Clustering student skill set profiles in a unit hypercube using mixtures of multivariate betas

<br>This paper presents a finite mixture of multivariate betas as a new model-based clustering method tailored to applications where the feature space is constrained to the unit hypercube. The mixture component densities are taken to be conditionally independent, univariate unimodal beta densities (from the subclass of reparameterized beta densities given by Bagnato and Punzo 2013). The EM algorithm used to fit this mixture is discussed in detail, and results from both this beta mixture model and the more standard Gaussian model-based clustering are presented for simulated skill mastery data from a common cognitive diagnosis model and for real data from the Assistment System online mathematics tutor (Feng et al 2009). The multivariate beta mixture appears to outperform the standard Gaussian model-based clustering approach, as would be expected on the constrained space. Fewer components are selected (by BIC-ICL) in the beta mixture than in the Gaussian mixture, and the resulting clusters seem more reasonable and interpretable.</br> <br>This article is in technical report form, the final publication is available at http://www.springerlink.com/openurl.asp?genre=article &id=doi:10.1007/s11634-013-0149-z</br&gt

“Transfer Talk” in Talk about Writing in Progress: Two Propositions about Transfer of Learning

This article tracks the emergence of the concept of “transfer talk”—a concept distinct from transfer of learning—and teases out the implications of transfer talk for theories of transfer of learning. The concept of transfer talk was developed through a systematic examination of 30 writing center transcripts and is defined as “the talk through which individuals make visible their prior learning (in this case, about writing) or try to access the prior learning of someone else.” In addition to including a taxonomy of transfer talk and analysis of which types occur most often in this set of conferences, this article advances two propositions about the nature of transfer of learning: (1) transfer of learning may have an important social, even collaborative, component and (2) although meta-awareness about writing has long been recognized as valuable for transfer of learning, more automatized knowledge may play an important role as well

Discovery of Precursor LBV Outbursts in Two Recent Optical Transients: The Fitfully Variable Missing Links UGC 2773-OT and SN 2009ip

We present progenitor-star detections, light curves, and optical spectra of SN2009ip and the 2009 optical transient in UGC2773 (U2773-OT), which were not genuine SNe. Precursor variability in the decade before outburst indicates that both of the progenitor stars were LBVs. Their pre-outburst light curves resemble the S Doradus phases that preceded giant eruptions of eta Carinae and SN1954J (V12 in NGC2403), with intermediate progenitor luminosities. HST detections a decade before discovery indicate that the SN2009ip and U2773-OT progenitors were supergiants with likely initial masses of 50-80 Msun and \ga20 Msun, respectively. Both outbursts had spectra befitting known LBVs, although in different physical states. SN 2009ip exhibited a hot LBV spectrum with characteristic speeds of 550 km/s, plus faster material up to 5000 km/s, resembling the slow Homunculus and fast blast wave of eta Carinae. U2773-OT shows a forest of narrow absorption and emission lines comparable to that of S Dor in its cool state, plus [CaII] emission and an IR excess indicative of dust, similar to SN2008S and N300-OT. [CaII] emission is probably tied to a dusty pre-outburst environment, and not the outburst mechanism. SN2009ip and U2773-OT may provide a critical link between historical LBV eruptions, while U2773-OT may provide a link between LBVs and SN2008S and N300-OT. Future searches will uncover more examples of precursor LBV variability of this kind, providing key clues that may help unravel the instability driving LBVs.Comment: 18 pages, 13 Figures, accepted AJ. added significant material while revising after referee repor

sARI: a soft agreement measure for class partitions incorporating assignment probabilities

Agreement indices are commonly used to summarize the performance of both classification and clustering methods. The easy interpretation/intuition and desirable properties that result from the Rand and adjusted Rand indices, has led to their popularity over other available indices. While more algorithmic clustering approaches like k-means and hierarchical clustering produce hard partition assignments (assigning observations to a single cluster), other techniques like model-based clustering include information about the certainty of allocation of objects through class membership probabilities (soft partitions). To assess performance using traditional indices, e.g., the adjusted Rand index (ARI), the soft partition is mapped to a hard set of assignments, which commonly overstates the certainty of correct assignments. This paper proposes an extension of the ARI, the soft adjusted Rand index (sARI), with similar intuition and interpretation but also incorporating information from one or two soft partitions. It can be used in conjunction with the ARI, comparing the similarities of hard to soft, or soft to soft partitions to the similarities of the mapped hard partitions. Simulation study results support the intuition that in general, mapping to hard partitions tends to increase the measure of similarity between partitions. In applications, the sARI more accurately reflects the cluster boundary overlap commonly seen in real data

Complex PrEP: the factors requiring consultant-led review of PrEP users

INTRODUCTION: HIV-1 pre-exposure prophylaxis (PrEP) has been available in England since March 2020 on the National Health Service using generic emtricitabine and tenofovir disoproxil. 56 Dean Street (56DS) provided PrEP through (1) additional private care from September 2015, estimated to be providing 11% of England's PrEP in 2019; and (2) the IMPACT trial, as well as monitoring those self-sourcing PrEP. Providing PrEP at scale through a nurse-led service required a safety net for complex individuals. 56DS introduced a consultant-led PrEP outpatient service, the PrEP review clinic, in January 2018 and we report the outcomes of this service. METHODS: We present a retrospective case note review of the PrEP review clinic with descriptive outcomes from 26 January 2018 to 20 December 2019. Reason for referral, demographics, PrEP management and PrEP discontinuations were recorded. RESULTS: 13 980 unique users accessed PrEP from 56DS during the two year evaluation period. 220 individuals were seen in the PrEP review clinic. Majority of patients were referred for renal issues (114 of 220, 51.8%), followed by side effects (59 of 220, 26.8%) and comorbidities (38 of 220, 17.2%). Of those with renal issues, 89 (out of 114, 78.1%) users were referred for an abnormal estimated glomerular filtration rate (eGFR). 35 (out of 114, 30.7%) PrEP users had an eGFR between 45 and 59 mL/min/1.73 m2, of whom 2 (5.7%) discontinued PrEP. Majority of users were advised to stop supplements±switch to event-based dosing (24 of 35, 68.6%). Ten PrEP users were referred with an eGFR between 30 and 44 mL/min/1.73 m2; 4 (40%) stopped or did not start PrEP and 6 (60%) were asked to stop supplements±switch to event-based dosing. DISCUSSION: A small proportion of PrEP users have complex PrEP issues. Methods to manage renal dysfunction with PrEP included stopping supplements and switching to event-based dosing. Those with side effects were managed with an array of options, with only modest effectiveness. Other PrEP options are needed to support those with toxicities or intolerances

Modelling a socialised chatbot using trust development in children: Lessons learnt from Tay

In 2016 Microsoft released Tay.ai to the Twittersphere, a conversational chatbot that was intended to act like a millennial girl. However, they ended up taking Tay's account down in less than 24 h because Tay had learnt to tweet racist and sexist statements from its online interactions. Taking inspiration from the theory of morality as cooperation, and the place of trust in the developmental psychology of socialisation, we offer a multidisciplinary and pragmatic approach to build on the lessons learnt from Tay's experiences, to create a chatbot that is more selective in its learning, and thus resistant to becoming immoral the way Tay did

Think-aloud interviews: A tool for exploring student statistical reasoning

Research has shown that introductory statistics students hold many misconceptions, and that many of these are also present among practicing scientists. But statistics is becoming important to many new fields, and understanding how students learn statistics is more important than ever, if it is to be effectively taught. We describe an education research method intended to reveal how students think and to provide practical ways of measuring their understanding: a combination of think-aloud interviews and concept inventories. Think-aloud interviews give unprecedented insight into student thinking, while concept inventories can be administered to entire classes to measure learning. We demonstrate the method through insights gained from 42 think-aloud interviews with introductory students, plus large-scale concept inventory data from over 50 questions given as pre- and post-tests to hundreds of introductory statistics students at two institutions. Think-aloud interviews revealed previously under-reported misconceptions about sampling distributions and causation, while helping us refine conceptual questions to measure their prevalence at large scale. These insights, and the final questions, may help educators develop improved lessons, while suggesting directions for future statistics education research and providing practical tools for researchers to improve our understanding of student learning.Comment: 23 pages, 4 tables, 3 figures; supplemental data available online at https://doi.org/10.1184/R1/1005844

Fortifying or fragmenting the state? The political economy of the drug trade in Shan State, Myanmar, 1988-2012

Over the past twenty-five years, the government of Myanmar (Burma) has consolidated control over large parts of Shan State, neutralizing much of the threat posed by armed groups and strengthening its hold over revenue extraction. During this period Myanmar has retained its position as the world's second largest producer of illicit opium, much of which is converted into heroin within the country's borders. This article explores the relationship between state-building processes and the illicit opium/heroin economy in Shan State since 1988. The author has four aims. First, to reassess the theoretical assumptions that equate illicit economies with state fragility and demonstrate instead why illicit drug economies can become embedded in processes of conflict reduction and state consolidation. Second, to explain why establishing control over Shan State has become so important to the Myanmar government's state-building ambitions. Third, to analyze how the state's engagement with the drug trade has become a vital part of its attempts to consolidate control, in terms of financing military expansion and brokering deals with strongmen who are able to govern local populations. Finally, to assess how these strategies embody a form of “negotiated statehood” in which the state's growing control has been defined by attempts to manage, rather than monopolize, the means of coercion and extraction