Independent Sources Of Information Research Articles

The wisdom of stalemates: consensus and clustering as filtering mechanisms for improving collective accuracy.

Groups of organisms, from bacteria to fish schools to human societies, depend on their ability to make accurate decisions in an uncertain world. Most models of collective decision-making assume that groups reach a consensus during a decision-making bout, often through simple majority rule. In many natural and sociological systems, however, groups may fail to reach consensus, resulting in stalemates. Here, we build on opinion dynamics and collective wisdom models to examine how stalemates may affect the wisdom of crowds. For simple environments, where individuals have access to independent sources of information, we find that stalemates improve collective accuracy by selectively filtering out incorrect decisions (an effect we call stalemate filtering). In complex environments, where individuals have access to both shared and independent information, this effect is even more pronounced, restoring the wisdom of crowds in regions of parameter space where large groups perform poorly when making decisions using majority rule. We identify network properties that tune the system between consensus and accuracy, providing mechanisms by which animals, or evolution, could dynamically adjust the collective decision-making process in response to the reward structure of the possible outcomes. Overall, these results highlight the adaptive potential of stalemate filtering for improving the decision-making abilities of group-living animals.

QUALIFICATION-BASED SELECTION OF CONSULTANTS AND CONTRACTORS: BREAKING THE LOWEST TENDER PRICE CULTURE

Qualification-Based Selection (QBS) is designed to focus on the abilities of consultants and contractors that will undertake an infrastructure project and, more importantly, on their past performance working with and for the client on previous projects. This paper presents a review of QBS procurement in the US and in New Zealand and details the advantages and disadvantages from the client’s perspective on major public infrastructure projects. The study involved a survey of 26 public agencies, seven case studies, and a content analysis of 81 QBS project procurement documents. The study then triangulated the three independent sources of information to draw conclusions. The paper finds that QBS awards have been used successfully in a variety of procurement methods, and clients expect to increase the likelihood of project success by decreasing the chance that a marginally qualified contractor would win a major project. Additionally, respondents received tangible benefits associated with selecting contractors that were well-qualified and had a record of satisfactory performance. The paper’s primary contribution is to demonstrate the value for money to the client when changing focus from lowest tendering cost to contractor qualifications and past performance.

Governance and Electoral Integrity: Evidence from Subnational India

This article presents the findings of perceptions of electoral integrity survey for subnational elections in India between 2015 and 2017. The perceptions of electoral integrity survey is an attempt to provide a comprehensive, impartial and independent source of information derived from experts about elections conforming to internationally recognized principles and standards. The article then evaluates the factors that account for differences in the perceptions of electoral integrity in India. We show that higher-income states in India tend to have higher levels of electoral integrity. However, we argue that differences in the quality of governance best explain subnational variation in the perceptions of electoral integrity in India.

Herpetological phylogeographic analyses support a Miocene focal point of Himalayan uplift and biological diversification.

The Himalaya are among the youngest and highest mountains in the world, but the exact timing of their uplift and origins of their biodiversity are still in debate. The Himalayan region is a relatively small area but with exceptional diversity and endemism. One common hypothesis to explain the rich montane diversity is uplift-driven diversification—that orogeny creates conditions favoring rapid in situ speciation of resident lineages. We test this hypothesis in the Himalayan region using amphibians and reptiles, two environmentally sensitive vertebrate groups. In addition, analysis of diversification of the herpetofauna provides an independent source of information to test competing geological hypotheses of Himalayan orogenesis. We conclude that the origins of the Himalayan herpetofauna date to the early Paleocene, but that diversification of most groups was concentrated in the Miocene. There was an increase in both rates and modes of diversification during the early to middle Miocene, together with regional interchange (dispersal) between the Himalaya and adjacent regions. Our analyses support a recently proposed stepwise geological model of Himalayan uplift beginning in the Paleocene, with a subsequent rapid increase of uplifting during the Miocene, finally giving rise to the intensification of the modern South Asian Monsoon.

Absorbed doses in bricks and TL-dosimeters due to anthropogenic and natural environmental radiation sources

Radiation doses accumulated in ceramic or brick and assessed by thermoluminescence (TL) or optically stimulated luminescence (OSL) measurements are commonly used as a source of independent dosimetric information, helpful for validation of retrospective estimates of population exposures to anthropogenic radiation sources. This work systematically evaluates contributions to the cumulative dose in brick samples located at different heights in a wall from anthropogenic and natural radiation sources and provides data for quantification of the natural background component of the total dose in the brick derived in TL/OSL-measurements. Al- and Cu-cased thermoluminescence dosimeters (TLD) based on Al2O3:C are used to measure contemporary doses in brick walls as benchmarks and for validation of the dose reconstruction procedures. Correspondingly, doses in TLD and in brick in the same locations and under the same irradiation conditions are obtained by Monte Carlo simulations of radiation transport in realistic geometries. The data obtained in the simulations indicate that energy response of Al-cased dosimeters agrees better with the energy response of the brick than the response of Cu-cased TLD. The dosimetric data and relationships between doses in TLD and in brick are systematically derived for different locations in the wall and above the ground and used in other dose reconstruction studies with luminescence techniques.

The relevance of ecoregions and mountainous environments in the diversity and endemism of land gastropods

Twenty-five sub-ecoregions make Argentina from southern South America a favored area to study the mutual correspondence between environments and biodiversity. Unfortunately, efforts devoted to study these environments are unbalanced, with the subtropical dry forests less studied than the tropical and subtropical humid ones. Since the limits of ecoregions are based on vegetation criteria, land gastropods represent an independent source of information to test the relevance of sub-ecoregions in different aspects of biodiversity. We ask if land gastropods mirror these traditional diversity patterns when their distributions are framed in the context of sub-ecoregions. Additionally, we want to test if short-range endemic species (SRE) are randomly scattered across the sub-ecoregions. We first built an updated taxonomic checklist and mapped all the valid records compiled to date. Taxonomic richness, taxonomic diversity, and beta-diversity between sub-ecoregions were calculated. We obtained a hierarchical grouping of sub-ecoregions and the respective list of species that significantly support each cluster. We also developed two new analytical resources: a radial plot for showing the species composition of clusters resolved at three taxonomic levels, and a mixed coefficient of distributional size useful to identify SRE from sparse point records. This dimensionless measure of spatial range combines information of both the convex hull area and the length of the minimum spanning tree connecting point localities of presence. The Southern Andean Yungas and Dry Chaco are the species-level richest ecoregions. Although the Paranaense Forest harbors half of the number of species found in the Chaco Serrano, it reaches the highest score of taxonomic diversity because of the eclectic nature of their genera. SRE species are not randomly distributed across the sub-ecoregions, but they broadly overlap with the orographic Peripampasic arc extended over Chaco Serrano and Yungas Forests. SREs are highly dependent on the physical nature of the landscape.

A Cotton Disease Diagnosis Method Using a Combined Algorithm of Case-Based Reasoning and Fuzzy Logic

Abstract In this study, a cotton disease diagnosis method that uses a combined algorithm of case-based reasoning (CBR) and fuzzy logic was designed and implemented. It focuses on the prevention, diagnosis and control of diseases affecting cotton production in China. Conventional methods of disease diagnosis are primarily based on CBR with reference to user-provided symptoms; however, in most cases, user-provided symptoms do not fully meet the requirements of CBR. To address this problem, fuzzy logic is incorporated into CBR to allow for more flexible and accurate models. With the help of CBR and fuzzy reasoning, three diagnostic results can be obtained by the cotton disease diagnosis system (CDDS) constructed in this study: success, success but not exact and failure. To verify the reliability of the CDDS and its ability to diagnose cotton diseases, its diagnostic accuracy and stability were analyzed and compared with the results obtained by the traditional expert scoring method. The analysis results reveal that the CDDS can achieve a high diagnostic success rate (above 90%) and better diagnostic stability than the traditional expert scoring method when at least four disease symptoms are input. The CDDS provides an independent and objective source of information to assist farmers in the diagnosis and prevention of cotton diseases.

Occupational risks and forecasting of working conditions

Predicting injury in any field of activity is an integral part of a broader trend: predicting working conditions. This direction is a new method and is in the process of formation. However, in comparison with the existing areas of forecasting (demographic, fundamental research, economic, etc.), there are general principles that should be used. What is common is the mathematical apparatus and the principle itself. An independent source of information for forecasting, its reliability, and places of concentration. According to most researchers, the most reliable method for predicting injuries is the mathematical method of analysis.

Identification of Single Spectral Lines through Supervised Machine Learning in a Large HST Survey (WISP): A Pilot Study for Euclid and WFIRST

Future surveys focusing on understanding the nature of dark energy (e.g., Euclid and WFIRST) will cover large fractions of the extragalactic sky in near-IR slitless spectroscopy. These surveys will detect a large number of galaxies that will have only one emission line in the covered spectral range. In order to maximize the scientific return of these missions, it is imperative that single emission lines are correctly identified. Using a supervised machine-learning approach, we classified a sample of single emission lines extracted from the WFC3 IR Spectroscopic Parallel survey (WISP), one of the closest existing analogs to future slitless surveys. Our automatic software integrates a SED fitting strategy with additional independent sources of information. We calibrated it and tested it on a "gold" sample of securely identified objects with multiple lines detected. The algorithm correctly classifies real emission lines with an accuracy of 82.6%, whereas the accuracy of the SED fitting technique alone is low (~50%) due to the limited amount of photometric data available (<=6 bands). While not specifically designed for the Euclid and WFIRST surveys, the algorithm represents an important precursor of similar algorithms to be used in these future missions.

The Role of Graffiti Game Boards in the Understanding of an Archaeological Site: The Gebel el-Silsila Quarries

Graffiti game boards attest to the presence of historical populations at an archaeological site and, in some cases, assist in dating an archaeological context. While games suggest the presence of a social activity, their contextual significance compared to the graffiti of texts and images, pottery finds, and other diagnostic tools of archaeology is open to further enquiry. The presence of multiple board game traditions at Gebel el-Silsila in Egypt creates an ideal environment to study the differences between graffiti texts and images, excavated materials and game boards when they are found in the same location. It is shown that game boards may confirm human presence in different historical time periods for which only limited additional evidence exists, or they may signal the presence of a different historical population. Their symbolic significance remains unclear, but game boards otherwise provide an independent source of information and an asset to a general archaeological inquiry.

Integrating lexical and prosodic features for automatic paragraph segmentation

Spoken documents, such as podcasts or lectures, are a growing presence in everyday life. Being able to automatically identify their discourse structure is an important step to understanding what a spoken document is about. Moreover, finer-grained units, such as paragraphs, are highly desirable for presenting and analyzing spoken content. However, little work has been done on discourse based speech segmentation below the level of broad topics. In order to examine how discourse transitions are cued in speech, we investigate automatic paragraph segmentation of TED talks using lexical and prosodic features. Experiments using Support Vector Machines, AdaBoost, and Neural Networks show that models using supra-sentential prosodic features and induced cue words perform better than those based on the type of lexical cohesion measures often used in broad topic segmentation. Moreover, combining a wide range of individually weak lexical and prosodic predictors improves performance, and modelling contextual information using recurrent neural networks outperforms other approaches by a large margin. Our best results come from using late fusion methods that integrate representations generated by separate lexical and prosodic models while allowing interactions between these features streams rather than treating them as independent information sources. Application to ASR outputs shows that adding prosodic features, particularly using late fusion, can significantly ameliorate decreases in performance due to transcription errors.

"WE SHALL TELL YOU THE TRUTH": "VOICE OF AMERICA" IN THE GLOBAL INFORMATION SPACE (1940-IES – BEGINNING OF THE XXI CENTURY)

The aim of the article is to provide a complex survey of the American broadcasting station "Voice of America’s" history since its establishment to the beginning of the XXI century. The methodology of the research is based on combination of the general and special historical methods and principles of historical cognition, namely scientificity, historicism, systematicity, objectivity. The principles of historicism, systematicity and scientificity provide for tracing the activity of "Voice of America" and its causal relationships with the historical and political background and, in particular, the foreign policy agenda of the US government. The objectivity principle is involved while highlighting the activity of the broadcasting station. Alongside with the critical analysis of the source base, it stands for defining the conceptual background of "Voice of America’s" operation, its regularities and certain aspects. The principle of systematicity makes it possible to create a holistic image of a broadcaster’s activity in 1940-ies-at the beginning of the XXI century. Taking into account the specifics of the topic, the article employs an interdisciplinary approach actualized due to categorial and scientific-research instruments of other social and humanitarian sciences, particularly politology. &#x0D; The scientific novelty of the article is attained by a pioneer attempt in the Ukrainian historiography to conduct a complex analysis of "Voice of America’s" activity throughout its history. The results obtained by the author prove that "Voice of America" has been an important constituent of the US policy in the global information space. Thereat, it is not a representative of a certain power or public group, the activity of journalists and editorial offices in forming the information content is independent and based on the principles of journalism ethics. Due to this factor, the broadcasting station has a reputation of an independent and reliable source of topical and balanced information. "Voice of America" has adapted to the qualitative transformations in the globalization epoch information space in the course of XX-XXI centuries and turned into a powerful multimedia system attracting the largest audience in the world.

Sensing the Same Fishing Fleet with AIS and VIIRS: A Seven-Year Assessment of Squid Jiggers in FAO Major Fishing Area 41

Global Fishing Watch and VIIRS-DNB (visible infrared imaging radiometer suite day/night band) signals are compared for the jigger fleet in FAO (Food and Agriculture Organization of the United Nations) Major Fishing Area 41 during the maximum feasible time span (2012–2018). Both signals have shown a high degree of consistency at all temporal and spatial scales analyzed, including seasonal cycles, lack of signal for some years and interannual tendencies. This indicates that both signals are a fair representation of the fishing effort exerted by the jigger fleet in this zone. The high degree of consistency does not support views questioning satellite AIS (automatic identification system) as a reliable tool to survey fishing activities. Instead, our results add evidence supporting the value of remote sensing, in particular, when independent sources of information (such as VIIRS-DNB and AIS) are combined, as a relevant tool to add transparency and support compliance of fishing activities in vast and distant regions of the ocean.

General knowledge as an evidential category

AbstractNumerous studies have dealt with the coding of information sources within and across languages. These studies have shown that despite the significant differences in the number of formally distinct evidentiality categories, languages tend to have grammaticalized markers for certain information sources, but not for others; different kinds of sensory perception, inference, assumption and hearsay evidence are among those information sources that receive explicit coding. In this paper, another evidence type, namely general knowledge, will be examined. It will be shown that general knowledge differs from other information sources in its nature, but it also has features in common with them. In addition, a formal-functional typology of general knowledge coding will be proposed based on the nature of the element used for this purpose. Finally, the rationale behind the discussed types and the central theoretical implications of the paper will be discussed. The attested types either stress the peculiar nature of general knowledge providing evidence for its independent information source status, or they emphasize the common features shared by general knowledge and other information sources, most notably reliability of information.

Sea Level Trends and Variability of the Baltic Sea From 2D Statistical Reconstruction and Altimetry

2D sea level trend and variability fields of the Baltic Sea were reconstructed based on statistical modeling of monthly tide gauge observations, and model reanalysis as a reference. The reconstruction included both absolute and relative sea level in 11 km resolution over the period 1900-2014. The reconstructed monthly sea level had an average correlation of 96% and root mean square error of 3.8 cm with 56 tide gauges which are independent of the statistical model. The statistical reconstruction of sea level was based on multiple linear regression and took land deformation information into account. An assessment of the quality of an open ocean altimetry product (ESA Sea Level CCI ECV, hereafter “the CCI”) in this regional sea was performed by validating the variability against the reconstruction as an independent source of sea level information. The validation allowed determining how close to the coast the CCI can be considered reliable. The CCI matched reconstructed sea level variability with correlation above 90% and RMS difference below 6 cm in the southern and open part of the Baltic Proper. However, areas with seasonal sea ice and areas of high natural variability need special treatment. The reconstructed relative sea level change, which is important for coastal communities, was dominated by isostatic land movements. This pattern was confirmed by independent observations and the values were provided along the entire coastline of the Baltic Sea. The area averaged absolute sea level rise for the Baltic Sea was 1.3 ± 0.3 mm/yr for the 20th century, which was slightly below the global mean for the same period. Considering the relative shortness of the satellite era, natural variability made trend estimation sensitive to the selected data period, but the linear trends derived from the reconstruction (3.4 ± 0.7 mm/yr for 1993-2014) fitted with those of the CCI (4.0 ± 1.4 mm/yr for 1993-2015) and with global mean estimates within the limits of uncertainty.

Prediction and interpretation of miRNA-disease associations based on miRNA target genes using canonical correlation analysis

BackgroundIt has been shown that the deregulation of miRNAs is associated with the development and progression of many human diseases. To reduce time and cost of biological experiments, a number of algorithms have been proposed for predicting miRNA-disease associations. However, the existing methods rarely investigated the cause-and-effect mechanism behind these associations, which hindered further biomedical follow-ups.ResultsIn this study, we presented a CCA-based model in which the possible molecular causes of miRNA-disease associations were comprehensively revealed by extracting correlated sets of genes and diseases based on the co-occurrence of miRNAs in target gene profiles and disease profiles. Our method directly suggested the underlying genes involved, which could be used for experimental tests and confirmation. The inference of associated diseases of a new miRNA was made by taking into account the weight vectors of the extracted sets.We extracted 60 pairs of correlated sets from 404 miRNAs with two profiles for 2796 target genes and 362 diseases. The extracted diseases could be considered as possible outcomes of miRNAs regulating the target genes which appeared in the same set, some of which were supported by independent source of information. Furthermore, we tested our method on the 404 miRNAs under the condition of 5-fold cross validations and received an AUC value of 0.84606. Finally, we extensively inferred miRNA-disease associations for 100 new miRNAs and some interesting prediction results were validated by established databases.ConclusionsThe encouraging results demonstrated that our method could provide a biologically relevant prediction and interpretation of associations between miRNAs and diseases, which were of great usefulness when guiding biological experiments for scientific research.

Performance-based outcomes following patellar tendon repair in professional athletes

ABSTRACTObjectives: There are limited data on the impact of a patellar tendon repair to a professional athlete’s career. The purpose of this study was to determine differences return to play (RTP) rate, career length, and performance-based outcomes after a patellar tendon repair in professional athletes of four different sports.Methods: Participants met inclusion criteria if initial reports of the date and type of surgery were corroborated by at least two independent sources of information through a well-established protocol of public newspaper archives, team injury reports, and player profiles. Players with other concomitant injuries of the knee or treated nonoperatively were excluded. One hundred and three athletes across professional baseball, basketball, American football, and soccer athletes were identified and met inclusion criteria. RTP rate, career length, and sports-specific performance statistics (i.e. player efficiency rating (PER) for professional basketball players) before and after surgery were collected for each athlete.Results: Seventy-nine (76.7%) professional athletes successfully RTP. American football athletes had the lowest RTP rate and the largest drop in performance in post-operative season 1 (P < 0.001). These athletes also experienced the shortest adjusted career lengths (P = 0.003) compared to players in the other sports. Basketball athletes played significantly less games through post-operative seasons 1 to 3 (P < 0.05). Soccer athletes had less goals and assists per game and played fewer games (P < 0.05) in post-operative season 1 that recovered to baseline by seasons 2 and 3.Conclusion: A patellar tendon rupture is a potentially devastating injury for the professional athlete. American football players appeared to have the worst postoperative outcome with the lowest RTP rate and a most significant decrease in performance in the first postoperative season. This procedure also had a significant short-term impact on soccer athletes who sustained decreases in short-term game performance. These findings are likely explained by the unique physical demands imposed by each sport.

Modelling and Mapping Elusive Locations of Historic Water-Powered Grist Mills

Abstract. Grist mills are structures in which stone wheels are used to grind grain (e.g. corn, wheat) into a powder-like form for human consumption. Circular stone wheels provided the pressure to grind the grain and separate seed components. In most grist mills the energy for turning the heavy stones was derived from water power. The most visible part of some these mills was the externally mounted water wheel. However, other common configurations of the water ‘turbine’ internal to the structure were used (Figure 1). While grist mills existed in Europe at least as early as the 11th century such mills were not present in the United States until the last 1600s. No comprehensive census has been conducted for grist mills in the U.S. although an estimate of all water powered mills in eastern U.S. was 65,000 in 1840. Many of these water powered mills in the census estimate were for textile, sawmills, manufacturing, and other non-grain-grinding applications.Most often, the mill site included a small impoundment for creating a reliable source of water during low-flow stream conditions. These ponds were created in the late 1700s and especially in the 1800s as a reliable water source for turning grist or saw mills. By the middle of the 20th century the grist mills had all but vanished. Except for a few historic relics and conversion to touristic sites, the mill infrastructure has disappeared on the landscape while the mill ponds typically remain, serving other purposes, such as fishing or hunting lakes, or merely aesthetic environments.The local ecosystems around the mills sites have been artificially modified by the presence of these stream impoundments providing a new environment for fish, mammals, avian species, and of course, humans. While numerous positive ecosystem values may be observed from their continued presence, the risk of dam failure to both downstream systems and humans is substantial. In fact, such a catastrophic series of dam failures (51 in South Carolina) occurred in October of 2015 from a heavy rainfall event. In other instances the impoundments now store toxic sediment originating from sources farther upstream such as mining, military or industrial processes.Where are these historic mill sites and mill ponds? No inventory of mills or their ponds exist in South Carolina (and only for a few northeastern states). In this research we developed a systematic approach for identifying and mapping historic mill sites and ponds using a geohistorical framework and applied to South Carolina. The approach relied on 1) numerous geospatial sources, and 2) an analytical model of confidence mapping for predicting sites. The developed approach resulted in a new database of definitive and likely historic mill sites and mill pond locations throughout South Carolina. The sources of geospatial information was largely cartographic in nature including the following:USGS Historic Topographic Map SeriesRobert Mills 1820 atlas covering South CarolinaHistoric aerial photographyNational Hydrography Data (NHD)National Wetlands Inventory (NWI)National Inventory of DamsSC Department of Health and Environmental Control for Regulated DamsToponyms from the Geographic Names Information System (GNIS)U.S. Census TIGER street dataThe design for a predictive model (Figure 2) using diverse historic data with various scales and reliability is problematic. Most of the grist mills have disappeared from the landscape and do not exist in contemporary geospatial databases. Historic maps might include toponyms for the sites or ponds but their map projection, scale, and subsequent distortions in geometry are problematic. In addition, some of the sources for data are derived from a similar source and thus, are not statistically independent. The design of the analytical model for mapping confidence in mill site locations was calibrated and subsequently validated using several independent sources of information. Numerous field visits to known and suspected locations for mills sites were conducted throughout the physiographic regions of South Carolina.The model of likelihood included factors for the reliability of the source, the mapping scale and spatial accuracy of the source, correlation with other sources, and likelihood of correspondence with grist mills.

Methods and algorithms for creation of structural schemes of rivers

Methods and algorithms for creation of structural schemes of rivers

Automated macrophage counting in DLBCL tissue samples: a ROF filter based approach

BackgroundFor analysis of the tumor microenvironment in diffuse large B-cell lymphoma (DLBCL) tissue samples, it is desirable to obtain information about counts and distribution of different macrophage subtypes. Until now, macrophage counts are mostly inferred from gene expression analysis of whole tissue sections, providing only indirect information. Direct analysis of immunohistochemically (IHC) fluorescence stained tissue samples is confronted with several difficulties, e.g. high variability of shape and size of target macrophages and strongly inhomogeneous intensity of staining. Consequently, application of commercial software is largely restricted to very rough analysis modes, and most macrophage counts are still obtained by manual counting in microarrays or high power fields, thus failing to represent the heterogeneity of tumor microenvironment adequately.MethodsWe describe a Rudin-Osher-Fatemi (ROF) filter based segmentation approach for whole tissue samples, combining floating intensity thresholding and rule-based feature detection. Method is validated against manual counts and compared with two commercial software kits (Tissue Studio 64, Definiens AG, and Halo, Indica Labs) and a straightforward machine-learning approach in a set of 50 test images. Further, the novel method and both commercial packages are applied to a set of 44 whole tissue sections. Outputs are compared with gene expression data available for the same tissue samples. Finally, the ROF based method is applied to 44 expert-specified tumor subregions for testing selection and subsampling strategies.ResultsAmong all tested methods, the novel approach is best correlated with manual count (0.9297). Automated detection of evaluation subregions proved to be fully reliable. Comparison with gene expression data obtained for the same tissue samples reveals only moderate to low correlation levels. Subsampling within tumor subregions is possible with results almost identical to full sampling. Mean macrophage size in tumor subregions is 152.5±111.3 μm2.ConclusionsROF based approach is successfully applied to detection of IHC stained macrophages in DLBCL tissue samples. The method competes well with existing commercial software kits. In difference to them, it is fully automated, externally repeatable, independent on training data and completely documented. Comparison with gene expression data indicates that image morphometry constitutes an independent source of information about antibody-polarized macrophage occurence and distribution.