatial and temporal resolutions. These ongoing enhancements permit increasingly detailed comparisons between the simulation outputs and real observational data. Recent projects such as Illustris are capable of producing simulated images that are designed to be comparable to those obtained from local surveys. This paper tests the degree to which Illustris achieves this goal across a diverse population of galaxies using visual morphologies derived from Galaxy Zoo citizen scientists. Morphological classifications provided by these volunteers for simulated galaxies are compared with similar data for a compatible sample of images drawn from the Sloan Digital Sky Survey (SDSS) Legacy Survey. This paper investigates how simple morphological characterization by human volunteers asked to distinguish smooth from featured systems differs between simulated and real galaxy images. Significant differences are identified, which are most likely due to the limited resolution of the simulation, but which could be revealing real differences in the dynamical evolution of populations of galaxies in the real and model universes. Specifically, for stellar masses, a substantially larger proportion of Illustris galaxies that exhibit disk-like morphology or visible substructure, relative to their SDSS counterparts. Toward higher masses, the visual morphologies for simulated and observed galaxies converge and exhibit similar distributions. The stellar mass threshold indicated by this divergent behavior confirms recent works using parametric measures of morphology from Illustris simulated images. When , the Illustris data set contains substantially fewer galaxies that classifiers regard as unambiguously featured. In combination, these results suggest that comparison between the detailed properties of observed and simulated galaxies, even when limited to reasonably massive systems, may be misleading