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PubMed2001

Linkages between FAO agroclimatic data resources and the development of GIS models for control of vector-borne diseases.

The Food and Agriculture Organization (FAO) of the United Nations is the largest specialized UN Agency dealing with agriculture, forestry and fishery, particularly in the developing countries. One of its technical services, placed under the Sustainable Development Department, has the responsibility to provide information on environment and natural resources as related to food and agriculture. It includes, among others, expertise in remote sensing, geographic information systems and agrometeorology, production of global environmental digital datasets, meteorological and remote sensing data collection and analysis at near real-time, development of methodologies, models and tools for data standardization, collection, spatialization, analysis and dissemination, networking and information sharing, development of integrated information management systems. Some experience has also been gained in the use of climatic digital datasets for spatial modeling of crop pests and diseases. The description of mapping the distribution of the Western Corn rootworm (Diabrotica virgifera) in Europe as a function of environmental conditions is presented as well as the global assessment of environmental potential constraints based on processing of digital datasets. A simple spatial interpolation routine is briefly explained.

Animals↗
PubMed2003

Four-dimensional ultrasonography of the fetal heart with spatiotemporal image correlation.

OBJECTIVE: This study was undertaken to describe a new technique for the examination of the fetal heart using four-dimensional ultrasonography with spatiotemporal image correlation (STIC). STUDY DESIGN: Volume data sets of the fetal heart were acquired with a new cardiac gating technique (STIC), which uses automated transverse and longitudinal sweeps of the anterior chest wall. These volumes were obtained from 69 fetuses: 35 normal, 16 with congenital anomalies not affecting the cardiovascular system, and 18 with cardiac abnormalities. Dynamic multiplanar slicing and surface rendering of cardiac structures were performed. To illustrate the STIC technique, two representative volumes from a normal fetus were compared with volumes obtained from fetuses with the following congenital heart anomalies: atrioventricular septal defect, tricuspid stenosis, tricuspid atresia, and interrupted inferior vena cava with abnormal venous drainage. RESULTS: Volume datasets obtained with a transverse sweep were utilized to demonstrate the cardiac chambers, moderator band, interatrial and interventricular septae, atrioventricular valves, pulmonary veins, and outflow tracts. With the use of a reference dot to navigate the four-chamber view, intracardiac structures could be simultaneously studied in three orthogonal planes. The same volume dataset was used for surface rendering of the atrioventricular valves. The aortic and ductal arches were best visualized when the original plane of acquisition was sagittal. Volumes could be interactively manipulated to simultaneously visualize both outflow tracts, in addition to the aortic and ductal arches. Novel views of specific structures were generated. For example, the location and extent of a ventricular septal defect was imaged in a sagittal view of the interventricular septum. Furthermore, surface-rendered images of the atrioventricular valves were employed to distinguish between normal and pathologic conditions. Representative video clips were posted on the Journal's Web site to demonstrate the diagnostic capabilities of this new technique. CONCLUSION: Dynamic multiplanar slicing and surface rendering of the fetal heart are feasible with STIC technology. One good quality volume dataset, obtained from a transverse sweep, can be used to examine the four-chamber view and the outflow tracts. This novel method may assist in the evaluation of fetal cardiac anatomy.

Cohort Studies↗
PubMed2002

Reliability of transmembrane predictions in whole-genome data.

Transmembrane prediction methods are generally benchmarked on a set of proteins with experimentally verified topology. We have investigated if the accuracy measured on such datasets can be expected in an unbiased genomic analysis, or if there is a bias towards 'easily predictable' proteins in the benchmark datasets. As a measurement of accuracy, the concordance of the results from five different prediction methods was used (TMHMM, PHD, HMMTOP, MEMSAT, and TOPPRED). The benchmark dataset showed significantly higher levels (up to five times) of agreement between different methods than in 10 tested genomes. We have also analyzed which programs are most prone to make mispredictions by measuring the frequency of one-out-of-five disagreeing predictions.

Algorithms↗
PubMed1999

A survey of genes in Eimeria tenella merozoites by EST sequencing.

A study of about 500 expressed sequence tags (ESTs), derived from a merozoite cDNA library, was initiated as an approach to generate a larger pool of gene information on Eimeria tenella. Of the ESTs, 47.7% had matches with entries in the databases, including ribosomal proteins, metabolic enzymes and proteins with other functions, of which 14.3% represented previously known E. tenella genes. Thus over 50% of the ESTs had no significant database matches. The E. tenella EST dataset contained a range of highly abundant genes comparable with that found in the EST dataset of T. gondii and may thus reflect the importance of such molecules in the biology of the apicomplexan organisms. However, comparison of the two datasets revealed very few homologies between sequences of apical organelle molecules, and provides evidence for sequence divergence between these closely-related parasites. The data presented underpin the potential value of the EST strategy for the discovery of novel genes and may allow for a more rapid increase in the knowledge and understanding of gene expression in the merozoite life cycle stage of Eimeria spp.

Animals↗
PubMed2003

New approach based on fuzzy logic and principal component analysis for the classification of two-dimensional maps in health and disease. Application to lymphomas.

Two-dimensional (2D) electrophoresis is the most wide spread technique for the separation of proteins in biological systems. This technique produces 2D maps of high complexity, which creates difficulties in the comparison of different samples. The method proposed in this paper for the comparison of different 2D maps can be summarised in four steps: (a) digitalisation of the image; (b) fuzzyfication of the digitalised map in order to consider the variability of the two-dimensional electrophoretic separation; (c) decoding by principal component analysis of the previously obtained fuzzy maps, in order to reduce the system dimensionality; (d) classification analysis (linear discriminant analysis), in order to separate the samples contained in the dataset according to the classes present in said dataset. This method was applied to a dataset constituted by eight samples: four belonging to healthy human lymph-nodes and four deriving from non-Hodgkin lymphomas. The amount of fuzzyfication of the original map is governed by the sigma parameter. The larger the value, the more fuzzy theresulting transformed map. The effect of the fuzzyfication parameter was investigated, the optimal results being obtained for sigma = 1.75 and 2.25. Principal component analysis and linear discriminant analysis allowed the separation of the two classes of samples without any misclassification.

Electrophoresis, Gel, Two-Dimensional↗
PubMed1999

Study on genotoxic effects of the space environment: a comparison between experienced cosmonauts and unexposed Russian twins.

The molecular analysis of T-lymphocytes from experienced cosmonauts and seven pairs of unexposed twins was performed [M. Khaidakov, D. Young, H. Erfle, A. Mortimer, Y. Voronkov, B.W. Glickman, Molecular analysis of mutations in T-lymphocytes from experienced soviet cosmonauts, Environ. Mol. Mutagen, 30 (1997) 21-30; J. Curry, G. Bebb, J. Moffat, D. Young, M. Khaidakov, A. Mortimer, B.W. Glickman, Similar mutant frequencies observed between monozygotic twins, Human Mutation, 9 (1997) 445-451]. Hprt mutant frequencies (MF) in both datasets were considerably higher (38.0+/-14.6x10(-6) in cosmonauts, and 18.5+/-8.9x10(-6) in twins) than in the background Western control (8-12x10(-6)), [A.D. Tates, F.J. van Dam, H. van Mossel, H. Shoemaker, J.C.P. Thijssen, V.M. Woldring, A.H. Zwinderman, A.T. Natarajan, Use of the clonal assay for the measurement of frequencies of HPRT mutants in T-lymphocytes from five control populations, Mutation Res., 253 (1991) 199-213; R.F. Branda, L.M. Sullivan, J.P. O'Neill, M.T. Falta, J.A. Nicklas, B. Hirsch, P.M. Vacek, R.J. Albertini, Measurement of HPRT mutant frequencies in T-lymphocytes from healthy human populations, Mutation Res., 285 (1993) 267-279]. The distribution of mutations by class in the twin dataset was essentially similar to the background Western control, whereas cosmonaut samples demonstrated a significant excess of splice errors and complex mutations. The distribution of base substitutions showed similar trends in both the cosmonaut and twin samples, which are quite distinct compared to those seen in the Western control. The differences observed between cosmonaut and twin samples (a 2-fold higher MF and an excess of complex mutations in cosmonaut mutational spectra) could be an indication of possible effects of the space environment. However, these changes could also be age-related because the twin group was, on average, 17 years younger. Moreover, very similar patterns of base substitution distribution in both datasets suggest the involvement of certain region-specific factors reflected in mutational spectra. In order to discriminate between occupation and region-specific factors contributing to mutagenesis, an additional study involving trainees and cosmonauts with recent long-term flight experience is required.

Adult↗
PubMed2003

Assessment of the surface water quality in Northern Greece.

The application of different multivariate statistical approaches for the interpretation of a large and complex data matrix obtained during a monitoring program of surface waters in Northern Greece is presented in this study. The dataset consists of analytical results from a 3-yr survey conducted in the major river systems (Aliakmon, Axios, Gallikos, Loudias and Strymon) as well as streams, tributaries and ditches. Twenty-seven parameters have been monitored on 25 key sampling sites on monthly basis (total of 22,350 observations). The dataset was treated using cluster analysis (CA), principal component analysis and multiple regression analysis on principal components. CA showed four different groups of similarity between the sampling sites reflecting the different physicochemical characteristics and pollution levels of the studied water systems. Six latent factors were identified as responsible for the data structure explaining 90% of the total variance of the dataset and are conditionally named organic, nutrient, physicochemical, weathering, soil-leaching and toxic-anthropogenic factors. A multivariate receptor model was also applied for source apportionment estimating the contribution of identified sources to the concentration of the physicochemical parameters. This study presents the necessity and usefulness of multivariate statistical assessment of large and complex databases in order to get better information about the quality of surface water, the design of sampling and analytical protocols and the effective pollution control/management of the surface waters.

Environmental Monitoring↗
PubMed2002

Quantitative structure-activity relationships (QSARs) for the prediction of skin permeation of exogenous chemicals.

Quantitative structure-activity relationships (QSARs) for the skin permeability coefficients of 158 compounds through excised human skin in vitro have been developed. A number of compounds, including hydrocortisone derivatives, were removed from the dataset as reported permeability data for these compounds was considered to be in error. QSARs developed for the dataset with the outliers removed included terms for hydrophobicity, molecular size, and hydrogen bonding. These descriptors provided an excellent fit to the data (r2 = 0.90), are easily calculated from molecular structure, and are mechanistically interpretable. Further analyses of the dataset indicated that good QSARs could be developed utilising hydrophobicity and molecular size alone, with molecular volume and molecular weight providing good quantification of molecular size.

Culture Techniques↗
PubMed2006

3-month and 12-month mortality after first liver transplant in adults in Europe: predictive models for outcome.

BACKGROUND: Mortality after liver transplantation depends on heterogeneous recipient and donor factors. Our aim was to assess risk of death and to develop models to help predict mortality after liver transplantation. METHODS: We analysed data from 34,664 first adult liver transplants from the European Liver Transplant Registry to identify factors associated with mortality at 3-months (n=21,605 in training dataset) and 12-months (n=18,852 in training dataset) after transplantation. We used multivariable logistic regression models to generate mortality scores for each individual, and assessed model discrimination and calibration on an independent validation dataset (n=9489 for 3-month model and n=8313 for 12-month model). FINDINGS: 2540 of 21,605 (12%) individuals in the 3-month training sample had died by 3 months. Compared with those transplanted in 2000-03, those transplanted earlier had a higher risk of death. Increased mortality at 3-months post-transplantation was associated with acute liver failure (adjusted odds ratio 1.61), donor age older than 60 years (1.16), compatible (1.22) or incompatible (2.07) donor-recipient blood group, older recipient age (1.12 per 5 years), split or reduced graft (1.96), total ischaemia time of longer than 13 h (1.38), and low United Network for Organ Sharing score (score 1: 2.43; score 2: 1.67). However, cirrhosis with hepatocellular carcinoma, alcohol cirrhosis, hepatitis C or primary biliary cirrhosis, donor age 40 years or younger, or less, hepatitis B, and larger size of transplant centre (> or = 70 transplants per year) were associated with improved early outcomes. The 3-month mortality score discriminated well between those who did and did not die in the validation sample (C statistic=0.688). We noted similar findings for 12-month mortality, although deaths were generally underestimated at this timepoint. INTERPRETATION: The 3-month and 12-month mortality models can be effectively used to assess outcomes both within and between centres. Furthermore, the models provide a means of assessing the risk of post-transplantation mortality, giving clinicians important data on which to base strategic decisions about transplant policy in particular individuals or groups.

Adult↗
PubMed1997

Preliminary assessment of three-dimensional magnetic resonance imaging for various colonic disorders.

BACKGROUND: Improvements in magnetic resonance imaging (MRI) technology have enabled the acquisition of three-dimensional MRI datasets in a single breath hold. We adopted this technique to make a three dimensional intraluminal and extraluminal assessment of the colon in three patients with various colonic disorders. METHODS: One patient was studied after having a double-contrast barium enema. Two patients had MRI scans after colonoscopy, which showed three colonic tumours in one and multiple polyps in the ascending colon of the other. The process of rectal filling with 1.5-2.0 L water mixed with 15-20 mL 0.5 mol/L gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) was monitored with MR fluoroscopic sequence. Three-dimensional datasets of the contrast-filled colon were taken with patients in prone (before and after intravenous administration of 0.1 mmol/kg bodyweight Gd-DTPA) and supine positions. 64 sections with a voxel-resolution of 2.0 x 2.0 x 1.25 mm3-were taken during a 28 s breath hold. Three-dimensional maximum intensity projection, multiplanar reconstruction, and virtual colonoscopic images of the colon were created from these. FINDINGS: Analysis of the coronal source images in conjunction with multiplanar reconstructions revealed all relevant abnormalities, including diverticula, carcinomas, and polyps. Three dimensional maximum-intensity projections gave a morphological overview of the whole colon. Targeted projections, made up of a limited number of coronal source images, showed diverticula and smaller polyps more clearly. After patients were given intravenous contrast all colonic mass lesions were enhanced. Datasets obtained in prone patients gave the best intraluminal views of the colon. Virtual magnetic resonance colonoscopy showed colonic haustra as well as the ileocaecal valve, but did not show clearly the diverticula. All intraluminal mass lesions, on the other hand, were easy to see. INTERPRETATION: The potential of three-dimensional colonic MRI to provide accurate, minimally invasive, cost-effective polyp screening, as well as comprehensive colonic tumour staging, warrants further investigation.

Aged↗
PubMed2001

Genome analysis with gene-indexing databases.

The recent release of the draft sequence and the eventual completion of the human genome present the scientific community with a rich source of data to mine. Yet, these data are content poor in the absence of additional correlative information. Expressed sequence tag (EST) datasets and their associated gene indices have existed for many years, and represent the first attempt at understanding the complexity of the genome. These datasets remain extremely important as information sources and, in particular, as tools for analyzing the completed genomes. Here, we discuss the nature of ESTs and their associated tools and gene-indexing databases. In particular, we will compare three EST gene indices (UNIGENE, Merck Gene Index Version 2.0 and Doubletwist CAT), discuss how these gene indices are applied for both genome analysis and drug discovery, and demonstrate their importance as a complementary dataset to the annotated human genome.

Databases, Factual↗
PubMed2001

Profiling the malaria genome: a gene survey of three species of malaria parasite with comparison to other apicomplexan species.

We have undertaken the first comparative pilot gene discovery analysis of approximately 25,000 random genomic and expressed sequence tags (ESTs) from three species of Plasmodium, the infectious agent that causes malaria. A total of 5482 genome survey sequences (GSSs) and 5582 ESTs were generated from mung bean nuclease (MBN) and cDNA libraries, respectively, of the ANKA line of the rodent malaria parasite Plasmodium berghei, and 10,874 GSSs generated from MBN libraries of the Salvador I and Belem lines of Plasmodium vivax, the most geographically wide-spread human malaria pathogen. These tags, together with 2438 Plasmodium falciparum sequences present in GenBank, were used to perform first-pass assembly and transcript reconstruction, and non-redundant consensus sequence datasets created. The datasets were compared against public protein databases and more than 1000 putative new Plasmodium proteins identified based on sequence similarity. Homologs of previously characterized Plasmodium genes were also identified, increasing the number of P. vivax and P. berghei sequences in public databases at least 10-fold. Comparative studies with other species of Apicomplexa identified interesting homologs of possible therapeutic or diagnostic value. A gene prediction program, Phat, was used to predict probable open reading frames for proteins in all three datasets. Predicted and non-redundant BLAST-matched proteins were submitted to InterPro, an integrated database of protein domains, signatures and families, for functional classification. Thus a partial predicted proteome was created for each species. This first comparative analysis of Plasmodium protein coding sequences represents a valuable resource for further studies on the biology of this important pathogen.

Animals↗
PubMed2002

Bridging structural biology and genomics: assessing protein interaction data with known complexes.

Currently, there is a major effort to map protein-protein interactions on a genome-wide scale. The utility of the resulting interaction networks will depend on the reliability of the experimental methods and the coverage of the approaches. Known macromolecular complexes provide a defined and objective set of protein interactions with which to compare biochemical and genetic data for validation. Here, we show that a significant fraction of the protein-protein interactions in genome-wide datasets, as well as many of the individual interactions reported in the literature, are inconsistent with the known 3D structures of three recent complexes (RNA polymerase II, Arp2/3 and the proteasome). Furthermore, comparison among genome-wide datasets, and between them and a larger (but less well resolved) group of 174 complexes, also shows marked inconsistencies. Finally, individual interaction datasets, being inherently noisy, are best used when integrated together, and we show how simple Bayesian approaches can combine them, significantly decreasing error rate.

Actin-Related Protein 3↗
PubMed2004

Validation of two algorithms to evaluate the interface between bone and orthopaedic implants.

The level of fit and fill of the prosthetic stem in the femoral canal is an important parameter when planning a cementless total hip arthroplasty. However, the standard templates used in combination with radiographs are not always effective in the pre-operative evaluation of the level of fitting. For this reason, two algorithms were developed able to provide clinically relevant three-dimensional indicators of the implant fit and fill in the host femur, based on the CT data of each specific patient as collected in vivo. In this study the computational methods were described and validated using digital phantom datasets. Then the algorithms were applied for in vivo datasets and the sensitivity of each indicator was evaluated. The validation showed that the two algorithms are accurate from a computational point of view. Moreover, the in vivo testing demonstrated that the developed methods provide reasonable quantitative indicators of the stem positioning in the femoral CT dataset.

Algorithms↗
PubMed2005

Autonomous evolutionary algorithm in medical data analysis.

An autonomous evolutionary algorithm for constructing decision trees is presented. The algorithm requires no or minimal human interaction and shows some interesting properties when used on different medical datasets. The algorithm uses a non-standard implicit fitness evaluation in the selection phase of a co-evolving environment. Together with self-adaptation of evolution parameters and with some other improvements it can monitor and adjust its own behavior. The algorithm's capability to self-adapt to a given problem is used as a measure to predict if some dataset is just difficult or impossible to analyze. The autonomous algorithm on average produces very general solutions or gives no solution if the dataset is prone to the overfitting problem.

Algorithms↗
PubMed1999

Dose-volume analysis for quality assurance of interstitial brachytherapy for breast cancer.

PURPOSE/OBJECTIVE: The use of brachytherapy in the management of breast cancer has increased significantly over the past several years. Unfortunately, few techniques have been developed to compare dosimetric quality and target volume coverage concurrently. We present a new method of implant evaluation that incorporates computed tomography-based three-dimensional (3D) dose-volume analysis with traditional measures of brachytherapy quality. Analyses performed in this fashion will be needed to ultimately assist in determining the efficacy of breast implants. METHODS AND MATERIALS: Since March of 1993, brachytherapy has been used as the sole radiation modality after lumpectomy in selected protocol patients with early-stage breast cancer treated with breast-conserving therapy. Eight patients treated with high-dose-rate (HDR) brachytherapy who had surgical clips outlining the lumpectomy cavity and underwent computed tomography (CT) scanning after implant placement were selected for this study. For each patient, the postimplant CT dataset was transferred to a 3D treatment planning system. The lumpectomy cavity, target volume (lumpectomy cavity plus a 1-cm margin), and entire breast were outlined on each axial slice. Once all volumes were entered, the programmed HDR brachytherapy source positions and dwell times were imported into the 3D planning system. Using the tools provided by the 3D planning system, the implant dataset was then registered to the visible implant template in the CT dataset. The distribution of the implant dose was analyzed with respect to defined volumes via dose-volume histograms (DVH). Isodose surfaces, the dose homogeneity index, and dosimetric coverage of the defined volumes were calculated and contrasted. All patients received 32 Gy to the entire implanted volume in 8 fractions of 4 Gy over 4 days. RESULTS: Three-plane implants were used for 7 patients and a two-plane implant for 1 patient. The median number of needles per implant was 16.5 (range 11-18). Despite visual verification by the treating physician that surgical clips (with an appropriate margin) were within the boundaries of the implant needles, the median proportion of the lumpectomy cavity that received the prescribed dose was only 87% (range 73-98%). With respect to the target volume, a median of only 68% (range 56-81%) of this volume received 100% of the prescribed dose. On average, the minimum dose received by at least 90% of the target volume was 22 Gy (range 17.3-26.9), which corresponds to 69% of the prescribed dose. CONCLUSION: Preliminary results using our new technique to evaluate implant quality with CT-based 3D dose-volume analysis appear promising. Dosimetric quality and target volume coverage can be concurrently analyzed, allowing the possibility of evaluating implants prospectively. Considering that target volume coverage may be suboptimal even after radiographically verifying accurate implant placement, techniques similar to this need to be developed to ultimately determine the true efficacy of brachytherapy in the management of breast cancer.

Brachytherapy↗
PubMed2000

Improving the dosimetric coverage of interstitial high-dose-rate breast implants.

PURPOSE/OBJECTIVE: We performed a retrospective computed tomography (CT)-based three-dimensional (3D) dose-volume analysis of high-dose-rate (HDR) interstitial breast implants to evaluate the adequacy of lumpectomy cavity coverage, and then designed a simple, reproducible algorithm for dwell-time adjustment to correct for underdosage of the lumpectomy cavity. METHODS AND MATERIALS: Since March 1993, brachytherapy has been used as the sole radiation modality after lumpectomy in selected protocol patients with early-stage breast cancer treated with breast-conserving therapy. In this protocol, all patients received 32 Gy in 8 fractions of 4 Gy over 4 days. Eleven patients treated with HDR brachytherapy who underwent CT scanning after implant placement were included in this analysis. For each patient, the postimplant CT dataset was transferred to a 3D treatment planning system, and the relevant tissue volumes were outlined on each axial slice. The implant dataset, including the dwell positions and dwell times, were imported into the 3D planning system and then registered to the visible implant template in the CT dataset. The calculated dose distribution was analyzed with respect to defined volumes via dose-volume histograms. Due to the variability of lumpectomy cavity coverage discovered in this 3D quality assurance analysis, dwell times at selected positions were adjusted in an attempt to improve dosimetric coverage of the lumpectomy cavity. Using implant data from 5 cases, a dwell-time adjustment algorithm was designed and was then tested on 11 cases. In this algorithm, a point P was identified using axial CT images, which was representative of the underdosed region within the cavity. The distance (d) from point P to the nearest dwell position was measured. A number of dwell positions (N) nearest to point P were selected for dwell time adjustment. The algorithm was tested by increasing the dwell times of a variable number of positions (N = 1, 3, 5, 7, 10, and 20) by a weighting factor (alpha), where alpha = f(d) and alpha > 1, and subsequently performing 3D dose-volume analysis to evaluate the improvement in lumpectomy cavity coverage. RESULTS: Before adjustment in the 11 implants, the median proportion of the lumpectomy cavity and target volume that received at least the prescription dose was 85% and 68%, respectively. After dwell-time adjustment, lumpectomy cavity coverage was significantly improved in all 11 cases. The median distance from point P to the nearest dwell position (d) was 1.4 cm (range 0.9-1.9). The median volume of the lumpectomy cavity receiving 32 Gy increased from 85.3% in the actual implant to 97.0% (range 74-100%) by increasing the dwell time of a single dwell position by a median factor (alpha) of 12.2 according to the above algorithm. With N = 3, the median proportion of the cavity volume receiving 32 Gy was improved to 97.5% (range 77-100%), with a median alpha of 5.7. Further improvement in lumpectomy cavity coverage was relatively small by increasing additional dwell times. In addition, with N = 20, the median absolute volume of breast tissue receiving 150% of the prescription dose was 70.3 cm3 compared to 26.3 cm3 in the actual implant; whereas with N = 1 or N = 3, this median volume was only 35.9 and 42.0 cm3, respectively. CONCLUSION: Lumpectomy cavity coverage sometimes appears suboptimal with interstitial HDR breast brachytherapy using our current technique. A simple dwell-time increase at only 1-3 dwell positions can compensate for some underdosage without creating significant regions of overdosage. Using simple methodology, a single reference point representing the underdosed region can be utilized for initial selection of the dwell positions to be increased.

Algorithms↗
PubMed1998

Correspondence analysis as a tool in fungal taxonomy.

The polyphasic approach to taxonomic problems has led to the creation of complex datasets that lend themselves to numerical analysis. The numerical study, however, has to deal with mathematical problems linked with the presence of mixed-type data originating from the investigations. Correspondence analysis (CA) is an ordination technique widely used in ecology and social sciences but only rarely applied to taxonomic problems. In CA corresponding variables and taxa ordination are obtained simultaneously, thus allowing to explore the taxonomic interrelationships between taxa and variables in a single analysis. CA can be used on large and small datasets, and can be applied to mixed-type data after appropriate coding. It is not sensitive to variation of class number and size and is useful to screen large unstructured datasets, to suggest which variables should be retained to discriminate samples, to detect outliers or erroneous data and to perform identification of unknown samples. It also has the advantage of handling missing data particularly well. On the other hand, CA is sensitive to outliers, which can cause a distortion of the geometric map of the points in the graphical display. Nevertheless, the sensitivity of correspondence analysis to outliers can be effectively used to verify data. Finally, based on symmetry of row and column analyses correspondence analysis can be applied to find out which characters can be used to construct identification keys and to selectively group variables by their importance for the discrimination of samples.

Cluster Analysis↗