Skellam process with resetting: a neural spike train model.

This paper introduces the Skellam process with resetting. Resetting is a modification that accommodates the modeling of neural spike trains. We show this as a biologically plausible model, which codes the information content of neural spike trains with three, potentially, time-varying functions. We show that the interspike interval distribution under this model follows a mixture of gamma distributions, a flexible class covering a wide range of commonly used models. Through simulation studies and the analyses of connected retinal ganglion and lateral geniculate nucleus cells, we evaluate the performance of this model. Copyright © 2016 John Wiley & Sons, Ltd.

Surfing Behind a Boat: Quality and Reliability of Online Resources on Scaphoid Fractures.

BACKGROUND: Patients seeking information and advice on treatment of scaphoid fractures unknowingly confront longstanding medical controversies surrounding the management of this condition. However, there are no studies specifically looking into the quality and reliability of online information on scaphoid fractures. METHODS: We identified 44 unique websites for evaluation using the term "scaphoid fractures". The websites were categorized by type and assessed using the DISCERN score, the Journal of the American Medical Association (JAMA) benchmark criteria and the Health on the net (HON) code. RESULTS: The majority of websites were commercial (n = 13) followed by academic (n = 12). Only seven of the websites were HON certified. The mean DISCERN score was 43.8. Only 4 websites scored 63 or above representing excellent quality with minimal shortcomings but 13 websites scored 38 or below representing poor or very poor quality. The mean JAMA benchmark criteria score was 2.2. The Governmental and Non-Profit Organizations category websites had the highest mean JAMA benchmark score. The websites that displayed the HON-code seal had higher mean DISCERN scores and higher mean JAMA benchmark scores compared to websites that did not display the seal. CONCLUSIONS: Good quality health information is certainly available on the Internet. However, it is not possible to predict with certainty which sites are of higher quality. We suggest clinicians should have a responsibility to educate their patients regarding the unregulated nature of medical information on the internet and proactively provide patients with educational resources and thus help them make smart and informed decisions.

Individualized predictions of time to menopause using multiple measurements of antimüllerian hormone.

OBJECTIVE: The ability of antimüllerian hormone (AMH) to predict age at menopause has been reported in several studies, and a decrease in AMH level has been found to increase the probability of menopause. The rate of decline varies among women, and there is also a variability of decline between women's cycles. As a result, individualized evaluation is required to accurately predict time of menopause. To this end, we have used the AMH trajectories of individual women to predict each one's age at menopause. METHODS: From a cohort study, 266 women (ages 20-50 y) who had regular and predictable menstrual cycles at the initiation of the study were randomly selected from among 1,265 women for multiple AMH measurements. Participants were visited at approximately 3-year intervals and followed for an average of 6.5 years. Individual likelihood of menopause was predicted by fitting the shared random-effects joint model to the baseline covariates and the specific AMH trajectory of each woman. RESULTS: In total, 23.7% of the women reached menopause during the follow-up period. The estimated mean (SD) AMH concentration at the time of menopause was 0.05 ng/mL (0.06 ng/mL), compared with 1.36 ng/mL (1.85 ng/mL) for those with a regular menstrual cycle at their last assessment. The decline rate in the AMH level varied among age groups, and age was a significant prognostic factor for AMH level (P < 0.001). Adjusting for age and body mass index, each woman had her own specific AMH trajectory. Lower AMH and older age had significant effects on the onset of menopause. Individualized prediction of time to menopause was obtained from the fitted model. CONCLUSIONS: Longitudinal measurements of AMH will enable physicians to individualize the prediction of menopause, thereby facilitating counseling on the timing of childbearing or medical management of health issues associated with menopause.

Estimating the mean and standard deviation of environmental data with below detection limit observations: Considering highly skewed data and model misspecification.

In environmental studies, concentration measurements frequently fall below detection limits of measuring instruments, resulting in left-censored data. Some studies employ parametric methods such as the maximum likelihood estimator (MLE), robust regression on order statistic (rROS), and gamma regression on order statistic (GROS), while others suggest a non-parametric approach, the Kaplan-Meier method (KM). Using examples of real data from a soil characterization study in Montreal, we highlight the need for additional investigations that aim at unifying the existing literature. A number of studies have examined this issue; however, those considering data skewness and model misspecification are rare. These aspects are investigated in this paper through simulations. Among other findings, results show that for low skewed data, the performance of different statistical methods is comparable, regardless of the censoring percentage and sample size. For highly skewed data, the performance of the MLE method under lognormal and Weibull distributions is questionable; particularly, when the sample size is small or censoring percentage is high. In such conditions, MLE under gamma distribution, rROS, GROS, and KM are less sensitive to skewness. Related to model misspecification, MLE based on lognormal and Weibull distributions provides poor estimates when the true distribution of data is misspecified. However, the methods of rROS, GROS, and MLE under gamma distribution are generally robust to model misspecifications regardless of skewness, sample size, and censoring percentage. Since the characteristics of environmental data (e.g., type of distribution and skewness) are unknown a priori, we suggest using MLE based on gamma distribution, rROS and GROS.

Perthes Disease: The Quality and Reliability of Information on the Internet.

BACKGROUND: Research has shown that up to 89% of parents used the Internet to seek health information regarding their child's medical condition. Much of the information on the Internet is valuable; however, the quality of health information is variable and unregulated. The aim of this study was to evaluate the quality and content of information about Perthes disease on the Internet using recognized scoring systems, identification of quality markers, and describe a novel specific score. METHODS: We searched the top 3 search engines (Google, Yahoo!, and Bing) for the following keywords: "Perthes disease." Forty-five unique Web sites were identified. The Web sites were then categorized by type and assessed using the DISCERN score, the Journal of the American Medical Association (JAMA) benchmark criteria, and a novel Perthes-specific Content score. The presence of the Health On the Net (HON) code, a reported quality assurance marker, was noted. RESULTS: Of the Web sites analyzed, the Majority were Governmental and Nonprofit Organizations (NPO) (37.8%), followed by commercial Web sites (22.2%). Only 6 of the Web sites were HONcode certified. The mean DISCERN score was 53.1 (SD=9.0). The Governmental and NPO Web sites had the highest overall DISCERN scores followed closely by Physician Web sites. The mean JAMA benchmark criteria score was 2.1 (SD=1.2). Nine Web sites had maximal scores and the Academic Web sites had the highest overall JAMA benchmark scores. DISCERN scores, JAMA benchmark scores, and Perthes-specific Content scores were all greater for Web sites that bore the HONcode seal. CONCLUSIONS: The quality of information available online regarding Perthes disease is of variable quality. Governmental and NPO Web sites predominate and also provide higher quality content. The HONcode seal is a reliable indicator of Web site quality. CLINICAL RELEVANCE: Physicians should recommend the HONcode seal to their patients as a reliable indicator of Web site quality or, better yet, refer patients to sites they have personally reviewed. Supplying parents with a guide to health information on the Internet will help exclude Web sites as sources of misinformation.

Surfing for hip replacements: has the "internet tidal wave" led to better quality information.

This study aimed to determine the quality of information available on the internet regarding Total Hip Replacement (THR). The unique websites identified were categorised by type and assessed using the DISCERN score, the Journal of the American Medical Association (JAMA) benchmark criteria, and a novel (THR)-specific content score. The presence of the Health On the Net (HON) code, a reported quality assurance marker, was noted. Commercial websites predominate. Governmental & Non-Profit Organizations websites attained the highest DISCERN score. Sites that bore the HONcode seal obtained significantly higher DISCERN and THR content scores than those without the certification. Physicians should recommend the HONcode seal to their patients as a reliable indicator of website quality or, better yet, refer patients to sites they have personally reviewed.

Multiscale analysis of neural spike trains.

This paper studies the multiscale analysis of neural spike trains, through both graphical and Poisson process approaches. We introduce the interspike interval plot, which simultaneously visualizes characteristics of neural spiking activity at different time scales. Using an inhomogeneous Poisson process framework, we discuss multiscale estimates of the intensity functions of spike trains. We also introduce the windowing effect for two multiscale methods. Using quasi-likelihood, we develop bootstrap confidence intervals for the multiscale intensity function. We provide a cross-validation scheme, to choose the tuning parameters, and study its unbiasedness. Studying the relationship between the spike rate and the stimulus signal, we observe that adjusting for the first spike latency is important in cross-validation. We show, through examples, that the correlation between spike trains and spike count variability can be multiscale phenomena. Furthermore, we address the modeling of the periodicity of the spike trains caused by a stimulus signal or by brain rhythms. Within the multiscale framework, we introduce intensity functions for spike trains with multiplicative and additive periodic components. Analyzing a dataset from the retinogeniculate synapse, we compare the fit of these models with the Bayesian adaptive regression splines method and discuss the limitations of the methodology. Computational efficiency, which is usually a challenge in the analysis of spike trains, is one of the highlights of these new models. In an example, we show that the reconstruction quality of a complex intensity function demonstrates the ability of the multiscale methodology to crack the neural code.

Reducing the threat of in-transit derailments involving dangerous goods through effective placement along the train consist.

Train derailments are important safety concerns, and they become increasingly so when dangerous goods (DG) are involved. One way to reduce the risk of DG derailments is through effective DG railway car placement along the train consist. This paper investigates the relationship between DG railway car placement and derailment for different route attributes and DG shipments. A model is presented for estimating the probability of derailment by position, based on the estimated point of derailment (POD) and the number of cars derailing. A DG placement model that considers in-transit derailment risk is shown to provide a sound scientific basis for effective DG marshalling in conventional rail hump yard operations.

Comparison of two populations of curves with an application in neuronal data analysis.

Often in neurophysiological studies, scientists are interested in testing hypotheses regarding the equality of the overall intensity functions of a group of neurons when recorded under two different experimental conditions. In this paper, we consider such a hypothesis testing problem. We propose two test statistics: a parametric test similar to the modified Hotelling's T2 statistic of Behseta and Kass (Statist. Med. 2005; 24:3523­3534), as well as a nonparametric one similar to the spatial signed-rank test statistic of Möttönen and Oja (J. Nonparametric Statist. 1995; 5:201­213). We implement these tests on smooth curves obtained via fitting Bayesian Adaptive Regression Splines (BARS) to the intensity functions of neuronal Peri-Stimulus Time Histograms. Through simulation, we show that the powers of our proposed tests are extremely high even when the number of sampled neurons and the number of trials per neuron are small. Finally, we apply our methods on a group of motor cortex neurons recorded during a reaching task.

Turning behavior in healthy older adults: Is there a preference for step versus spin turns?

This research examined the prevalence of step turns and spin turns during turning while walking in healthy older adults. The potential effect of magnitude of the turn and walking velocity on the prevalence of the step and spin turns were also investigated by examining the participants' performance as they made 45 degrees and 90 degrees turns while walking at three different velocities. Results showed that healthy older adults in our study preferred spin turns while walking either slower or faster than their natural walking speed. Only during 90 degrees turns while walking fast the participants showed a preference for step turns over spin turns. Spin turns are less stable and have a greater biomechanical cost than step turns. The high incidence of spin turns in older adults may contribute to the higher risk of falling in this population.