A dynamic trajectory class model for intensive longitudinal categorical outcome

This paper presents a novel dynamic latent class model for a longitudinal response that is frequently measured as in our prospective study of older adults with monthly data on activities of daily living for more than 10 years. The proposed method is especially useful when the longitudinal response is measured much more frequently than other relevant covariates. The trajectory classes are latent classes that represent distinct temporal patterns of the longitudinal response wherein an individual may remain in a trajectory class or switch to another as the class membership predictors are updated periodically over time. The identification of a common set of trajectory classes allows changes among the temporal patterns to be distinguished from local fluctuations in the response. Within a trajectory class, the longitudinal response is modeled by a class‐specific generalized linear mixed model. An informative event such as death is jointly modeled by class‐specific probability of the event through shared random effects with that for the longitudinal response. We do not impose the conditional independence assumption given the classes. We illustrate the method by analyzing the change over time in activities of daily living trajectory class among 754 older adults with 70,500 person‐months of follow‐up in the Precipitating Events Project. We also investigate the impact of jointly modeling the class‐specific probability of the event on the parameter estimates in a simulation study. The primary contribution of our paper is the periodic updating of trajectory classes for a longitudinal categorical response without assuming conditional independence. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of Stretchable,Environmentally Stable,Conducting Polymer PEDOT Using a Modified Acid Template Random Copolymer

Although poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has good electrical conductivity and high transparency in most applications, its usage in stretchable applications is limited because of its rigidity, reduced conductivity after elongation, and poor environmental stability. This study addresses these issues by incorporating the soft and relatively hydrophobic moiety poly(ethylene glycol) methacrylate (PEGMA). By incorporating PEGMA randomly in the rigid PSS chain, a soft and hydrophobic copolymer P(SS‐co‐PEGMA) is obtained. The conducting P(SS‐co‐PEGMA)‐based polymer‐coated PET film exhibits good resistance even after 400% elongation. In addition, PEDOT:P(SS‐co‐PEGMA) has better environmental stability than PEDOT:PSS because of the presence of the relatively hydrophobic PEGMA moiety in the chain. Moreover, the potential applicability of the synthesized flexible and stretchable electronic material as a stretchable matrix is established, which includes inorganic conductors (AgNW). When this material is stretched, it can be applied as a conductive interconnector to maintain the electrical pathway, instead of the other insulating matrices.     

Does Self-Selection Affect Samples’ Representativeness in Online Surveys? An Investigation in Online Video Game Research

Background

The number of medical studies performed through online surveys has increased dramatically in recent years. Despite their numerous advantages (eg, sample size, facilitated access to individuals presenting stigmatizing issues), selection bias may exist in online surveys. However, evidence on the representativeness of self-selected samples in online studies is patchy.

Objective

Our objective was to explore the representativeness of a self-selected sample of online gamers using online players’ virtual characters (avatars).

Methods

All avatars belonged to individuals playing World of Warcraft (WoW), currently the most widely used online game. Avatars’ characteristics were defined using various games’ scores, reported on the WoW’s official website, and two self-selected samples from previous studies were compared with a randomly selected sample of avatars.

Results

We used scores linked to 1240 avatars (762 from the self-selected samples and 478 from the random sample). The two self-selected samples of avatars had higher scores on most of the assessed variables (except for guild membership and exploration). Furthermore, some guilds were overrepresented in the self-selected samples.

Conclusions

Our results suggest that more proficient players or players more involved in the game may be more likely to participate in online surveys. Caution is needed in the interpretation of studies based on online surveys that used a self-selection recruitment procedure. Epidemiological evidence on the reduced representativeness of sample of online surveys is warranted.     

Searching scale space for activation in PET images

PET images of cerebral blood flow (CBF) in an activation study are usually smoothed to a resolution much poorer than the intrinsic resolution of the PET camera. This is done to reduce noise and to overcome problems caused by neuroanatomic variability among different subjects undertaking the same experimental task. In many studies the choice of this smoothing is arbitrarily fixed at about 20 mm FWHM, and the resulting statistical field or parametric map is searched for local maxima. Poline and Mazoyer [(1994): J Cereb Blood Flow Metab 14:690–699; (1994): IEEE Trans Med Imaging 13(4):702–710] have proposed a 4-D search over smoothing kernel widths as well as the usual three spatial dimensions. If the peaks are well separated then this makes it possible to estimate the size of regions of activation as well as their location. One of the main problems identified by Poline and Mazoyer is how to assess the significance of scale space peaks. In this paper we provide a solution for the case of pooled-variance Z-statistic images (Gaussian fields). Our main result is a unified P value for the 4-D local maxima that is accurate for searches over regions of any shape or size. Our results apply equally well to any Gaussian statistical field, such as those resulting from fMRI. © 1996 Wiley-Liss, Inc.     

Performance of opus immunoassays for thyroxine and beta-human chorionic gonadotrophin in serum

Two representative immunoassays for measuring thyroxine and β-subunit of human chorionic gonadotrophin in serum, using the Opus immunoassay analyzer, were evaluated by comparing them to the reference RIA for T4 and β-HCG enzyme immunoassay. Both assays were superior in accuracy and precision than the reference methods and exhibited good linearity throughout the concentration range needed for discriminating abnormally low and elevated concentrations from the established reference ranges of thyroxine and β-human chorionic gonadotrophin in serum. Correlation between the results of the Opus immunoassays and the reference assays for T4 and β-HCG was very good with correlation coefficients of 0.92 and 0.98, respectively. © 1996 Wiley-Liss, Inc.     

Evaluation of an optimized system for random amplified polymorphic DNA (RAPD)-analysis for genotypic mapping of Candida albicans strains

A simple, rapid, and cost-effective protocol has been developed for a PCR-based molecular typing method for Candida albicans, which includes the use of a commercially available medium (Chelex® 100 Resin) for DNA extraction and a single set of two arbitrarily chosen oligonucleotide (10 nt length) primers for random amplified DNA(RAPD)-analysis. The optimized parameters for the amplification components and conditions for the selected primer combination have been determined to avoid artifactual variation (absence/presence of bands) in RAPD banding patterns in repeated assays. The optimized RAPD-assay consistently generated DNA-patterns of 33 genetically unrelated C. albicans isolates that contained ten polymorphic markers in the non-artifactual banding patterns. The intralaboratory reproducibility of RAPD patterns was efficient and consistent provided the optimized amplification conditions were rigidly controlled. Interlaboratory reproducibility was tempered by slight variations in time of cyclers of different thermocyclers. In comparison, the RAPD assay was almost equal to restriction enzyme analysis (REA) (Eco RI digested chromosomal DNA) in discrimination, and the RAPD assay was able to group isolates of C. albicans that were untypable by REA. The protocol outlined for an optimized RAPD-assay of C. albicans has the potential to be widely useful epidemiological screening tool that can be easily applied in the clinical laboratory. © 1996 Wiley-Liss Inc.     

模糊马尔可夫场模型与图像分割新算法

本文建立模糊马尔可夫场模型,并提出基于模糊马尔可夫场的图像分割新算法。该算法同时处理模糊性和随机性,因此能有效获取图像的先验知识。在模糊马尔可夫场与待分割图像之间用经典的马尔可夫场关联。模糊马尔可夫场是经典马尔可夫场的推广,当模糊马尔可夫场失去模糊性时,它将退化为经典的马尔可夫场。给定图像,随即进行模糊化处理;以最大后验概率作为优化准则修正模糊马尔可夫场的隶属度;最后按照最大隶属度原则消除模糊性,从而得到图像的分割。该算法可以有效地虑除噪和消除部分容积效应,得到更为准确的分割结果。     

Illustration of the Importance of Adjustment for within- and between-Person Variability in Dietary Intake Surveys for Assessment of Population Risk of Micronutrient Deficiency/Excess Using an Example Data Set

Nutrition intervention decisions should be evidence based. Single 24-h recalls are often used for measuring dietary intake in large dietary studies. However, this method does not consider the day-to-day variation in populations’ diets. We illustrate the importance of adjustment of single 24-h recall data to remove within-person variation using the National Cancer Institute method to calculate usual intake when estimating risk of deficiency/excess. We used an example data set comprising a single 24-h recall in a total sample of 1326 1–<10-year-old children, and two additional recalls in a sub-sample of 11%, for these purposes. Results show that risk of deficiency was materially overestimated by the single unadjusted 24-h recall for vitamins B12, A, D, C and E, while risk of excess was overestimated for vitamin A and zinc, when compared to risks derived from usual intake. Food sources rich in particular micronutrients seemed to result in overestimation of deficiency risk when intra-individual variance is not removed. Our example illustrates that the application of the NCI method in dietary surveys would contribute to the formulation of more appropriate conclusions on risk of deficiency/excess in populations to advise public health nutrition initiatives when compared to those derived from a single unadjusted 24-h recall.     

Dual Thermo- and Photo-Responsive Micelles Based on Azobenzene-Containing Random Copolymer

Amphiphilic random copolymer poly(methacrylamido-azobenzene)-ran-poly(2-hydroxyethylacrylate) (PMAAAB-ran-PHEA) was synthesized via hydrolysis of poly(methacrylamido-azobenzene)-ran-poly[2-((2′-tetrahydropyranyl)oxy)ethylacrylate] (PMAAAB-ran-P(THP-HEA)), which was prepared by conventional radical polymerization. PMAAAB-ran-PHEA micelles were then prepared via dialysis method against water with DMF as solvent. The structure, morphology, size, and low critical solution temperature (LCST) of PMAAAB-ran-PHEA and its micelles were determined by ¹H-NMR, GPC, TEM, and DLS. The thermo- and photo-responsive behaviors of the resulting polymer micelles were investigated with Nile red as a fluorescence probe. The results showed that PMAAAB-ran-PHEA micelles were porous or bowl-shaped and its size was 135–150 nm, and its LCST was 55 °C when F_MAAAB of the random copolymer was 0.5351; the hydrophobicity of the micellar core was changed reversibly under the irradiation of UV light and visible light without release of Nile red or disruption of micelles; the size and solubilization capacity of the micelles were dependent on temperature, and Nile red would migrate for many times between the water phase and the micelles, and finally increasingly accumulated during the repeated heating and cooling processes.     

Simulation of Depth of Wear of Eco-Friendly Concrete Using Machine Learning Based Computational Approaches

To avoid time-consuming, costly, and laborious experimental tests that require skilled personnel, an effort has been made to formulate the depth of wear of fly-ash concrete using a comparative study of machine learning techniques, namely random forest regression (RFR) and gene expression programming (GEP). A widespread database comprising 216 experimental records was constructed from available research. The database includes depth of wear as a response parameter and nine different explanatory variables, i.e., cement content, fly ash, water content, fine and coarse aggregate, plasticizer, air-entraining agent, age of concrete, and time of testing. The performance of the models was judged via statistical metrics. The GEP model gives better performance with R² and ρ equals 0.9667 and 0.0501 respectively and meet with the external validation criterion suggested in the previous literature. The k-fold cross-validation also verifies the accurateness of the model by evaluating R², RSE, MAE, and RMSE. The sensitivity analysis of GEP equation indicated that the time of testing is the influential parameter. The results of this research can help the designers, practitioners, and researchers to quickly estimate the depth of wear of fly-ash concrete thus shortening its ecological susceptibilities that push to sustainable and faster construction from the viewpoint of environmentally friendly waste management.