Analyzing Group Level Effects with Clustered Data Using Taylor Series Linearization

Clustered data (e.g., students within schools) are often analyzed in educational research where data are naturally nested. As a consequence, multilevel modeling (MLM) has commonly been used to study the contextual or group-level (e.g., school) effects on individual outcomes. The current study investigates the use of an alternative procedure to MLM: regression using Taylor series linearization (TSL) variance estimation. Despite the name, regressions using TSL are straightforward to conduct, can yield consistent and unbiased estimates and standard errors (given the appropriate conditions), and can be performed using a variety of commercially- and freely-available statistical software. I analyze a subsample of the High School and Beyond (HSB) dataset using MLM, regression using TSL, and ordinary least squares regression and compare results. In addition, 12,000 random samples are drawn from the HSB dataset of varying level-one and level-two sample sizes in order to compute biases in standard errors based on the different conditions. Sample R and SAS syntax showing how to run regressions using TSL are provided Accessed 5,000 times on https://pareonline.net from November 11, 2014 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right

Using Instrumental Variable Estimation to Evaluate Randomized Experiments with Imperfect Compliance

Among econometricians, instrumental variable (IV) estimation is a commonly used technique to estimate the causal effect of a particular variable on a specified outcome. However, among applied researchers in the social sciences, IV estimation may not be well understood. Although there are several IV estimation primers from different fields, most manuscripts are not readily accessible by researchers who may only be familiar with regression-based techniques. The manuscript provides a conceptual framework of why and how IV works in the context of evaluating treatment effects using randomized evaluations. I discuss the issue of imperfect treatment compliance, explain the logic of IV estimation, provide a sample dataset, and syntax for conducting IV analysis using R. A goal of the current manuscript is to demystify the use of IV estimation and make evaluation studies that use this technique more readily understood by researchers. Accessed 3,266 times on https://pareonline.net from February 24, 2018 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right

Use of 2d-video Disdrometer to Derive Mean Density-size and Ze-SR Relations: Four Snow Cases from the Light Precipitation Validation Experiment

The application of the 2D-video disdrometer to measure fall speed and snow size distribution and to derive liquid equivalent snow rate, mean density-size and reflectivity-snow rate power law is described. Inversion of the methodology proposed by Bhm provides the pathway to use measured fall speed, area ratio and '3D' size measurement to estimate the mass of each particle. Four snow cases from the Light Precipitation Validation Experiment are analyzed with supporting data from other instruments such as Precipitation Occurrence Sensor System (POSS), Snow Video Imager (SVI), a network of seven snow gauges and three scanning C9 band radars. The radar-based snow accumulations using the 2DVD-derived Ze-SR relation are in good agreement with a network of seven snow gauges and outperform the accumulations derived from a climatological Ze-SR relation used by the Finnish Meteorological Institute (FMI). The normalized bias between radar-derived and gauge accumulation is reduced from 96% when using the fixed FMI relation to 28% when using the Ze-SR relations based on 2DVD data. The normalized standard error is also reduced significantly from 66% to 31%. For two of the days with widely different coefficients of the Ze-SR power law, the reflectivity structure showed significant differences in spatial variability. Liquid water path estimates from radiometric data also showed significant differences between the two cases. Examination of SVI particle images at the measurement site corroborated these differences in terms of unrimed versus rimed snow particles. The findings reported herein support the application of Bhm's methodology for deriving the mean density-size and Ze-SR power laws using data from 2D-video disdrometer

Controlling magnetic order and quantum disorder in molecule-based magnets

We investigate the structural and magnetic properties of two molecule-based magnets synthesized from the same starting components. Their different structural motifs promote contrasting exchange pathways and consequently lead to markedly different magnetic ground states. Through examination of their structural and magnetic properties we show that [Cu(pyz)(H2O)(gly)2](ClO4)2 may be considered a quasi-one-dimensional quantum Heisenberg antiferromagnet whereas the related compound [Cu(pyz)(gly)](ClO4), which is formed from dimers of antiferromagnetically interacting Cu2+ spins, remains disordered down to at least 0.03 K in zero field but shows a field-temperature phase diagram reminiscent of that seen in materials showing a Bose-Einstein condensation of magnons

The templated growth of a chiral transition metal chalcogenide

We demonstrate that an intrinsically chiral, high Miller index surface of an achiral metal can be used to template the enantioselective growth of chiral transition metal chalcogenide films. Specifically, Cu(643)R can be used as a template for the enantioselective growth of a chiral copper telluride alloy surface. Beyond a critical alloy thickness the chiral influence of the Cu(643)R surface diminishes and an achiral surface forms. Our work demonstrates a new method of producing chiral transition metal chalcogenide surfaces, with potential applications in the study of structurally chiral topological insulators

Evaluation on the resistance to aphids of wheat germplasm resources in China

A collection of more than 200 wheat lines from the main wheat-producing areas of China was evaluated for resistance to wheat aphids, using fuzzy recognition technique in five field experiments over 2 years. The results show that susceptibility to wheat aphids was exhibited in most of the lines tested, and no immune and highly resistant lines to wheat aphids was observed. The average percentage of wheat germplasm lines with resistant, lowly susceptible, moderately susceptible and highly susceptible to aphid were 9.30, 23.15, 42.32, and 25.23%, respectively. 5 moderately resistant wheat germplasm lines to wheat aphids (Lantian18, Lantian20, Lantian22, Lantian00-30 and Shanmai175) were found in Jiangyou experimental station in 2009. More importantly, 2 wheat germplasm lines (Lantian20, Lantian22) with the continuous resistance to wheat aphid in the five experimental stations over 2 years were discovered. Although, resistance of wheat germplasm lines had a close relation to their genetics and inheritance, we also found that the resistance of the same wheat germplasm lines was varied in different experimental stations. It would be helpful to make wheat germplasm selections for breeding programs, especially if they have unique genes that may provide resistance to future biotypes of wheat aphids. A valuable method for evaluating the potential of aphid-resistance for wheat germplasm lines was also confirmed.Key words: Wheat germplasm lines, aphid, resistance identification

Bone mineral density and content during weight cycling in female rats: effects of dietary amylase-resistant starch

<p>Abstract</p> <p>Background</p> <p>Although there is considerable evidence for a loss of bone mass with weight loss, the few human studies on the relationship between weight cycling and bone mass or density have differing results. Further, very few studies assessed the role of dietary composition on bone mass during weight cycling. The primary objective of this study was to determine if a diet high in amylase-resistant starch (RS₂), which has been shown to increase absorption and balance of dietary minerals, can prevent or reduce loss of bone mass during weight cycling.</p> <p>Methods</p> <p>Female Sprague-Dawley (SD) rats (n = 84, age = 20 weeks) were randomly assigned to one of 6 treatment groups with 14 rats per group using a 2 × 3 experimental design with 2 diets and 3 weight cycling protocols. Rats were fed calcium-deficient diets without RS₂(controls) or diets high in RS₂(18% by weight) throughout the 21-week study. The weight cycling protocols were weight maintenance/gain with no weight cycling, 1 round of weight cycling, or 2 rounds of weight cycling. After the rats were euthanized bone mineral density (BMD) and bone mineral content (BMC) of femur were measured by dual energy X-ray absorptiometry, and concentrations of calcium, copper, iron, magnesium, manganese, and zinc in femur and lumbar vertebrae were determined by atomic absorption spectrophotometry.</p> <p>Results</p> <p>Rats undergoing weight cycling had lower femur BMC (p < 0.05) and marginally lower BMD (p = 0.09) than rats not undergoing weight cycling. In comparison to controls, rats fed RS₂had higher femur BMD (p < 0.01) and BMC (p < 0.05), as well as higher values for BMD and BMC measured at the distal end (p < 0.001 and p < 0.01) and femoral neck (p < 0.01 and p < 0.05). Consistent with these findings, RS₂-fed rats also had higher femur calcium (p < 0.05) and magnesium (p < 0.0001) concentrations. They also had higher lumbar vertebrae calcium (p < 0.05) and magnesium (p < 0.05) concentrations.</p> <p>Conclusion</p> <p>Weight cycling reduces bone mass. A diet high in RS₂can minimize loss of bone mass during weight cycling and may increase bone mass in the absence of weight cycling.</p

Spitzer observations of extended Lyman-alpha Clouds in the SSA22 field

We present the results of a Spitzer IRAC and MIPS 24 micron study of extended Lyman-alpha clouds (or Lyman-alpha Blobs, LABs) within the SSA22 filamentary structure at z = 3.09. We detect 6/26 LABs in all IRAC filters, four of which are also detected at 24 micron, and find good correspondence with the 850 micron measurements of Geach et al. 2005. An analysis of the rest-frame ultraviolet, optical, near- and mid-infrared colors reveals that these six systems exhibit signs of nuclear activity (AGN)and/or extreme star formation. Notably, they have properties that bridge galaxies dominated by star formation (Lyman-break galaxies; LBGs) and those with AGNs (LBGs classified as QSOs). The LAB systems not detected in all four IRAC bands, on the other hand, are, as a group, consistent with pure star forming systems, similar to the majority of the LBGs within the filament. These results indicate that the galaxies within LABs do not comprise a homogeneous population, though they are also consistent with scenarios in which the gas halos are ionized through a common mechanism such as galaxy-scale winds driven by the galaxies within them, or gravitational heating of the collapsing cloud itself.Comment: 11 pages, 6 figures, accepted for publication in the Astrophysical Journa

Do patient characteristics matter when calculating sample size for eczema clinical trials?

BackgroundThe Patient-Oriented Eczema Measure (POEM) is the core outcome instrument recommended for measuring patient-reported atopic eczema symptoms in clinical trials. To ensure that the statistical significance of clinical trial results is meaningful, trials are often designed by specifying the target difference in the primary outcome as part of the sample size calculation. One method used to specify the target difference is a score that corresponds to a standardized effect size.Objectivesto assess how the standardized effect size of POEM scores vary across age, gender, ethnicity and disease severity.MethodsThis study combined data from five UK-based randomized clinical trials of eczema treatments in order to assess differences in self-reported eczema symptoms (POEM) corresponding to a standardized effect size (0.5 SD of baseline POEM scores) across age, gender, ethnicity and disease severity.ResultsPOEM scores corresponding to 0.5 SD(baseline) were remarkably consistent across participants of varying ages, gender, ethnicity and disease severity from datasets of five UK trials in children (range 2.99–3.45).ConclusionsThis study provides information that can support those designing clinical trials to determine their sample size and can aid individuals interpreting trial results. Further exploration of differences in populations beyond the United Kingdom is needed

Decadal changes of the Western Arabian sea ecosystem

Historical data from oceanographic expeditions and remotely sensed data on outgoing longwave radiation, temperature, wind speed and ocean color in the western Arabian Sea (1950–2010) were used to investigate decadal trends in the physical and biochemical properties of the upper 300 m. 72 % of the 29,043 vertical profiles retrieved originated from USA and UK expeditions. Increasing outgoing longwave radiation, surface air temperatures and sea surface temperature were identified on decadal timescales. These were well correlated with decreasing wind speeds associated with a reduced Siberian High atmospheric anomaly. Shoaling of the oxycline and nitracline was observed as well as acidification of the upper 300 m. These physical and chemical changes were accompanied by declining chlorophyll-a concentrations, vertical macrofaunal habitat compression, declining sardine landings and an increase of fish kill incidents along the Omani coast