Searching and Stopping: An Analysis of Stopping Rules and Strategies

Searching naturally involves stopping points, both at a query level (how far down the ranked list should I go?) and at a session level (how many queries should I issue?). Understanding when searchers stop has been of much interest to the community because it is fundamental to how we evaluate search behaviour and performance. Research has shown that searchers find it difficult to formalise stopping criteria, and typically resort to their intuition of what is "good enough". While various heuristics and stopping criteria have been proposed, little work has investigated how well they perform, and whether searchers actually conform to any of these rules. In this paper, we undertake the first large scale study of stopping rules, investigating how they influence overall session performance, and which rules best match actual stopping behaviour. Our work is focused on stopping at the query level in the context of ad-hoc topic retrieval, where searchers undertake search tasks within a fixed time period. We show that stopping strategies based upon the disgust or frustration point rules - both of which capture a searcher's tolerance to non-relevance - typically result in (i) the best overall performance, and (ii) provide the closest approximation to actual searcher behaviour, although a fixed depth approach also performs remarkably well. Findings from this study have implications regarding how we build measures, and how we conduct simulations of search behaviours

Optimal Supersaturated Designs for Lasso Sign Recovery

Supersaturated designs, in which the number of factors exceeds the number of runs, are often constructed under a heuristic criterion that measures a design's proximity to an unattainable orthogonal design. Such a criterion does not directly measure a design's quality in terms of screening. To address this disconnect, we develop optimality criteria to maximize the lasso's sign recovery probability. The criteria have varying amounts of prior knowledge about the model's parameters. We show that an orthogonal design is an ideal structure when the signs of the active factors are unknown. When the signs are assumed known, we show that a design whose columns exhibit small, positive correlations are ideal. Such designs are sought after by the Var(s+)-criterion. These conclusions are based on a continuous optimization framework, which rigorously justifies the use of established heuristic criteria. From this justification, we propose a computationally-efficient design search algorithm that filters through optimal designs under different heuristic criteria to select the one that maximizes the sign recovery probability under the lasso

Tetra­pyrazine­platinum(II) bis­(tetra­fluoro­borate) acetonitrile hemisolvate

The improved synthesis and characterization of tetra­pyrazine­platinum(II) bis­(tetra­fluoro­borate) acetonitrile hemisolvate, [Pt(C4H4N2)4](BF4)2·0.5CH3CN, is reported. The unit cell contains a half equivalent of an acetonitrile solvent mol­ecule per tetra­pyrazine­platinum(II) ion. The coordination geometry of the PtII ion is almost square-planar, with the Pt atom residing on an inversion center. The BF4 − counter-anion, located at a general position, has an idealized tetra­hedral geometry and an acetonitrile solvent mol­ecule, the methyl group of which is disordered over two equal positions, sits on a twofold rotation axis

Chlorido(4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine)­platinum(II) chloride toluene monosolvate

In the title compound, [PtCl(C27H35N3)]Cl·C7H8, the PtII atom is coordinated in a pseudo-square-planar fashion by the N atoms of a 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine (tbtrpy) ligand and a Cl atom. The Pt—N distance of the N atom on the central pyridine is 1.941 (4) Å, while the peripheral N atoms have Pt—N distances of 2.015 (4) and 2.013 (4) Å. The Pt—Cl bond distance is 2.3070 (10) Å. The cations pack as dimers in a head-to-tail orientation with an inter­molecular Pt⋯Pt distance of 3.2774 (3) Å and Pt⋯N distances of 3.599 (4), 3.791 (4) and 4.115 (4) Å. The solvent mol­ecule is disordered and occupies two positions with a ratio of 0.553 (6):0.447 (6)

Chlorido(4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine)­platinum(II) tetra­fluorido­borate

In the title compound, [PtCl(C27H35N3)]BF4, the PtII atom is in a pseudo-square-planar coordination, which is typical of Pt–terpyridine complexes. The Pt—Cl bond distance is 2.2998 (7) Å. The Pt—N distance of the N atom on the central pyridine is 1.931 (2) Å, while the peripheral N atoms have Pt—N distances of 2.018 (2) and 2.022 (2) Å. The cations pack as dimers in a head-to-tail orientation with an inter­molecular Pt⋯Pt distance of 3.5214 (2) Å and Pt⋯N distances of 3.527 (2), 3.873 (2) and 4.532 (2) Å. In the crystal, cations and anions are linked by weak C—H⋯F hydrogen-bonding inter­actions

PubMed related articles: a probabilistic topic-based model for content similarity

<p>Abstract</p> <p>Background</p> <p>We present a probabilistic topic-based model for content similarity called <it>pmra </it>that underlies the related article search feature in PubMed. Whether or not a document is about a particular topic is computed from term frequencies, modeled as Poisson distributions. Unlike previous probabilistic retrieval models, we do not attempt to estimate relevance–but rather our focus is "relatedness", the probability that a user would want to examine a particular document given known interest in another. We also describe a novel technique for estimating parameters that does not require human relevance judgments; instead, the process is based on the existence of MeSH ^®in MEDLINE ^®.</p> <p>Results</p> <p>The <it>pmra </it>retrieval model was compared against <it>bm25</it>, a competitive probabilistic model that shares theoretical similarities. Experiments using the test collection from the TREC 2005 genomics track shows a small but statistically significant improvement of <it>pmra </it>over <it>bm25 </it>in terms of precision.</p> <p>Conclusion</p> <p>Our experiments suggest that the <it>pmra </it>model provides an effective ranking algorithm for related article search.</p

Children’s Feedback Preferences in Response to an Experimentally Manipulated Peer Evaluation Outcome: The Role of Depressive Symptoms

The present study examined the linkage between pre-adolescent children’s depressive symptoms and their preferences for receiving positive vs. negative feedback subsequent to being faced with an experimentally manipulated peer evaluation outcome in real time. Participants (n = 142) ages 10 to 13, played a computer contest based on the television show Survivor and were randomized to either a peer rejection (i.e., receiving the lowest total ‘likeability’ score from a group of peer-judges), a peer success (i.e., receiving the highest score), or a control peer evaluation condition. Children’s self-reported feedback preferences were then assessed. Results revealed that participants assigned to the negative evaluation outcome, relative to either the success or the control outcome, showed a significantly higher subsequent preference for negatively tuned feedback. Contrary to previous work and predictions derived from self-verification theory, children higher in depressive symptoms were only more likely to prefer negative feedback in response to the negative peer evaluation outcome. These effects for depression were not accounted for by either state mood at baseline or mood change in response to the feedback manipulation

Communicating Auditory Impairments Using Electroacoustic Composition

Changes in human sensory perception can occur for a variety of reasons. In the case of distortions or transformations in the human auditory system, the aetiology may include factors such as medical conditions affecting cognition or physiology, interaction of the ears with mechanical waves, or stem from chemically induced sources, such the consumption of alcohol. These changes may be permanent, intermittent, or temporary. In order to communicate such effects to an audience in an accessible, and easily understood manner, a series of electroacoustic compositions were produced. This concept follows on from previous work on the theme of representing auditory hallucinations. Specifically, these compositions relate to auditory impairments that humans can experience due to tinnitus or through the consumption of alcohol. In the case of tinnitus, whilst much is known about the causes and symptoms, the experience of what it is like to live with tinnitus is less explored and those who have acquired the condition may often feel frustration when trying to convey the experience of ‘what it is like’ for them. In terms of impairment from alcohol consumption, whilst there is much hearsay, little research exists on the immediate and short-term effects of alcohol consumption on the human auditory system, despite over half of the UK population reported as consuming alcohol in 2017. The methodology employed to design these compositions draws upon scientific research findings, including experimental and explorative studies involving human participants, coupled with electroacoustic composition techniques. The pieces are typically constructed by mixing field recordings with synthesised materials and incorporating a range of temporal and frequency domain manipulations to the elements therein. In this way, the listener is able to experience the phenomenon in a recognisable context, where distortions of reality can be emulated to varying degrees. It is intended that these compositions can serve as easily accessible and understood examples of auditory impairments and that they might find utility in the communication of symptoms to those who have never experienced the underlying causes or conditions. This presents opportunities for pieces like these to be used in scenarios such as education and public health awareness campaigns