Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “data reproducibility”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56Linked to original sources
PubMedDate not supplied

Comparison between a time-domain and a frequency-domain system for optical tomography.

The quality of phase and amplitude data from two medical optical tomography systems were compared. The two systems are a 32-channel time-domain system developed at University College London (UCL) and a 16-channel frequency-domain system developed at Helsinki University of Technology (HUT). Difference data measured from an inhomogeneous and a homogeneous phantom were compared with a finite-element method (diffusion equation) and images of scattering and absorption were reconstructed based on it. The measurements were performed at measurement times between 1 and 30 s per source. The mean rms errors in the data measured by the HUT system were 3.4% for amplitude and 0.51 deg for phase, while the corresponding values for the UCL data were 6.0% and 0.46 deg, respectively. The reproducibility of the data measured with the two systems was tested with a measurement time of 5 s per source. It was 0.4% in amplitude for the HUT system and 4% for the UCL system, and 0.08 deg in phase for both systems. The image quality of the reconstructions from the data measured with the two systems were compared with several quantitative criteria. In general a higher contrast was observed in the images calculated from the HUT data.

Algorithms↗
PubMed1994

[Arterial blood pressure measurement with oscillometric instruments in newborns and infants].

Non-invasive blood pressure measurements by the auscultatory method do not provide reliable, reproducible blood pressure values in many neonates because the Korottkoff sounds are often very difficult to detect. This resulted in the development of many alternative indirect methods. Devices utilizing the Doppler ultrasound technique have not found wide acceptance. Since the introduction of automated oscillometric blood pressure monitors, arterial blood pressure has been increasingly brought into discussion as an indicator of the circulatory state. This is the first study to investigate the similarity and reproducibility of the data obtained with five oscillometric devices for measurement of blood pressure in neonates. MATERIALS AND METHODS. Since investigations on the technical performance are not practical in the clinical setting of a neonatal or pediatric ward, we used two simulators, the CuffLink (Dynatech, Nevada, USA) and a device developed by the PTB (Physikalisch-Technische Bundesanstalt). While the latter uses oscillations originally obtained from neonates, the CuffLink uses artificial and therefore ideal signals for the blood pressure monitors. The signals used for the PTB simulator were obtained from three neonates with an average age of 2 months and a weight of 3.5 kg, 4.4 kg, and 7.8 kg. The following blood pressure monitors were studied: Hoyer/Colin, BP-1001; Datex, Cardiocap II; SpaceLabs, model no. 90426; Hewlett-Packard, NBP M1008A; Critikon, Dinamap 1846. Before the measurements were started, the cuff pressure display of each monitor was checked according to a verification procedure. Although the 4 mmHg margin of error was not exceeded, the results were corrected. RESULTS. The results of the measurements show significant differences between the blood pressure monitors from the various manufacturers, with the differences for the ideal signals of the CuffLink-Simulator being less pronounced than those for the PTB simulator. Direct comparison of results is therefore often impossible. The standard deviation, taken from 20 measurements per monitor and simulation, is below 4 mmHg for both simulators. We can therefore conclude that the reproducibility of data is satisfactory and the emerging trend is reliable. DISCUSSION. The difference between the results of the PTB simulator and the CuffLink are probably due to the method of evaluation and the identification of artifacts of each blood pressure monitor. This is also confirmed by the studies of Mieke et al. The manufacturers should provide devices that display comparative results and improve the algorithms for detection of artefacts, increasing the accuracy of their blood pressure monitors. This could be done with the help of simulators. Considering the pathophysiological characteristics of neonates and infants, the systematic differences between the five monitors have to be regarded as serious.

Blood Pressure Monitors↗
PubMed1995

Methodological issues in assessing reproducibility--a comparative study of various indices of reproducibility applied to repeat ELISA serologic tests for Lyme disease.

This study applies and evaluates a variety of different measures of reproducibility. As an example, repeat enzyme-linked immunosorbent assays (ELISA) for antibodies to Borrelia burgdorferi, the etiologic agent of Lyme disease, are used. These repeat tests were part of the 1991 Quality Control Assessment of provincial laboratories that was carried out by the Laboratory Centre for Disease Control (Ottawa). Twenty-seven sera from cases and non-cases were tested by three laboratories, and two laboratories repeated the tests once. Methodological issues discussed include: different methods of assessing reproducibility in the continuous scale; whether reproducibility should be assessed with data in continuous or categorical form; problems assessing the reproducibility of data that has been standardized using a calibration-regression line; and problems with external generalizability of reproducibility studies of rare diseases. The authors conclude that the statistical method used to assess the reproducibility of a test must be adjusted to suit individual study designs and data, and the usage of the test.

Antibodies, Bacterial↗
PubMed1991

Reproducibility of diurnal variation of heart rate.

Heart rate variation has been utilized as a parameter for validating autonomic nerve and sinus node function. However, few reports are available on the reproducibility of such data. In the present study, we studied the reproducibility of the diurnal variation of heart rate in 15 patients, and the effect of age differences on the variation in 30 normal men using a Holter ECG monitoring method. For investigating reproducibility, Holter ECG monitoring was performed twice, the two measurements being separated by a short interval. A moving average method applied on heart rate of every 3h exhibited essentially the same diurnal pattern of heart rate between two records in each patient. Excellent reproducibility of the pattern was also demonstrated by a lag correlation analysis. Variability of heart rate in normal men was independent of age. These results suggest that heart rate variation was essentially constant in each subject, at least within a short period.

Adult↗
PubMed1992

Selective functional depletion of HIV gp120 peptides complexed with MHC from antigen-presenting cells engaged with specific T lymphocytes.

Human T cell lines specific for different peptides of HIV envelope glycoprotein gp120 have been used as probes to identify the availability of functional MHC-peptide complexes on APC. MHC-peptide complexes recognized by T cells specific for peptide 24 (amino acids 225-240) are no longer available on the surface of APC after interaction with irradiated (binding nonproliferating) T cells with the same fine specificity. On the contrary, MHC-peptide complexes recognized by T cells specific for peptide 30 (amino acids 285-300) were functionally available and could stimulate T cells with such a specificity. The reciprocal experiment yielded similar results. The same data were also reproduced with another pair of gp120 peptides. These data demonstrate that upon clustering of peptide-specific T cells with presenting cells presentation of the same peptide to a second cohort of T cells with identical specificity is abolished, suggesting that a selective functional depletion of the MHC-peptide complexes engaged with specific T cells occurs at the surface of the presenting cells. The depletion does not affect other MHC molecules complexed with unrelated peptides.

Amino Acid Sequence↗
PubMed2002

A stochastic flowering model describing an asynchronically flowering set of trees.

A general stochastic model is presented that simulates the time course of flowering of individual trees and populations, integrating the synchronization of flowering both between and within trees. Making some hypotheses, a simplified expression of the model, called the 'shoot' model, is proposed, in which the synchronization of flowering both between and within trees is characterized by specific parameters. Two derived models, the 'tree' model and the 'population' model, are presented. They neglect the asynchrony of flowering, respectively, within trees, and between and within trees. Models were fitted and tested using data on flowering of Psidium cattleianum observed at study sites at elevations of 200, 520 and 890 m in Reunion Island. The 'shoot' model fitted the data best and reproduced the strong irregularities in flowering shown by empirical data. The asynchrony of flowering in P. cattleianum was more pronounced within than between trees. Simulations showed that various flowering patterns can be reproduced by the 'shoot' model. The use of different levels of organization of the general model is discussed.

Computer Simulation↗
PubMed2002

Expression profiling with oligonucleotide arrays: technologies and applications for neurobiology.

DNA microarrays have been used in applications ranging from the assignment of gene function to analytical uses in prognostics. However, the detection sensitivity, cross hybridization, and reproducibility of these arrays can affect experimental design and data interpretation. Moreover, several technologies are available for fabrication of oligonucleotide microarrays. We review these technologies and performance attributes and, with data sets generated from human brain RNA, present statistical tools and methods to analyze data quality and to mine and visualize the data. Our data show high reproducibility and should allow an investigator to discern biological and regional variability from differential expression. Although we have used brain RNA as a model system to illustrate some of these points, the oligonucleotide arrays and methods employed in this study can be used with cell lines, tissue sections, blood, and other fluids. To further demonstrate this point, we provide data generated from total RNA sample sizes of 200 ng.

Brain↗
PubMed1977

Methods for evaluating hermetic closures for screw-capped bottles.

With the described method, a large number of sealed bottles can be tested to determine their effectiveness, integrity, and reliability in preserving an inert atmosphere. The method consists of placing milligram quantities of dry ice into the bottles, capping them, and periodically weighing them on an analytical balance; leaky bottles are detected by a loss in weight. This method can be applied to test a large number of bottles with a minimum of effort and manpower and without complicated instrumentation. The data presented are highly reproducible and correlate well with data from other methods and with the physical defects of the bottles.

Carbon Dioxide↗
PubMed2001

Application of the Australian river bioassessment system (AUSRIVAS) in the Brantas River, East Java, Indonesia.

Assessment of river 'health' using biological methods, particularly those based on macro-invertebrates, is now commonplace in most developed countries. However, this is not the case in most developing countries, where physical and chemical methods are used to assess water quality, with very little use of biological assessment methods. This paper reports on a project that aimed to assess the possible introduction of biological assessment of river condition using the Australian River Assessment System (AUSRIVAS) into Indonesia. The paper addresses three components of the project: (1) science--does the bioassessment method work in this tropical region? (2) resources--are they adequate and if not what additional resources are needed? (3) politics--what needs to be done to convince the agencies (both central and provincial) to take up such a new philosophy and approach? A pilot study was run in the upper Brantas River, East Java. A total of 66 reference sites and 15 test sites were sampled and the macro-invertebrates collected were identified to family level. A rigorous quality-control protocol was introduced to ensure the data were reliable and reproducible. The macro-invertebrate data were used to develop a predictive model of the AUSRIVAS type for the upper Brantas River, and the model was then used to assess the 'health' of sites that were presumed to be damaged in this section of the river. A number of difficulties were experienced during the study, including: locating reference sites sufficiently unmodified by humans; lack of skills to identify animals collected; and a paucity of facilities required for aquatic macro-invertebrate identification (e.g. identification keys and good quality binocular microscopes). For resources, the major constraint to the introduction of a bioassessment capability in Indonesia is the lack of personnel trained in the bioassessment techniques. An 'on-the-job' training approach was adopted, largely because of the specialist nature of this work. Six Indonesians were trained and will now become the 'trainers' of further Indonesian scientists (we have called this process 'training-the-trainers'). For politics, it was hoped that the AUSRIVAS method would be suitable for introduction into the Indonesian national Clean River Program. A strategy was developed and implemented to ensure the method and its outputs were accepted technically by the Indonesian scientific community, and also by the resource managers and relevant government officials. Experience shows that if the latter do not see how the bioassessment information will be used for management purposes they will not accept the method even if it is scientifically sound.

Animals↗
PubMed2003

Dynamic contact angle and spreading rate measurements for the characterization of the effect of dentin surface treatments.

A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other.

Acid Etching, Dental↗
PubMed1988

Practice-based research: opportunities and obstacles.

Renewed interest in practice-based research reflects growing realization of the limitations of research from a hospital perspective. Practice-based pediatric research promises to broaden the range and severity of conditions commonly studied, to enhance the study of the natural history of disease and of normal development, to provide normal controls and standards, and to facilitate recruitment of adequate sample sizes. Cohort, incidence, and health services research will be promoted by the development of patients registries. The Chicago area Pediatric Practice Research Group is a research consortium of 81 practitioners in 27 office practices. Formed in 1984, it receives logistic and financial support from Children's Memorial Hospital, with which it is affiliated. The Pediatric Practice Research Group has undertaken six studies, most with outside funding. During these studies, some unifying characteristics of practice-based research have emerged. These include the need to tailor study protocols to individual practice characteristics and routines and the critical role of office staff in the conduct of research. Features can be identified that make specific studies more or less intrusive into office functioning. It has proved feasible to obtain data of high quality and reproducibility despite geographically scattered data collection sites. This review of Pediatric Practice Research Group activities and experience is intended to open an exchange of ideas with others interested in practice-based research.

Humans↗
PubMedDate not supplied

A noninvasive electromagnetic flowmeter.

The reliability and reproducibility of peripheral blood flow data obtained by a noninvasive electromagnetic flowmeter were tested using seven male and three female volunteers aged 15-46 years. Each subject was studied under multiple testing conditions in which time, subject's metabolic state, and electrode placement were varied. Each condition was repeated within 1 to 8 weeks to obtain test-retest data. Intraclass reliability coefficients of 0.864-0.998 were obtained on all pulsatile components both within a given measurement sessions and from one day to the next. The size and shape of the waveforms obtained from the data did not significantly differ from one another, thus indicating excellent reproducibility. No significant differences were found between data obtained from the right leg and that obtained from the left. The noninvasive electromagnetic flowmeter was found capable of providing reliable and reproducible data. For data analysis, the second of two consecutive curves seems to be the best choice for clinical assessment.

Adolescent↗
PubMed2000

The accuracy of joint surface models constructed from data obtained with an electromagnetic tracking device.

Electromagnetic tracking devices are widely used in biomechanics. In this article a method is evaluated to construct models of articular surfaces using an electromagnetic tracking device. First, the accuracy of the space tracker was examined and optimised. Then, from several joint surfaces random points were measured and eighth degree polynomials were fitted to these measurements. To check if the fit converged well, plots of cross sections of the model with corresponding data points were examined. The accuracy of the models was determined by comparing them with computed tomography data and by reproducibility tests. All the fits converged well to the data. The root mean square (RMS) error of the models varied from 0.07 to 0. 18mm, and was proportional to the size and complexity of the surface. This was mainly due to systematic errors made by the space tracker, which were also proportional to the size and complexity of the surface.

Biomechanical Phenomena↗
PubMed2004

Assessment of the reproducibility of postprocessing dynamic CT perfusion data.

BACKGROUND AND PURPOSE: Commercially available software programs for the conversion of dynamic CT perfusion (CTP) source data into cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) maps require operators to subjectively define parameters that are used in subsequent postprocessing calculations. Our purpose was to define the variability of CBV, CBF, and MTT values derived from CTP maps generated from the same source data postprocessed by three different CT technologists (CTTs). METHODS: Raw data derived from dynamic CTP examinations performed in 20 subjects were postprocessed seven times by three experienced CTTs. Parenchymal regions of interest derived from each map (CBV, CBF, and MTT) were compared. The CBF maps generated by each technologist were also qualitatively assessed. Decisions made by each analyzer during postprocessing were assessed. RESULTS: The intraclass correlation coefficients were 0.73 (95% CI, 0.64-0.81), 0.87 (0.83-0.91) and 0.89 (0.85-0.93), for the CBV, CBF, and MTT parenchymal regions of interest, respectively. All individual correlation coefficients between data sets were significant to a P value <.05. Measurement error, made solely on the basis of different technologists postprocessing the same source data and expressed as the coefficients of variation, were 31%, 30%, and 14% for CBV, CBF, and MTT, respectively. The selection of the arterial input function (AIF) region of interest, venous function region of interest, and preenhancement interval were very reproducible. The technologists differed significantly with respect to the selection of the postenhancement image (PoEI) (P <.01). A retrospective review of the individual CBF maps indicated that variance in the PoEI selection accounted for much of the variation in the qualitative appearance of the CBF maps generated by different technologists. The PoEI was selected to demarcate the baseline of the AIF time-attenuation curve. It is likely that this method of PoEI selection significantly contributed to intra- and interanalyzer variability. CONCLUSION: There is a high degree of correlation between parenchymal regions of interest derived from CBV, CBF, and MTT maps generated from the same dynamic CTP source data postprocessed by different operators. The level of agreement, however, may not be sufficient to incorporate quantitative values into clinical decision making. Quantitative differences between parenchymal regions of interest were not infrequently manifest as significant differences in the qualitative appearance of the CBF maps. It is likely that, with optimization of postprocessing parameter selection, the degree of variability may be substantially reduced.

Arizona↗
PubMed1996

Anthropometric measurements and ejection injuries.

BACKGROUND: A previous study examined anthropometric variables to determine possible ejection seat risk factors. It concluded that individuals who weighed below the average body weight or who met the criteria of having a tall, thin physique as measured by body mass index (BMI = kg.m-2) were significantly more at risk for acceleration induced back injuries. HYPOTHESIS: Because of the increased number of female pilots and the potential need to modify ejection seats for lighter aviators, this retrospective analysis of Naval Safety Center data attempted to reproduce and confirm the same results with more current data, covering a 5-yr period from Jan 1989-Dec 1993. METHODS: In this study, the same criteria were used to define back injury, including thoracic or lumbar vertebral fractures and soft tissue injuries, and the same anthropometric variables were used, including weight, height, BMI, and below average weight. Additional categories of injury were examined, including all spinal fractures alone without soft tissue back injuries, all injuries combined, and severity of injury. Sitting height and trunk height were added to the variables. RESULTS: Out of 810 aircrew involved in mishaps, 199 ejected. Of all the ejections, 111 (56%) had some type of injury as a result of the ejection. Severe injuries occurred in 8 (4%) including 4 (2%) fatalities. Back injuries occurred in 44 (22%), and 8 (4%) involved spinal fractures. Although there were no significant risk factors for ejection back injury, weight and height were statistically significant risk factors for severe injury and spinal fracture, respectively. CONCLUSIONS: Aircrew with severe injury were heavier (average weight 88 kg. vs. 79 kg.). In addition, taller aircrew (185 vs. 180 cm.) were at increased risk for any spinal fracture.

Acceleration↗
PubMedDate not supplied

A simple method of producing depth ionization data for electron energy constancy check.

A simple method has been developed to reproduce depth ionization data of electron beams for energy determination. The method utilizes a simple set of equipment, a combination of a specially designed wedge-shaped polystyrene phantom and a linear array of detectors, to collect the necessary data. The wedge-shaped phantom provides varying depths to various detectors in the array. The ionization readings received from the detectors were corrected for off-axis ratio and plotted against corresponding ray-line depths to produce depth ionization curves. The instrument setup was fast and simple. The relevant data, for a high-energy linear accelerator with multiple electron energies, were collected in minutes. The depths of 80% and 50% ionization determined by this method were found to differ by 2 and 3 mm, respectively, at the most, with those determined by a conventional method.

Biophysical Phenomena↗
PubMed2003

Lack of reproducibility of linkage results in serially measured blood pressure data.

BACKGROUND: Using the longitudinal Framingham Heart Study data on blood pressure, we analyzed the reproducibility of linkage measures from serial cross-sectional surveys of a defined population by performing genome-wide model-free linkage analyses to systolic blood pressure (SBP) and history of hypertension (HTN) measured at five separate time points. RESULTS: The heritability of SBP was relatively stable over time, ranging from 11.6 to 23.5% (coefficient of variation = 25.7%). However, the variability in linkage results was much greater. The average correlation in LOD scores at any pair of time points was 0.46 for HTN (NPL All LOD) and 0.17 for SBP (Variance Components LOD). No evidence of reproducible linkage results was found, with a mean kappa of 0.02 for linkage to HTN and -0.03 for SBP linkage. At loci with potential evidence for linkage (LOD > 1.0 at one or more time points), the correlation was even lower. The coefficient of variation at loci with potential evidence of linkage was 126% for HTN and 135% for SBP. None of 15 chromosomal regions for HTN and only one of 28 regions for SBP with potential evidence for linkage had a LOD > 1.0 at more than two of the five time points. CONCLUSION: These data suggest that, although heritability estimates at different time points are relatively robust, the reproducibility of linkage results in serial cross-sectional samples of a geographically defined population at successive time points is poor. This may explain in part the difficulty encountered in replicating linkage studies of complex phenotypes.

Adult↗
PubMed2000

Critical appraisal of the design and reporting of studies of imaging and measurement of carotid stenosis.

BACKGROUND AND PURPOSE: Several hundred studies have been published over the last few years on imaging and measurement of carotid stenosis. Despite all this research, there is still no consensus about how best to image and measure stenosis. One possible explanation for this is that many of the studies have not been large enough or methodologically sound enough to allow useful conclusions to be drawn. We aimed to assess the design and methods of a random sample of published studies of imaging and measurement of carotid stenosis using 9 simple criteria. METHODS: A formal literature search was performed for studies of imaging and measurement of carotid stenosis. Two subsets were randomly selected for detailed assessment: 20 studies published before 1991 and 20 published between 1993 and 1997 (some years after the initial publication of the ECST and NASCET trials). The criteria used to assess the selected studies were as follows: prospective rather than retrospective study design; patient selection based on a consecutive series or a random sample; adequate detail of study population; adequate detail of imaging techniques; inclusion of all investigations, ie, patients with poor-quality imaging were not excluded; blinded assessment of images; adequate detail of derivation of measurement of stenosis from images or data; adequate data on the reproducibility of measurements of stenosis; and study powered according to a sample-size calculation. RESULTS: There were many basic methodological deficiencies in both subsets of studies, with relatively little evidence of improvement with time. For example, only 33% of studies were prospective, only 45% studied a consecutive or random selection of patients, and only 38% reported any data on the reproducibility of measurements. More than half of the studies satisfied < or =4 of the 9 quality criteria. However, there was considerable variation between studies, with 7 studies satisfying > or = 7 criteria and 10 studies satisfying < or =2. No study was based on a sample-size calculation. The number of patients studied was often small, particularly in the more recent studies: median sample size was 100 in the 1970-1990 studies and 58 in the 1993-1997 studies (P<0.0001). CONCLUSIONS: The design and reporting of published studies of imaging and measurement of carotid stenosis are poor and have not improved much in recent years. The majority of published studies are not of a sufficient standard to enable the results to be used to inform clinical practice. The utility of future studies could be improved considerably by better adherence to 9 simple methodological guidelines.

Carotid Stenosis↗