Sparse Bayesian mass-mapping with uncertainties: hypothesis testing of structure

A crucial aspect of mass-mapping, via weak lensing, is quantification of the uncertainty introduced during the reconstruction process. Properly accounting for these errors has been largely ignored to date. We present results from a new method that reconstructs maximum a posteriori (MAP) convergence maps by formulating an unconstrained Bayesian inference problem with Laplace-type $\ell_1$-norm sparsity-promoting priors, which we solve via convex optimization. Approaching mass-mapping in this manner allows us to exploit recent developments in probability concentration theory to infer theoretically conservative uncertainties for our MAP reconstructions, without relying on assumptions of Gaussianity. For the first time these methods allow us to perform hypothesis testing of structure, from which it is possible to distinguish between physical objects and artifacts of the reconstruction. Here we present this new formalism, demonstrate the method on illustrative examples, before applying the developed formalism to two observational datasets of the Abel-520 cluster. In our Bayesian framework it is found that neither Abel-520 dataset can conclusively determine the physicality of individual local massive substructure at significant confidence. However, in both cases the recovered MAP estimators are consistent with both sets of data

Critical Business? Critical Management Studies (CMS) perspectives on Corporate Social Responsibility (CSR)

Critical Management Studies (CMS) and Corporate Social Responsibility (CSR) are two theoretical traditions within the business school that are among the most critical of corporate management practices. While both are very distinct traditions, I argue that they have what amounts to certain shared goals to radically rethink and re-shape business and its “accepted utilitarian justification of business in terms of economic growth and material accumulation” (Crane 2000 p.674). One of the primary aims of this dissertation is to prove that the goals of CMS and CSR are proximate by detailing and defining both. Once this detailing of CSR and CMS is completed in Chapters 2 and 3, I shall question why there is little dialogue between these traditions, especially considering this when certain distilled characteristics of each tradition are viewed side by side in chapter 4. I shall then investigate the reasons for this gap in chapter 5. Additional aims in this dissertation include investigating and evaluating the differences in the CMS and CSR approaches to business, the corporation and management and the role these play in the world as currently configured. This dissertation presents the argument that in each tradition the role of business and particularly the assumptions about business can be categorised, evaluated and compared to each other despite both CMS and CSR being “essentially contested terms” (Moon, Matten & Crane 2005 p.434)

Mammography workstation design: effect on mammographer behaviour and the risk of musculoskeletal disorders

In the UK Breast Screening Programme there is a growing transition from film to digital mammography, and consequently a change in mammography workstation ergonomics. This paper investigates the effect of the change for radiologists including their comfort, likelihood of developing musculoskeletal disorders (MSD’s), and work practices. Three workstations types were investigated: one with all film mammograms; one with digital mammograms alongside film mammograms from the previous screening round, and one with digital mammograms alongside digitised film mammograms from the previous screening round. Mammographers were video-taped whilst conducting work sessions at each of the workstations. Event based Rapid Upper Limb Assessment (RULA) postural analysis showed no overall increase in MSD risk level in the switch from the film to digital workstation. Average number of visual glances at the prior mammograms per case measured by analysis of recorded video footage showed an increase if the prior mammograms were digitised, rather than displayed on a multi-viewer (p<.05). This finding has potential implications for mammographer performance in the transition to digital mammography in the UK

The human factors surrounding system change in breast cancer screening: a case study

Screening for breast cancer involves examination of mammograms. Conventional filmscreen mammography is being surpassed with the implementation of digital soft copy film reporting. However, little thought has been given to the human factors associated with the allied period of system changeover. This study considered the human factors implications with respect to comfort, performance and efficiency of work tasks. The purpose of this project was to examine the human factors issues surrounding the implementation of the new technology and prepare recommendations relevant to practitioners for improved implementation practice. A combination of techniques (expert walkthroughs, verbal protocol analysis, interviews, work station assessments) were applied to examine existing and revised working practices during mammography film reading. Eight Radiologists and Radiographer Advanced Practitioners within two Breast Screening Units participated to enable a thorough understanding to be gained of strategies adopted when using the different systems and the combination of systems. A variety of changes in working practices were recognised to have occurred with the new system (digital) implementation. There was an impact upon technique, comfort, performance and efficiency during digital soft copy reporting when viewing analogue priors. Subsequent recommendations for workstation design, working practices and training were produced to assist in improved implementation of digital processes in mammography. The project demonstrated that implementation of new technology needs to be thoroughly assessed to alleviate any potentially problematic human factors issues

Investigating the conformations of a family of [M2L3]4+ helicates using single crystal X-ray diffraction

We present five new dinuclear triple helicate compounds of types [Mn2L3](ClO4)4, [Co2L3](BF4)4, [Ni2L3](BF4)4, [Cu2L3](BF4)4, and [Zn2L3](BF4)4, where L is a previously reported semi-rigid ligand incorporating two α-diimine primary donor groups and two secondary 4-pyridyl donor groups. All complexes have been characterized in both solution and the solid state. Single crystal X-ray diffraction studies were used to probe the variation in the respective helical structures as the coordinated metal ion was altered, including the effect on the orientations of the secondary binding domains. The influence of the metal ion size, the spin state in the case of Fe(II), and the presence of Jahn-Teller distortions on the overall helical structure has been investigated. These results form a basis for the design and construction of new large metallosupramolecular architectures which manifest properties associated with the constituent helical metalloligand units

A method for exploratory repeated-measures analysis applied to a breast-cancer screening study

When a model may be fitted separately to each individual statistical unit, inspection of the point estimates may help the statistician to understand between-individual variability and to identify possible relationships. However, some information will be lost in such an approach because estimation uncertainty is disregarded. We present a comparative method for exploratory repeated-measures analysis to complement the point estimates that was motivated by and is demonstrated by analysis of data from the CADET II breast-cancer screening study. The approach helped to flag up some unusual reader behavior, to assess differences in performance, and to identify potential random-effects models for further analysis.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS481 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Influencing clinicians and healthcare managers: can ROC be more persuasive?

Receiver Operating Characteristic analysis provides a reliable and cost effective performance measurement tool, without using full clinical trials. However, when ROC analysis shows that performance is statistically superior in one condition than another it is difficult to relate this result to effects in practice, or even to determine whether it is clinically significant. In this paper we present two concurrent analyses: using ROC methods alongside single threshold recall rate data, and suggest that reporting both provides complimentary data. Four mammographers read 160 difficult cases (41% malignant) twice, with and without prior mammograms. Lesion location and probability of malignancy was reported for each case and analyzed using JAFROC. Concurrently each participant chose recall or return to screen for each case. JAFROC analysis showed that the presence of prior mammograms improved performance (p<.05). Single threshold data showed a trend towards a 26% increase in the number of false positive recalls without prior mammograms (p=.056). If this trend were present throughout the NHS Breast Screening Programme then discarding prior mammograms would correspond to an increase in recall rate from 4.6% to 5.3%, and 12,414 extra women recalled annually for assessment. Whilst ROC methods account for all possible thresholds of recall and have higher power, providing a single threshold example of false positive, false negative, and recall rates when reporting results could be more influential for clinicians. This paper discusses whether this is a useful additional method of presenting data, or whether it is misleading and inaccurat

Double reading in breast cancer screening : cohort evaluation in the CO-OPS trial

Purpose: To investigate the effect of double readings by a second radiologist on recall rates, cancer detection and characteristics of cancers detected in the National Health Service Breast Screening Program in England. Materials and Methods: In this retrospective analysis we evaluated 805,206 women through screening and diagnostic test results by extracting one year of routine data from 33 English breast screening centers. Centers used double reading of digital mammograms, with arbitration if there were discrepant reads. Information on reader decisions, with results of follow-up tests, were used to explore the effect of the second reader. The statistical tests used were the test for equality of proportions, the χ2 test for independence and the t-test. Results: The first reader recalled 4·76%, (38295/805206, 95% CI 4·71%-4·80%) of women. Two readers recalled 6·19% in total, (49857/805206, 95% CI 6·14%- 6·24%), but arbitration of discordant reads reduced recall rate to 4·08%, (32863/805206, 95% CI 4·04%-4·12%, p<0.001). 7055 cancers were detected of which 627 (8·89%, 95% CI 8·22%-9·55%, p<0.001) were detected by the second reader only. These additional cancers were more likely to be ductal carcinoma in situ, (30·5% (183/600) vs 22.0% (1344/6114), p<0.001); and additional invasive cancers were smaller (mean 14·2mm vs 16·7mm, p<0.001), had fewer involved nodes, and were likely to be lower grade. Conclusion: Double reading with arbitration reduces recall and increases cancer detection compared to single reading. Cancers detected only by the second reader were smaller, lower grade, and had less nodal involvement

Prevalence and predictors of kaposi sarcoma herpes virus seropositivity: a cross-sectional analysis of HIV-infected adults initiating ART in Johannesburg, South Africa

<p>Abstract</p> <p>Background</p> <p>Kaposi sarcoma (KS) is the most common AIDS-defining tumour in HIV-infected individuals in Africa. Kaposi sarcoma herpes virus (KSHV) infection precedes development of KS. KSHV co-infection may be associated with worse outcomes in HIV disease and elevated KSHV viral load may be an early marker for advanced HIV disease among untreated patients. We examined the prevalence of KSHV among adults initiating antiretroviral therapy (ART) and compared immunological, demographic and clinical factors between patients seropositive and seronegative for KSHV.</p> <p>Results</p> <p>We analyzed cross-sectional data collected from 404 HIV-infected treatment-naïve adults initiating ART at the Themba Lethu Clinic, Johannesburg, South Africa between November 2008 and March 2009. Subjects were screened at ART initiation for antibodies to KSHV lytic K8.1 and latent Orf73 antigens. Seropositivity to KSHV was defined as positive to either lytic KSHV K8.1 or latent KSHV Orf73 antibodies. KSHV viremia was determined by quantitative PCR and CD3, 4 and 8 lymphocyte counts were determined with flow cytometry. Of the 404 participants, 193 (48%) tested positive for KSHV at ART initiation; with 76 (39%) reactive to lytic K8.1, 35 (18%) to latent Orf73 and 82 (42%) to both. One individual presented with clinical KS at ART initiation. The KSHV infected group was similar to those without KSHV in terms of age, race, gender, ethnicity, smoking and alcohol use. KSHV infected individuals presented with slightly higher median CD3 (817 vs. 726 cells/mm³) and CD4 (90 vs. 80 cells/mm³) counts than KSHV negative subjects. We found no associations between KSHV seropositivity and body mass index, tuberculosis status, WHO stage, HIV RNA levels, full blood count or liver function tests at initiation. Those with detectable KSHV viremia (n = 19), however, appeared to present with signs of more advanced HIV disease including anemia and WHO stage 3 or 4 defining conditions compared to those in whom the virus was undetectable.</p> <p>Conclusions</p> <p>We demonstrate a high prevalence of KSHV among HIV-infected adults initiating ART in a large urban public-sector HIV clinic. KSHV viremia but not KSHV seropositivity may be associated with markers of advanced HIV disease.</p