Retrospective model-based inference guides model-free credit assignment

An extensive reinforcement learning literature shows that organisms assign credit efficiently, even under conditions of state uncertainty. However, little is known about credit-assignment when state uncertainty is subsequently resolved. Here, we address this problem within the framework of an interaction between model-free (MF) and model-based (MB) control systems. We present and support experimentally a theory of MB retrospective-inference. Within this framework, a MB system resolves uncertainty that prevailed when actions were taken thus guiding an MF credit-assignment. Using a task in which there was initial uncertainty about the lotteries that were chosen, we found that when participants’ momentary uncertainty about which lottery had generated an outcome was resolved by provision of subsequent information, participants preferentially assigned credit within a MF system to the lottery they retrospectively inferred was responsible for this outcome. These findings extend our knowledge about the range of MB functions and the scope of system interactions

A paediatric bone index derived by automated radiogrammetry

Hand radiographs are obtained routinely to determine bone age of children. This paper presents a method that determines a Paediatric Bone Index automatically from such radiographs. The Paediatric Bone Index is designed to have minimal relative standard deviation (7.5%), and the precision is determined to be 1.42%. Introduction We present a computerised method to determine bone mass of children based on hand radiographs, including a reference database for normal Caucasian children. Methods Normal Danish subjects (1,867), of ages 7-17, and 531 normal Dutch subjects of ages 5-19 were included. Historically, three different indices of bone mass have been used in radiogrammetry all based on A = pi TW(1 - T/W), where T is the cortical thickness and W the bone width. The indices are the metacarpal index A/W-2, DXR-BMD=A/W, and Exton-Smith's index A/(WL), where L is the length of the bone. These indices are compared with new indices of the form A/((WLb)-L-a), and it is argued that the preferred index has minimal SD relative to the mean value at each bone age and sex. Finally, longitudinal series of X-rays of 20 Japanese children are used to derive the precision of the measurements. Results The preferred index is A/((WL0.33)-L-1.33), which is named the Paediatric Bone Index, PBI. It has mean relative SD 7.5% and precision 1.42%. Conclusions As part of the BoneXpert method for automated bone age determination, our method facilitates retrospective research studies involving validation of the proposed index against fracture incidence and adult bone mineral densit

Estimating the number needed to treat from continuous outcomes in randomised controlled trials: methodological challenges and worked example using data from the UK Back Pain Exercise and Manipulation (BEAM) trial

Background Reporting numbers needed to treat (NNT) improves interpretability of trial results. It is unusual that continuous outcomes are converted to numbers of individual responders to treatment (i.e., those who reach a particular threshold of change); and deteriorations prevented are only rarely considered. We consider how numbers needed to treat can be derived from continuous outcomes; illustrated with a worked example showing the methods and challenges. Methods We used data from the UK BEAM trial (n = 1, 334) of physical treatments for back pain; originally reported as showing, at best, small to moderate benefits. Participants were randomised to receive 'best care' in general practice, the comparator treatment, or one of three manual and/or exercise treatments: 'best care' plus manipulation, exercise, or manipulation followed by exercise. We used established consensus thresholds for improvement in Roland-Morris disability questionnaire scores at three and twelve months to derive NNTs for improvements and for benefits (improvements gained+deteriorations prevented). Results At three months, NNT estimates ranged from 5.1 (95% CI 3.4 to 10.7) to 9.0 (5.0 to 45.5) for exercise, 5.0 (3.4 to 9.8) to 5.4 (3.8 to 9.9) for manipulation, and 3.3 (2.5 to 4.9) to 4.8 (3.5 to 7.8) for manipulation followed by exercise. Corresponding between-group mean differences in the Roland-Morris disability questionnaire were 1.6 (0.8 to 2.3), 1.4 (0.6 to 2.1), and 1.9 (1.2 to 2.6) points. Conclusion In contrast to small mean differences originally reported, NNTs were small and could be attractive to clinicians, patients, and purchasers. NNTs can aid the interpretation of results of trials using continuous outcomes. Where possible, these should be reported alongside mean differences. Challenges remain in calculating NNTs for some continuous outcomes

Rationalizing Critical Cost Overrun Factors on Public Sector Housing Programmes

The cost overrun phenomenon on projects worldwide creates a major source of risk that warrants investigation. The prevailing factor school of thought provides strong empirical evidence that critical factors contributing to cost overruns are both context-specific and project-specific. Although many studies have been conducted identifying factors and causes of cost overruns, very few studies have investigated root causes. Additionally, a limited body of knowledge is available within the context of Small Island Development States (SIDS). To fill this gap, the objectives of this study were to identify and determine the main critical factors contributing to the cost overrun phenomenon in public sector social housing programmes (PSSHPs). These selected factors were thereafter categorized under leading root causes, and their severity was determined based on primary stakeholders’ perspectives. One hundred and twenty-three factors were identified from the literature, of which forty-one critical factors were extracted and grouped under four root causes based on a pilot survey of relevant public sector housing experts in the Trinidadian and Jamaican construction sectors. These refined factors and root causes were formulated into a questionnaire survey. One hundred and five responses were obtained from professionals who had a minimum of five years’ experience in various phases of public housing delivery. The severity of these critical factors was evaluated, ranked, and categorized using the relative importance index (RII) approach. The findings uncovered the leading root cause, which is political in nature. The top five critical factors are the selection of politically aligned contractors, the intentional design of inadequate contracts, the project actors' deliberately underestimating costs, the partisan project management team, and strategic misrepresentation. These findings are unique to SIDS and contribute to knowledge to reframe contemporary project management practices, which focus mainly on technical causes. Finally, as existing technical solutions are ineffective in curbing cost overruns in PSSHPs, these findings also inform public sector policymakers to focus on prioritization, control, and mitigation of political risks in formulating effective governance mechanisms

Implications of 'Lock-in' on Public Sector Project Management in a Small Island Development State

The concept of ‘Lock-In’, or the escalating cost of overcommitment on a project to a failing course of action, has unforeseeable implications in project management. This paper presents a case study on the occurrence and consequences of lock-in within the context of public sector housing projects in a small island developing state (SIDS). It demonstrates that cost overruns continue beyond the commissioning phase and throughout the project’s lifecycle, even though technical contingencies were implemented to deliver the intended project benefits. The findings unpack the implications of political expediency as a strategic tool mobilised to supersede proper technical decision-making prior to project execution. It concludes that project practitioners’ commitment to select and continue with a sub-optimal project can lead to the implementation of ineffective solutions to justify their actions, resulting in failed outcomes with negative social consequences. This research helps to advance project management knowledge in the us-er/operation phase, because previous scholarly work was limited to investigating lock-in from project conceptualisation to the commissioning phase

Shock waves in strongly coupled plasmas

Shock waves are supersonic disturbances propagating in a fluid and giving rise to dissipation and drag. Weak shocks, i.e., those of small amplitude, can be well described within the hydrodynamic approximation. On the other hand, strong shocks are discontinuous within hydrodynamics and therefore probe the microscopics of the theory. In this paper we consider the case of the strongly coupled N=4 plasma whose microscopic description, applicable for scales smaller than the inverse temperature, is given in terms of gravity in an asymptotically $AdS_5$ space. In the gravity approximation, weak and strong shocks should be described by smooth metrics with no discontinuities. For weak shocks we find the dual metric in a derivative expansion and for strong shocks we use linearized gravity to find the exponential tail that determines the width of the shock. In particular we find that, when the velocity of the fluid relative to the shock approaches the speed of light $v\to 1$ the penetration depth $\ell$ scales as $\ell\sim (1-v^2)^{1/4}$. We compare the results with second order hydrodynamics and the Israel-Stewart approximation. Although they all agree in the hydrodynamic regime of weak shocks, we show that there is not even qualitative agreement for strong shocks. For the gravity side, the existence of shock waves implies that there are disturbances of constant shape propagating on the horizon of the dual black holes.Comment: 47 pages, 8 figures; v2:typos corrected, references adde

A Spatial Analysis of Rift Valley Fever Virus Seropositivity in Domestic Ruminants in Tanzania

Rift Valley fever (RVF) is an acute arthropod-borne viral zoonotic disease primarily occurring in Africa. Since RVF-like disease was reported in Tanzania in 1930, outbreaks of the disease have been reported mainly from the eastern ecosystem of the Great Rift Valley. This cross-sectional study was carried out to describe the variation in RVF virus (RVFV) seropositivity in domestic ruminants between selected villages in the eastern and western Rift Valley ecosystems in Tanzania, and identify potential risk factors. Three study villages were purposively selected from each of the two Rift Valley ecosystems. Serum samples from randomly selected domestic ruminants (n = 1,435) were tested for the presence of specific immunoglobulin G (IgG) and M (IgM), using RVF enzyme-linked immunosorbent assay methods. Mixed effects logistic regression modelling was used to investigate the association between potential risk factors and RVFV seropositivity. The overall RVFV seroprevalence (n = 1,435) in domestic ruminants was 25.8% and species specific seroprevalence was 29.7%, 27.7% and 22.0% in sheep (n = 148), cattle (n = 756) and goats (n = 531), respectively. The odds of seropositivity were significantly higher in animals sampled from the villages in the eastern than those in the western Rift Valley ecosystem (OR = 1.88, CI: 1.41, 2.51; p<0.001), in animals sampled from villages with soils of good than those with soils of poor water holding capacity (OR = 1.97; 95% CI: 1.58, 3.02; p< 0.001), and in animals which had been introduced than in animals born within the herd (OR = 5.08, CI: 2.74, 9.44; p< 0.001). Compared with animals aged 1-2 years, those aged 3 and 4-5 years had 3.40 (CI: 2.49, 4.64; p< 0.001) and 3.31 (CI: 2.27, 4.82, p< 0.001) times the odds of seropositivity. The findings confirm exposure to RVFV in all the study villages, but with a higher prevalence in the study villages from the eastern Rift Valley ecosystem

How to find an attractive solution to the liar paradox

The general thesis of this paper is that metasemantic theories can play a central role in determining the correct solution to the liar paradox. I argue for the thesis by providing a specific example. I show how Lewis’s reference-magnetic metasemantic theory may decide between two of the most influential solutions to the liar paradox: Kripke’s minimal fixed point theory of truth and Gupta and Belnap’s revision theory of truth. In particular, I suggest that Lewis’s metasemantic theory favours Kripke’s solution to the paradox over Gupta and Belnap’s. I then sketch how other standard criteria for assessing solutions to the liar paradox, such as whether a solution faces a so-called revenge paradox, fit into this picture. While the discussion of the specific example is itself important, the underlying lesson is that we have an unused strategy for resolving one of the hardest problems in philosophy

When Parallel Schools of Thought Fail to Converge: The Case of Cost Overruns in Project Management

This paper investigates the conflicting and contrasting views between two prominent schools of thought (SOT), the conventional project management empirical school and the incoming behavioural and psychological sciences, to explain the cost overrun phenomenon in transportation infrastructure projects. Although theories within these SOTs seem to coexist and are used interchangeably, there exists a widening knowledge gap that leads to conflicting and contrasting ideological views. In this paper, we contend that there is a lack of a cross-fertilisation mechanism to fuse and co-join contemporary theories on cost overruns. This has led to the encapsulation and fragmented adhocracy in theory building. Utilising a critical review approach, this study proposes the concepts of ideological distancing and encapsulation between “empiricism” and “behavioural” SOTs as the focus of analyses for understanding the root causes of cost overruns in project studies. The study showed that the extant debate on cost overruns is limited and divergent, effectively contributing to the problem of continued expansion and non-convergence of theories that maintain parallel identities. This creates a space for inquiry, reflecting, theorising, and debating for the convergence of SOTs on cost overrun research and theories on what can be deemed project knowledge. This paper contributes to extant project studies by identifying the need for convergence and co-joining theories with different epistemes through causal linkages. Consequently, this will improve the public sector’s infrastructure policymaking by exposing the theoretical limitations of the current ad hoc manner and application of project management concepts based on the project professionals’ bounded decision-making rationalities

The rapid growth of a pleomorphic adenoma of the parotid gland in the third trimester of pregnancy

<p>Abstract</p> <p>Introduction</p> <p>We report a case highlighting the multidisciplinary management of a giant pleomorphic adenoma of the parotid gland that showed rapid growth in the third trimester of pregnancy.</p> <p>Case presentation</p> <p>A 43-year-old Caucasian woman presented in her 32nd week of gestation with a tumor of the parotid gland. Ultrasonography of her neck showed a parotid lesion of 40 × 30 × 27.5 mm. A follow-up magnetic resonance imaging scan of the neck four weeks later revealed that the tumor had grown to 70 × 60 × 60 mm, reaching the parapharyngeal space with marked obstruction of the oropharynx of about 50%. After discussing the case with our multidisciplinary tumor board and the gynecologists it was decided to deliver the baby by caesarean section in the 38th week of gestation, and then to perform a surgical resection of the tumor.</p> <p>Conclusion</p> <p>Indications for early surgical intervention of similar cases should be discussed on an individual patient basis in a multidisciplinary setting.</p