Decreasing Sample Size Research Articles

Monitoring Passerine Reproduction by Constant Effort Ringing: Evaluation of the Efficiency of Trend Detection

The Dutch Constant Effort Site (CES) programme has been operating since 1994 and is especially designed for the analysis of demographic parameters. Currently, it works with 40 active mist-netting sites and has a database with more than 250,000 records at its disposal. Here, we ask whether the effort invested in the programme is appropriate to detect temporal trends of productivity of passerine bird populations across The Netherlands. We specifically ask if less effort would produce the same results or if the number of CESs should be augmented. To evaluate these questions we used a resampling approach in which we decreased sample size in steps of five and iterated resampling 1000 times for each step, thus simulating CES programmes in which fewer sites were operated. For the twenty most abundant species and for each sample size, linear regressions of the productivity index (a logistic generalized linear model of the proportion of captured juvenile birds) on year were compared with the regression obtained using the complete records. The proportion of samples that yielded significant positive or negative slopes was determined, as well. For the majority of species without significant temporal trends (18), the proportions of significant slopes at smaller sample sizes were lower than 20%, indicating a moderate risk of committing Type I errors (detecting a negative or positive trend although productivity did not change over time). For the Garden Warbler Sylvia borin, which showed a significant positive productivity trend, the probability of committing Type II errors (not detecting existing trends) increased rapidly with decreasing sample size. We conclude that the Dutch CES programme works with a sufficient number of sites to detect reliable temporal trends for most of the more abundant passerine species. However, increasing the number of sites would allow for a more secure determination of productivity trends for those species that currently show ambiguous results (Reed Warbler Acrocephalus scirpaceus, Willow Warbler Phylloscopus trochilus, Willow Tit Parus montanus).

Microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor – Part I: Changes in chemical composition, density and equilibrium moisture content

Abstract Fungal degradation alters the microstructure of wood and its physical and chemical properties are also changed. While these changes are well investigated as a function of mass loss, mass density loss and changes in equilibrium moisture content are not well elucidated. The physical and chemical alterations are crucial when linking microstructural characteristics with macroscopic mechanical properties. In the present article, a consistent set of physical, chemical and mechanical characteristics is presented, which were measured on the same sample before and after fungal degradation. In the first part of this two-part contribution, elucidating microstructure/stiffness-relationships of degraded wood, changes in physical and chemical data are presented, which were collected from specimens of Scots pine (Pinus sylvestris) sapwood degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks degradation time. A comparison of mass loss with corresponding mass density loss demonstrated that mass loss entails two effects: firstly, a decrease in sample size (more pronounced for G. trabeum), and secondly, a decrease of mass density within the sample (more pronounced for T. versicolor). These two concurrent effects are interrelated with sample size and shape. Hemicelluloses and cellulose are degraded by G. trabeum, while T. versicolor was additionally able to degrade lignin. In particular because of the breakdown of hemicelluloses and paracrystalline parts of cellulose, the equilibrium moisture content of degraded samples is lower than that in the initial state.

Novel microfocus X-ray sources for high-pressure crystallography

Beam Characteristics of the IμS The Ag-IμS delivers a focused and monochromatic X-ray beam with a FWHM of 0.09 mm in the image focus. In contrast to the typical top-hat shaped beam profile that is produced by sources coupled to a flat graphite monochromator, the beam profile from the IμS has a symmetrical Gaussian-shaped intensity distribution. As a consequence, the flux density increases with decreasing sample size (Fig. 1), thus leading to strong diffracted intensities especially for small samples. Furthermore, the convergent beam from the IμS reduces the background of the data by minimizing the scattering from peripherals, such as conventional crystal mounts or gaskets. The integrated intensity of the original Ag-IμS, which is available since 2009, is at least about three times higher than the intensity of a 1.5 kW Ag sealed tube system. The new Ag-IμSHigh Brilliance has an improved X-ray optical design that results in a further intensity gain of 50% when compared to the original Ag-IμS.

OPPORTUNITY : a large-scale randomized clinical trial of growth hormone in hemodialysis patients

Adult maintenance hemodialysis (MHD) patients experience high mortality and morbidity and poor quality of life (QoL). Markers of protein-energy wasting are associated with these poor outcomes. The OPPORTUNITY™ Trial examined whether recombinant human growth hormone (hGH) reduces mortality in hypoalbuminemic MHD patients. Secondary end points were effects on number of hospitalizations, cardiovascular events, lean body mass (LBM), serum proteins, exercise capacity, QoL and adverse events. We performed a randomized, double-blind, placebo-controlled, multicenter multinational trial stratified for diabetic status. Clinically, stable adult MHD patients with serum albumin <4.0 g/dL were randomized to subcutaneous injections of hGH, 20 μg/kg/day, or placebo. Planned treatment duration was 24 months for 2500 patients. The trial was terminated early due to slow recruitment. Seven hundred and twelve patients were randomized until trial termination; 695 patients received at least one dose of trial medication. Mean treatment duration was 20 weeks (no completers). There were no differences between groups in all-cause mortality, cardiovascular morbidity or mortality, serum albumin, LBM, physical exercise capacity or QoL. The hGH group, compared to placebo, displayed a reduction in body weight, total body fat, serum high-sensitivity C-reactive protein and possibly homocysteine and an increase in serum high-density lipoprotein-cholesterol and transferrin levels. Although the OPPORTUNITY™ Trial was terminated early, treatment with hGH, compared to placebo, improved certain cardiovascular risk factors but did not reduce mortality, cardiovascular events or improve nutritional factors or QoL. The power for showing differences was substantially reduced due to the marked decrease in treatment duration and sample size.

Yielding and Irreversible Deformation below the Microscale: Surface Effects and Non-Mean-Field Plastic Avalanches

Nanoindentation techniques recently developed to measure the mechanical response of crystals under external loading conditions reveal new phenomena upon decreasing sample size below the microscale. At small length scales, material resistance to irreversible deformation depends on sample morphology. Here we study the mechanisms of yield and plastic flow in inherently small crystals under uniaxial compression. Discrete structural rearrangements emerge as a series of abrupt discontinuities in stress-strain curves. We obtain the theoretical dependence of the yield stress on system size and geometry and elucidate the statistical properties of plastic deformation at such scales. Our results show that the absence of dislocation storage leads to crucial effects on the statistics of plastic events, ultimately affecting the universal scaling behavior observed at larger scales.

Field permeability at shallow depth in a compacted fill

This paper presents a series of field double-ring infiltration tests (DRTs) for investigating the hydraulic conductivity of a compacted silty clay fill that contains some desiccation cracks. These field tests were conducted at three different depths in the fill, to characterise the variations of conductivity with depth. The hydraulic conductivity of the fill was also measured in the laboratory on block samples using a three-directional permeability cell (sample size: 200 mm × 200 mm × 200 mm) and a one-dimensional permeameter (sample size: 70 mm in diameter and 45 mm high). A perched water table was detected in the fill using tensiometers shortly after the start of each DRT, showing the presence of preferential flow paths in the fill. The hydraulic conductivity decreases with increasing depth. The larger hydraulic conductivity of the surface soil indicates the possible presence of macropores and cracks at shallow depths of the fill. The coefficients of variation of the hydraulic conductivity measured from the DRTs (influence volume: 300 mm in diameter and 450 mm high) and the three-directional permeability cell tests are smaller than those measured from the small-size, one-dimensional permeameter tests. The variability of the measured hydraulic conductivity increases as the sample size decreases.

Length scale effects on the shear localization process in metallic glasses: A theoretical and computational study

Some recent experiments on sub-micron and nano-sized metallic glass (amorphous alloy) specimens have shown that the shear localization process becomes more stable and less catastrophic when compared to the response exhibited by large sample sizes. This leads to the discovery that the shear localization process and fracture can be delayed by decreasing sample volume. In this work we develop a non-local and finite-deformation-based constitutive model using thermodynamic principles and the theory of micro-force balance to study the causes for the aforementioned observations. The constitutive model has also been implemented into a commercially available finite-element program by writing a user-material subroutine. With the aid of finite-element simulations, our constitutive model predicts that metallic glass samples have the intrinsic ability to exhibit: (a) the delaying of (catastrophic) shear localization with decreasing sample size, and (b) homogeneous deformation behavior for sample volumes smaller than the shear band nucleus. The cause for the observations listed above is the increasing influence of a non-local interaction stress with decreasing sample volume. This interaction stress has energetic origins and it affects plastic deformation due to the strong coupling between plastic shearing and free-volume generation. Akin to strain-gradient plasticity theory, the role of the interaction stress is to strengthen the material at locations where the defect density/free volume is higher compared to the rest of metallic glass sample.

Genome-based prediction of testcross values in maize

This is the first large-scale experimental study on genome-based prediction of testcross values in an advanced cycle breeding population of maize. The study comprised testcross progenies of 1,380 doubled haploid lines of maize derived from 36 crosses and phenotyped for grain yield and grain dry matter content in seven locations. The lines were genotyped with 1,152 single nucleotide polymorphism markers. Pedigree data were available for three generations. We used best linear unbiased prediction and stratified cross-validation to evaluate the performance of prediction models differing in the modeling of relatedness between inbred lines and in the calculation of genome-based coefficients of similarity. The choice of similarity coefficient did not affect prediction accuracies. Models including genomic information yielded significantly higher prediction accuracies than the model based on pedigree information alone. Average prediction accuracies based on genomic data were high even for a complex trait like grain yield (0.72-0.74) when the cross-validation scheme allowed for a high degree of relatedness between the estimation and the test set. When predictions were performed across distantly related families, prediction accuracies decreased significantly (0.47-0.48). Prediction accuracies decreased with decreasing sample size but were still high when the population size was halved (0.67-0.69). The results from this study are encouraging with respect to genome-based prediction of the genetic value of untested lines in advanced cycle breeding populations and the implementation of genomic selection in the breeding process.

Influence of decreased sample size on cone calorimeter results

SUMMARYCone calorimeter sample size sensitivity and the influence of sample size on the results were studied in order to investigate the possibility to use smaller samples than prescribed by the standard. The influence of the position of the sample on the sample holder of the decreased samples was also studied. Samples of birch plywood, industrial two‐component polyurethane adhesive and polypropylene wax were tested. The results from standard size sample experiments, 100 cm 2, and decreased sample size, 50 and 25 cm2, were compared, in order to investigate the sample size influence on the results. The experiments were performed using an external heat flux of 50kW/ m2. The results show differences between the sample types. The measured heat release rates for plywood and polyurethane adhesive indicate that the sample size is possible to down‐scale, while the polypropylene wax results show the opposite. All sample types and sizes show constant results for the effective heat of combustion, indicating down‐scalability. For in‐house testing and screening of materials, downscaling can be used for most sample types. However, results from experiments carried out with decreased sample size should not be compared to results from experiments executed according to the standard procedure. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Salmonella Enteritidis Surveillance by Egg Immunology: Impact of the Sampling Scheme on the Release of Contaminated Table Eggs

Design of surveillance programs to detect infections could benefit from more insight into sampling schemes. We address the effect of sampling schemes for Salmonella Enteritidis surveillance in laying hens. Based on experimental estimates for the transmission rate in flocks, and the characteristics of an egg immunological test, we have simulated outbreaks with various sampling schemes, and with the current boot swab program with a 15-week sampling interval. Declaring a flock infected based on a single positive egg was not possible because test specificity was too low. Thus, a threshold number of positive eggs was defined to declare a flock infected, and, for small sample sizes, eggs from previous samplings had to be included in a cumulative sample to guarantee a minimum flock level specificity. Effectiveness of surveillance was measured by the proportion of outbreaks detected, and by the number of contaminated table eggs brought on the market. The boot swab program detected 90% of the outbreaks, with 75% fewer contaminated eggs compared to no surveillance, whereas the baseline egg program (30 eggs each 15 weeks) detected 86%, with 73% fewer contaminated eggs. We conclude that a larger sample size results in more detected outbreaks, whereas a smaller sampling interval decreases the number of contaminated eggs. Decreasing sample size and interval simultaneously reduces the number of contaminated eggs, but not indefinitely: the advantage of more frequent sampling is counterbalanced by the cumulative sample including less recently laid eggs. Apparently, optimizing surveillance has its limits when test specificity is taken into account.

Identification of Differential Item Functioning in Assessment Booklet Designs With Structurally Missing Data

The Mantel—Haenszel procedure is a popular technique for determining items that may exhibit differential item functioning (DIF). Numerous studies have focused on the strengths and weaknesses of this procedure, but few have focused the performance of the Mantel—Haenszel method when structurally missing data are present as a result of test booklet design. The current research compares the Type I error rate, power rate, and accuracy of DIF statistics when using the Mantel—Haenszel methods to detect DIF in three different test booklet designs that produce sparse data. Data were simulated for three different total sample sizes, fully crossed with three different test lengths, and two focal to reference group ratios. In general, the Mantel—Haenszel procedure was not adversely affected by sparseness of data under any of the booklet designs considered when sample size was adequately large. As sample sizes decrease, both the amount of sparseness and features of the booklet design may influence the ability to detect DIF.

Improved SNR of Magnetic Resonance Microimaging using a Cooled Resonance Circuit at 0.3T

Because it is noninvasive, magnetic resonance microimaging (MRMI) can be used for 3-dimensional measurement of living tissues for cell engineering. Thermal noise in the resonance circuit of the radiofrequency (RF) system of the MRMI cannot become ignored as the signal diminishes in accordance with decreasing sample size, and cooling the RF coil of the receiver circuit can effectively reduce thermal noise. We used a low temperature normal conductor circuit to reduce noise and confirmed improved signal-to-noise ratio for a conventional microimaging system at low B(0) field (0.3T) with low cost.

Critical Supercurrents and Self-Organization in Quantum Hall Bilayers

We present a theory of interlayer tunneling in a disordered quantum Hall bilayer at total filling factor one, allowing for the effect of static vortices. In agreement with recent experiments [Phys. Rev. B 80, 165120 (2009); Phys. Rev. B 78, 075302 (2008)], we find that the critical current is proportional to the sample area and is comparable in magnitude to observed values. This reflects the formation of a Bean critical state as a result of current injection at the boundary. We predict a crossover to a critical current proportional to the square-root of the area in smaller samples. We also predict a peak in the critical current as the electron density varies at fixed layer separation.

Quantification of recurrence volumes after endovascular treatment of cerebral aneurysm as surrogate endpoint for treatment stability

New coils with unproven clinical benefit enlarge the armamentarium for endovascular aneurysm treatment continuously. Large patient numbers needed to detect benefits of such new techniques prevent timely evaluation of efficacy. We propose measuring the volume of aneurysm recurrences as surrogate endpoint for coil stability. We hypothesize that this method allows detecting effects of new materials with reduced sample sizes in comparison to conventional studies with dichotomous endpoints. Institutional review board approval and informed consent were obtained. Fifty-nine patients with decreasing aneurysm size and at least two available follow-up time-of-flight magnetic resonance angiographies (ToF-MRAs) were included. Newly developed software for measuring aneurysm volume differences based on ToF-MRA images was used. Based on the observed recurrence volumes and retreatment rates, the sample size for future studies comparing standard versus "new coils" were calculated. Mean recurrence volume was 38.92μl (SD110.85μl). To show a 50% reduction of retreatment rate to control (p = 0.05; power 80%) in a regular study (dichotomous endpoint), the required sample size would be n = 356 compared with n = 78 if using the continuous surrogate endpoint "recurrence volume". When extrapolating our data to data given in the literature, sample sizes could be reduced from n = 948 to n = 74 without loss of statistical power. Further studies on new materials using volumetric analysis based on ToF-MRA as surrogate endpoint could substantially decrease sample size and allow a more timely assessment of possible benefit of new materials with a fraction of the cost.

Sample size determination in clinical trials with multiple co‐primary binary endpoints

Clinical trials often employ two or more primary efficacy endpoints. One of the major problems in such trials is how to determine a sample size suitable for multiple co-primary correlated endpoints. We provide fundamental formulae for the calculation of power and sample size in order to achieve statistical significance for all the multiple primary endpoints given as binary variables. On the basis of three association measures among primary endpoints, we discuss five methods of power and sample size calculation: the asymptotic normal method with and without continuity correction, the arcsine method with and without continuity correction, and Fisher's exact method. For all five methods, the achieved sample size decreases as the value of association measure increases when the effect sizes among endpoints are approximately equal. In particular, a high positive association has a greater effect on the decrease in the sample size. On the other hand, such a relationship is not very strong when the effect sizes are different.

Use of Electron Microscopy in Core Biopsy Diagnosis of Oncocytic Renal Tumors

The distinction between oncocytoma and chromophobe renal cell carcinoma, important clinically, may be challenging, especially as the tissue sample size decreases. Ancillary studies can be helpful, although subject to interpretation and sample variability. The aim of this study was to examine the value of electron microscopy in differentiating between oncocytoma and chromophobe renal cell carcinoma on formalin fixed paraffin embedded needle core biopsies. Twenty renal needle core biopsies were evaluated. Despite formalin fixation and paraffin embedding, the classic ultrastructural features of these neoplasms were retained, revealing 80% sensitivity and 100% specificity by initial work-up.

Evaluation of shortwave infrared atmospheric correction for ocean color remote sensing of Chesapeake Bay

The NASA Moderate Resolution Imaging Spectroradiometer onboard the Aqua platform (MODIS-Aqua) provides a viable data stream for operational water quality monitoring of Chesapeake Bay. Marine geophysical products from MODIS-Aqua depend on the efficacy of the atmospheric correction process, which can be problematic in coastal environments. The operational atmospheric correction algorithm for MODIS-Aqua requires an assumption of negligible near-infrared water-leaving radiance, nLw(NIR). This assumption progressively degrades with increasing turbidity and, as such, methods exist to account for non-negligible nLw(NIR) within the atmospheric correction process or to use alternate radiometric bands where the assumption is satisfied, such as those positioned within shortwave infrared (SWIR) region of the spectrum. We evaluated a decade-long time-series of nLw(λ) from MODIS-Aqua in Chesapeake Bay derived using NIR and SWIR bands for atmospheric correction. Low signal-to-noise ratios (SNR) for the SWIR bands of MODIS-Aqua added noise errors to the derived radiances, which produced broad, flat frequency distributions of nLw(λ) relative to those produced using the NIR bands. The SWIR approach produced an increased number of negative nLw(λ) and decreased sample size relative to the NIR approach. Revised vicarious calibration and regional tuning of the scheme to switch between the NIR and SWIR approaches may improve retrievals in Chesapeake Bay, however, poor SNR values for the MODIS-Aqua SWIR bands remain the primary deficiency of the SWIR-based atmospheric correction approach.

Porous iron pellets for AMS 14C analysis of small samples down to ultra-microscale size (10–25μgC)

Abstract We developed the use of a porous iron pellet as a catalyst for AMS 14C analysis of small samples down to ultra-microscale size (10–25 μgC). It resulted in increased and more stable beam currents through our HVEE 4130 14C AMS system, which depend smoothly on the sample size. We find that both the expected decrease of oxalic acid standards and increase of backgrounds with decreasing sample size, due to increasing influence of contamination, are reproducible. Using a mass-dependent background correction for dead (1.0 ± 0.4 μgC) and modern (0.25 ± 0.10 μgC) contamination, we obtain reliable results for small samples down to 10 μgC and possibly smaller. Due to our low graphitization yield for ultra-small samples (increases from 40% to 80% on average with sample size), we measured graphite standards as small as 3 μgC. The standard deviation of the corrected activity is about 5% for a 10-μgC HOxII standard. Here we report the iron pellet technique, which is new to the best of our knowledge. It is generally applicable for AMS 14C laboratories that want to measure small samples down to ultra-microscale size. As an illustrative test-case, we analyze 14C data for IAEA-C5, C7 and C8 samples with masses ranging from 15 to 300 μgC.

Strong crystal size effect on deformation twinning

Deformation twinning in crystals is a highly coherent inelastic shearing process that controls the mechanical behaviour of many materials, but its origin and spatio-temporal features are shrouded in mystery. Using micro-compression and in situ nano-compression experiments, here we find that the stress required for deformation twinning increases drastically with decreasing sample size of a titanium alloy single crystal, until the sample size is reduced to one micrometre, below which the deformation twinning is entirely replaced by less correlated, ordinary dislocation plasticity. Accompanying the transition in deformation mechanism, the maximum flow stress of the submicrometre-sized pillars was observed to saturate at a value close to titanium's ideal strength. We develop a 'stimulated slip' model to explain the strong size dependence of deformation twinning. The sample size in transition is relatively large and easily accessible in experiments, making our understanding of size dependence relevant for applications.

Is There a Size Limit for Cosmopolitan Distribution in Free-Living Microorganisms? A Biogeographical Analysis of Testate Amoebae from Polar Areas

A long-standing debate in microbial ecology is the extent to which free-living microorganisms exhibit cosmopolitan distributions. We use a comparison of testate amoebae communities in cold "polar" locations (Arctic, Antarctic, and Tibet) to investigate how a microorganism's size affects its probability of having a cosmopolitan distribution. We show that the probability a given taxa being reported in all three locations increases as testate size decreases. Likewise, excluding those testates found only in Tibet, very small testates (<20 microm) are more likely to occur in both the Arctic and Antarctic than in either of these poles alone. Attempting to correct for phylogeny reduces the number of statistically significant relationships--both because of decreased sample size and potentially real phylogenetic patterns, although some size-dependent effects were still apparent. In particular, taxa found in both the Arctic and Antarctic poles were significantly smaller than congeneric taxa found only in Tibet. This pattern may in part be due to habitat effects, with the Tibetan samples being more likely to have come from aquatic sites which may be more suitable for larger taxa. Overall, our analysis suggests that, at least within testate amoebae, a cosmopolitan distribution becomes increasingly common as median taxon size decreases.