Source Of Variability In Results Research Articles

Uncertain Environmental Footprint of Current and Future Battery Electric Vehicles.

The future environmental impacts of battery electric vehicles (EVs) are very important given their expected dominance in future transport systems. Previous studies have shown these impacts to be highly uncertain, though a detailed treatment of this uncertainty is still lacking. We help to fill this gap by using Monte Carlo and global sensitivity analysis to quantify parametric uncertainty and also consider two additional factors that have not yet been addressed in the field. First, we include changes to driving patterns due to the introduction of autonomous and connected vehicles. Second, we deeply integrate scenario results from the IMAGE integrated assessment model into our life cycle database to include the impacts of changes to the electricity sector on the environmental burdens of producing and recharging future EVs. Future EVs are expected to have 45-78% lower climate change impacts than current EVs. Electricity used for charging is the largest source of variability in results, though vehicle size, lifetime, driving patterns, and battery size also strongly contribute to variability. We also show that it is imperative to consider changes to the electricity sector when calculating upstream impacts of EVs, as without this, results could be overestimated by up to 75%.

Short-term changes in ambient particulate matter and risk of stroke: a systematic review and meta-analysis.

BackgroundStroke is a leading cause of death and long‐term disability in the United States. There is a well‐documented association between ambient particulate matter air pollution (PM) and cardiovascular disease morbidity and mortality. Given the pathophysiologic mechanisms of these effects, short‐term elevations in PM may also increase the risk of ischemic and/or hemorrhagic stroke morbidity and mortality, but the evidence has not been systematically reviewed.Methods and ResultsWe provide a comprehensive review of all observational human studies (January 1966 to January 2014) on the association between short‐term changes in ambient PM levels and cerebrovascular events. We also performed meta‐analyses to evaluate the evidence for an association between each PM size fraction (PM2.5, PM10, PM2.5‐10) and each outcome (total cerebrovascular disease, ischemic stroke/transient ischemic attack, hemorrhagic stroke) separately for mortality and hospital admission. We used a random‐effects model to estimate the summary percent change in relative risk of the outcome per 10‐μg/m3 increase in PM.ConclusionsWe found that PM2.5 and PM10 are associated with a 1.4% (95% CI 0.9% to 1.9%) and 0.5% (95% CI 0.3% to 0.7%) higher total cerebrovascular disease mortality, respectively, with evidence of inconsistent, nonsignificant associations for hospital admission for total cerebrovascular disease or ischemic or hemorrhagic stroke. Current limited evidence does not suggest an association between PM2.5‐10 and cerebrovascular mortality or morbidity. We discuss the potential sources of variability in results across studies, highlight some observations, and identify gaps in literature and make recommendations for future studies.

Understanding sorting grid and codend size selectivity of Greenland halibut (Reinhardtius hippoglossoides)

We studied the size selectivity of Greenland halibut (Reinhardtius hippoglossoides) using the fish morphology-based FISHSELECT methodology, size selectivity data from two sets of sea trials carried out in the Barents Sea and the Norwegian Sea, and historical selectivity data collected for this species from 1981 onwards. When compared, the historical codend size selectivity data fitted well with the selectivity predictions from the FISHSELECT analyses. The historical grid selectivity data and the results from the two sea trials showed considerably lower L50 values than what would be expected from the morphological-based limit estimated by FISHSELECT. The size selectivity results obtained from the analysis of the two sea trials differed significantly, even though they were conducted using grid sections with similar bar spacing that previously were shown to have similar selective properties for other species. The differences were not caused by differences in the ability of the fish to contact the grid. Instead, these differences can be explained by differences in the ability of the fish to turn before they attack the grid. In earlier grid selectivity studies, the influence of angle of attack (θ) was not quantified. We show that the ability to contact the grid with a more or less optimal θ differs between individuals. This is important to consider in grid selectivity studies for flatfish species such as Greenland halibut because it can potentially influence results considerably and therefore can be a source of variability in results between cruises.

Spirometry: Don't Blow It!

Spirometry is a useful test of pulmonary function and can be safely performed in a variety of clinical situations. Although the technique for performing the maneuver is straightforward, there are many sources of variability in results. Specific criteria must be met in order for the test to be considered valid. For the best results, proper instruction and coaching is essential, and patient understanding and effort must be maximized. Appropriate interpretation of spirometry requires several steps, including recognition and reporting of technically sound maneuvers, comparison to an appropriate reference population, and finally application of a well-developed interpretation scheme utilized in the context of patient symptoms and findings. Failure at any point along this path from performance to interpretation can yield misleading results that may ultimately poorly impact patient care. A clear understanding by the provider of proper coding and billing for spirometry is necessary to receive appropriate reimbursement from payers.

Visual field defects and other ophthalmological disturbances associated with vigabatrin.

Vigabatrin has been an important anticonvulsant drug for over 10 years with a reputation for high efficacy and excellent tolerability. However, since 1997, there have been over 25 reports in the literature of visual field defects attributable to the use of this agent. Most are case reports and many have only been reported as abstracts or posters or as letters or short communications. Only a small number of papers give details of patient characteristics. Typically, case reports detail ophthalmological tests such as visual acuity, funduscopic examination, integrity of colour vision, and the nature of the field cut. Many also include various electrophysiological tests which were performed in an attempt to further describe the nature of the visual changes. In order to shed light on the mechanism underlying these visual field changes, many investigators also tested various electrophysiological parameters. However, because electrophysiological testing requires considerable expertise on the part of the technician, this could be a source of variability in results and may also pose a challenge with data interpretation. The magnitude of the problem is difficult to assess. The manufacturer's estimate of incidence of visual field defects with vigabatrin was approximately 0.1%, but incidences estimated in the literature range from 6 to 30%. Since the majority of the published data are in case report form, proof of causation is also very difficult. Two papers that used proper scientific methodology to investigate this condition suggest that vigabatrin causes these changes; however, there needs to be further studies with larger populations to answer this question definitively. There is a lack of data on the dose-response characteristics of vigabatrin and the development of visual field defects. The only available data are reports of trends that implicate duration of therapy or cumulative dose. Perhaps the most important area to elucidate is whether or not the visual field defects are reversible. Data are scare on this subject, but we can hope that data will emerge as follow-up periods become more substantial. There is a need for more complete information regarding several aspects of the mechanistic basis of visual field defects associated with vigabatrin that will allow rational clinical decision making. The treatment choices, both pharmacological and nonpharmacological, for patients with refractory epilepsy have grown substantially in the last few years. Thus, it is doubtful that the clinical positioning of vigabatrin is likely to change in the future from that of a very valuable 'niche drug', with emphasis on paediatric usage.

Variability in measures of coronary lumen dimensions using quantitative coronary angiography

Objectives:The purpose of this study was to determine the true total variability of quantitative coronary angiographic measures and their components in the clinical setting.Background:Many studies describe quantitative coronary angiographic variability on the basis of repeated quantitative coronary angiographic measures from the same cineangiogram. Although these studies characterize well the performance of quantitative coronary angiographic analysis methods, they do not include other potentially important sources of variability in results of this procedure, such as day to day variations in patients and equipment or variability in selection of frames for analysis.Methods:Coronary angiograms from 20 patients who underwent diagnostic angiography followed by percutaneous transluminal coronary angioplasty an average of 2.9 days later were reviewed. A total of 30 lesions well visualized in both films were analyzed multiple times using an automated first-derivative edge-detection quantitative coronary angiographic technique.Results:The coefficient of variation for quantitative coronary angiographic measures of the same lesions from separate angiograms ranged from 8.11% to 14.01%. Average diameter was the least variable and percent diameter stenosis the most variable. Day to day variations in the patient, procedure and equipment accounted for an average of 30% of the total variability. Of the remaining variability, only 13.26% was due to variability in frame selection.Conclusions:These results provide useful information for planning clinical studies using quantitative coronary angiography, identify areas where additional improvements in this technology are needed and define more clearly the applicability of quantitative coronary angiography in the setting of routine clinical practice.

Leukocyte immunophenotyping by flow cytometry in a multisite study: Standardization, quality control, and normal values in the Transfusion Safety Study

The Transfusion Safety Study (TSS) is a multicenter, cooperative investigation of factors that may determine the occurrence and modify the expression of transusion-transmitted infections. A flow cytometry laboratory was established in each of the six participating centers in order to avoid alterations in cell phenotypes which may be caused by shipping delays, temperature changes, and handling. As a consequence, in order to assure compatibility of results, stringent standardization, quality control, and proficiency testing procedures were developed. This paper documents (i) the effect of time from phlebotomy to specimen staining and then to analysis for the antibodies used in the study; (ii) the effects of variations in light scatter cursor location for certain antibodies; (iii) a quality control program and data management and analysis system, each specifically designed for the study; and (iv) presents extensive data on age- and sex-related reference (normal) ranges for the several individual and paired monoclonal antibodies used in the study. Problems encountered, including obtaining reliable absolute lymphocyte counts, interference by nucleated erythrocytes, and sources of variability in results, are discussed. This study is meant to serve as a reference for future TSS publications.

Effects of analog and digital filtering on brain stem auditory evoked potentials

Most investigators of the brain stem auditory evoked potentials utilize analog filters to reduce the noise content of the averaged signals, but different investigators use different filter bandwidths. Data presented in this note compare the effects of different upper and lower cutoff frequencies for both analog and zero-phase shift digital filters. Effects on response wave form and on measured values of amplitude and latency of wave V are considered. It is concluded that, for given cutoff frequencies, analog filtering causes more distortion of the response than digital filtering, due primarily to phase distortion introduced by the analog filter. It is likely that differences in filter cutoff frequencies, especially lower cut-off frequencies, are a significant source of variability in results reported by different investigators.