Implementing Monte Carlo tests with P-value buckets

Software packages usually report the results of statistical tests using p-values. Users often interpret these by comparing them to standard thresholds, e.g. 0.1%, 1% and 5%, which is sometimes reinforced by a star rating (***, **, *). We consider an arbitrary statistical test whose p-value p is not available explicitly, but can be approximated by Monte Carlo samples, e.g. by bootstrap or permutation tests. The standard implementation of such tests usually draws a fixed number of samples to approximate p. However, the probability that the exact and the approximated p-value lie on different sides of a threshold (the resampling risk) can be high, particularly for p-values close to a threshold. We present a method to overcome this. We consider a finite set of user-specified intervals which cover [0,1] and which can be overlapping. We call these p-value buckets. We present algorithms that, with arbitrarily high probability, return a p-value bucket containing p. We prove that for both a bounded resampling risk and a finite runtime, overlapping buckets need to be employed, and that our methods both bound the resampling risk and guarantee a finite runtime for such overlapping buckets. To interpret decisions with overlapping buckets, we propose an extension of the star rating system. We demonstrate that our methods are suitable for use in standard software, including for low p-value thresholds occurring in multiple testing settings, and that they can be computationally more efficient than standard implementations

Herding Cats: Modelling, Simulation, Testing, and Data Mining for Weak Memory

We propose an axiomatic generic framework for modelling weak memory. We show how to instantiate this framework for SC, TSO, C++ restricted to release-acquire atomics, and Power. For Power, we compare our model to a preceding operational model in which we found a flaw. To do so, we define an operational model that we show equivalent to our axiomatic model. We also propose a model for ARM. Our testing on this architecture revealed a behaviour later acknowl-edged as a bug by ARM, and more recently 31 additional anomalies. We offer a new simulation tool, called herd, which allows the user to specify the model of his choice in a concise way. Given a specification of a model, the tool becomes a simulator for that model. The tool relies on an axiomatic description; this choice allows us to outperform all previous simulation tools. Additionally, we confirm that verification time is vastly improved, in the case of bounded model checking. Finally, we put our models in perspective, in the light of empirical data obtained by analysing the C and C++ code of a Debian Linux distribution. We present our new analysis tool, called mole, which explores a piece of code to find the weak memory idioms that it uses

Initiation of Breastfeeding and Factors Associated with Prelacteal Feeds in Central Nepal

Background: Prelacteal feeds and delayed initiation of breastfeeding may lead to undernutrition of the infant but are still prevalent in many countries.Objective: A prospective cohort community-based study was conducted in central Nepal to ascertain the rate of early breastfeeding initiation and factors associated with the introduction of prelacteal feeds.Methods: Breastfeeding information was collected from 639 women who recently gave birth in the Kaski district of central Nepal. Backward stepwise logistic regression analysis was performed to determine factors associated with the use of prelacteal feeds.Results: The incidence of prelacteal feeds was 9.1%, with infant formula being the most common prelacteal food. Approximately 67% and 90% of mothers breastfed within 1 hour and 4 hours of delivery, respectively. Women who reside in urban areas (odds ratio [OR] = 2.68; 95% confidence interval [CI], 1.35-5.39), first-time mothers (OR = 2.15; 95% CI,1.15-4.02), and those who underwent cesarean section (OR = 10.10; 95% CI, 5.47-18.67) were more likely to give prelacteal feeds to their infants.Conclusion: The early initiation of breastfeeding with colostrum as the first feed was common in the study area. The introduction of prelacteal feeds was associated with urban residency, first-time motherhood, and cesarean delivery

EC3: Elastic Cloud Computing Cluster

This paper introduces Elastic Cloud Computing Cluster (EC3), a tool that creates elastic virtual clusters on top of Infrastructure as a Service (IaaS) Clouds. The clusters are self-managed entities that scale out to a larger number of nodes on demand, up to a maximum size specified by the user. Whenever idle resources are detected, the clusters automatically scale in, according to some predefined policies, in order to cut down the costs in the case of using a public Cloud provider. This creates the illusion of a real cluster without requiring an investment beyond the actual usage. Two different case studies are presented to assess the effectiveness of an elastic virtual cluster. The results show that the usage of self-managed elastic clusters represents an important economic saving when compared both to physical clusters and to static virtual clusters deployed on an IaaS Cloud, with a reduced penalty in the elasticity management.©2013 Elsevier Inc. All rights reserved.The authors would like to thank the financial support received from the Generalitat Valenciana for the project GV/2012/076 and to the Ministerio de Ciencia e Innovacion for the project CodeCloud (TIN2010-17804).Caballer Fernández, M.; Alfonso Laguna, CD.; Alvarruiz Bermejo, F.; Moltó, G. (2013). EC3: Elastic Cloud Computing Cluster. Journal of Computer and System Sciences. 79(8):1341-1351. https://doi.org/10.1016/j.jcss.2013.06.005S1341135179

Is popular radio a source of exposure to alcohol references in mid to later life?:A content analysis

Background There is concern around alcohol consumption in mid to later life yet little understanding about what influences this behaviour. No previous research has explored the extent to which adults in mid to later life may be exposed to alcohol references in the media. This project aimed to determine the frequency of alcohol references on radio stations with a high proportion of listeners in mid to later life. Methods Content analysis of alcohol references on four popular UK music-based radio stations with a high proportion of listeners aged 55–64 years over three time points. Results Alcohol references occur frequently, but vary by time of year and type of radio station. When alcohol is mentioned its consumption is portrayed as the norm, without negative consequences. On three commercial stations, the majority of mentions came from advertising, whereas on BBC Radio 2 nearly all references were talk-based. All adverts for direct promotion of alcohol were by supermarkets. Alcohol was frequently associated with celebrations, socializing or something to consume for its own sake. Conclusions Adults in the age group 55–64 may be exposed to references to alcohol that could serve to reinforce norms of consumption of alcohol and promote purchases of cheap alcohol

Beyond mean modelling: Bias due to misspecification of dispersion in Poisson-inverse Gaussian regression.

In clinical trials one traditionally models the effect of treatment on the mean response. The underlying assumption is that treatment affects the response distribution through a mean location shift on a suitable scale, with other aspects of the distribution (shape/dispersion/variance) remaining the same. This work is motivated by a trial in Parkinson's disease patients in which one of the endpoints is the number of falls during a 10-week period. Inspection of the data reveals that the Poisson-inverse Gaussian (PiG) distribution is appropriate, and that the experimental treatment reduces not only the mean, but also the variability, substantially. The conventional analysis assumes a treatment effect on the mean, either adjusted or unadjusted for covariates, and a constant dispersion parameter. On our data, this analysis yields a non-significant treatment effect. However, if we model a treatment effect on both mean and dispersion parameters, both effects are highly significant. A simulation study shows that if a treatment effect exists on the dispersion and is ignored in the modelling, estimation of the treatment effect on the mean can be severely biased. We show further that if we use an orthogonal parametrization of the PiG distribution, estimates of the mean model are robust to misspecification of the dispersion model. We also discuss inferential aspects that are more difficult than anticipated in this setting. These findings have implications in the planning of statistical analyses for count data in clinical trials.The trial and post hoc analyses were funded by Lundbeck

Life-history trait variation in a queen-size dimorphic ant

1. Size polymorphism is often connected to alternative life-history traits, which may eventually lead to distinct size classes. In the ant Myrmica ruginodis, larger macrogyne and smaller microgyne queen morphs have been suggested to follow different reproductive strategies, which has presumably resulted in several differences in their key life-history traits. 2. In this study, we examine the association of queen-size morphs with colony queen number (monogyny vs. polygyny), dispersal and queen recruitment patterns, as well as habitat associations of the queen morphs. We do this by sampling established queens from a large number of excavated nests from several populations, estimating genetic relatedness among coexisting queens and pitfall trapping free-ranging wingless queens. 3. Our results show that associations of queen morphs with colony queen number and nest-founding strategy holds only partly. The morph frequencies vary widely across populations from practically pure macrogyne to more than 50% microgyne, but the expected association of macrogyne occurrence with monogyny and microgyne with polygyny is not universal. Dispersal and queen recruitment patterns also show that although most macrogynes participate in nuptial flights and most microgynes are recruited back to their natal nests, a fraction of both morphs use the alternative strategy. 4. The polygynous microgyne morph has been suggested to specialize in stable habitats, but our results from Finnish mesic heath forests do not support this. This study shows that factors other than just queen size also influence life-history trait variation and reproductive strategies in ants.Peer reviewe

Advancement of the German version of the moral distress scale for acute care nurses : a mixed methods study

Aim: Moral distress experienced by nurses in acute care hospitals can adversely impact the affected nurses, their patients and their hospitals; therefore, it is advisable for organizations to establish internal monitoring of moral distress. However, until now, no suitable questionnaire has been available for use in German‐speaking contexts. Hence, the aim of this study was to develop and psychometrically test a German‐language version of the Moral Distress Scale. Design: We chose a sequential explanatory mixed methods design, followed by a second quantitative cross‐sectional survey. Methods: An American moral distress scale was chosen, translated, culturally adapted, tested in a pilot study and subsequently used in 2011 to conduct an initial web‐based quantitative cross‐sectional survey of nurses in all inpatient units at five hospitals in Switzerland's German‐speaking region. Data were analysed descriptively and via a Rasch analysis. In 2012, four focus group interviews were conducted with 26 nurses and then evaluated using knowledge maps. The results were used to improve the questionnaire. In 2015, using the revised German‐language instrument, a second survey and Rasch analysis were conducted. Results: The descriptive results of the first survey's participants (n = 2153; response rate: 44%) indicated that moral distress is a salient phenomenon in Switzerland. The data from the focus group interviews and the Rasch analysis produced information valuable for the questionnaire's further development. Alongside the data from the second survey's participants (n = 1965; response rate: 40%), the Rasch analysis confirmed the elimination of previous deficiencies on its psychometrics. A Rasch‐scaled German version of the Moral Distress Scale is now available for use

Determinants of facility delivery after implementation of safer mother programme in Nepal: A prospective cohort study

Background: There are several barriers for pregnant women to deliver in a health care facility. This prospective cohort study investigated factors affecting facility delivery and reasons for unplanned place of delivery after implementation of the safer mother programme in Nepal. Methods: Baseline interviews using a validated questionnaire were conducted on a sample of 700 pregnant women representative of the Kaski district in central Nepal. Follow-up interviews of the cohort were then conducted within 45 days postpartum. Stepwise logistic regression analysis was performed to determine factors associated with the facility delivery outcome. Results: Of the 644 pregnant women whose delivery location had been identified, 547 (85%) gave birth in a health care facility. Women were more likely to deliver in a health facility if they were educated especially with higher secondary or above qualification (adjusted odds ratio (OR) 12.39, 95% confidence interval (CI) 5.09 to 30.17), attended 4 or more antenatal care visits (OR 2.15, 95% CI 1.25 to 3.69), and lived within 30 minutes to the facility (OR 11.61, 95% CI 5.77 to 24.04). For the 97 women who delivered at home, 72 (74.2%) were unplanned, mainly due to quick precipitation of labour making it impossible to reach a health facility. Conclusions: It appeared that facility delivery occurs more frequent among educated women and those who live nearby, even though maternity services are now freely available in Nepal. Because of the difficult terrain and transportation problem in rural areas, interventions that make maternity service physically accessible during antenatal period are needed to increase the utilisation of health facility for child birth