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At least 1,009 records · Page 56Linked to original sources
PubMed2005

Risk-based approach to appraise valve closure in the clam Corbicula fluminea in response to waterborne metals.

We developed a risk-based approach to assess how the valve closure behavior of Asiatic clam Corbicula fluminea responds to waterborne copper (Cu) and cadmium (Cd). We reanalyzed the valve closure response data from published literature to reconstruct the response time-dependent dose-response profiles based on an empirical three-parameter Hill equation model. We integrated probabilistic exposure profiles of measured environmental Cu and Cd concentrations in the western coastal areas of Taiwan with the reconstructed dose-response relationships at different integration times of response to quantitatively estimate the valve response risk. The risk assessment results implicate exposure to waterborne Cu and Cd may pose no significant risk to clam valve activity in the short-time response periods (e.g., <30 min), yet a relative high risk for valve closure response to waterborne Cu at response times greater than 120 min is alarming. We successfully linked reconstructed dose-response profiles and EC50-time relationships associated with the fitted daily valve opening/closing rhythm characterized by a three-parameter lognormal function to predict the time-varying bivalve closure rhythm response to waterborne metals. We parameterized the proposed predictive model that should encourage a risk-management framework for discussion of future design of biological monitoring systems.

Animals↗
PubMed2004

Radial arrangement of chromosome territories in human cell nuclei: a computer model approach based on gene density indicates a probabilistic global positioning code.

Numerous investigations in the last years focused on chromosome arrangements in interphase nuclei. Recent experiments concerning the radial positioning of chromosomes in the nuclear volume of human and primate lymphocyte cells suggest a relationship between the gene density of a chromosome territory (CT) and its distance to the nuclear center. To relate chromosome positioning and gene density in a quantitative way, computer simulations of whole human cell nuclear genomes of normal karyotype were performed on the basis of the spherical 1 Mbp chromatin domain model and the latest data about sequence length and gene density of chromosomes. Three different basic assumptions about the initial distribution of chromosomes were used: a statistical, a deterministic, and a probabilistic initial distribution. After a simulated decondensation in early G1, a comparison of the radial distributions of simulated and experimentally obtained data for CTs Nos. 12, 18, 19, and 20 was made. It was shown that the experimentally observed distributions can be fitted better assuming an initial probabilistic distribution. This supports the concept of a probabilistic global gene positioning code depending on CT sequence length and gene density.

Biophysics↗
PubMed2002

NasoNet, modeling the spread of nasopharyngeal cancer with networks of probabilistic events in discrete time.

The spread of cancer is a non-deterministic dynamic process. As a consequence, the design of an assistant system for the diagnosis and prognosis of the extent of a cancer should be based on a representation method that deals with both uncertainty and time. The ultimate goal is to know the stage of development of a cancer in a patient before selecting the appropriate treatment. A network of probabilistic events in discrete time (NPEDT) is a type of Bayesian network for temporal reasoning that models the causal mechanisms associated with the time evolution of a process. This paper describes NasoNet, a system that applies NPEDTs to the diagnosis and prognosis of nasopharyngeal cancer. We have made use of temporal noisy gates to model the dynamic causal interactions that take place in the domain. The methodology we describe is general enough to be applied to any other type of cancer.

Artificial Intelligence↗
PubMed2004

Cost-benefit analysis of first-generation antihistamines in the treatment of allergic rhinitis.

BACKGROUND: The majority of individuals with allergic rhinitis in the US take first-generation antihistamines (FGAs). Although FGAs have been proven effective in alleviating allergic rhinitis symptoms, they have been associated with an increased risk of motor vehicle, aviation and occupational injuries and deaths, reduced productivity and impaired learning. OBJECTIVE: The objective of this analysis was to quantify the total costs and benefits of FGA use in the US from the societal perspective. METHODS: We used a decision-analytic model to quantify the annual societal costs and benefits of treatment with FGAs compared with the hypothetical alternative of no treatment for the population of individuals with allergic rhinitis and taking FGAs in the US in 2001. The benefit associated with FGA use was estimated using the willingness-to-pay framework and projected to the US population using published estimates of the prevalence of allergic rhinitis. The costs of FGA-associated sedation included lost productivity and the direct and indirect cost of unintentional injuries (including motor vehicle, occupational, public and home injuries and fatalities). The incidence of injuries and fatalities associated with FGA use was estimated using the risk of injury attributable to the sedentary effects of FGAs in the allergic rhinitis population. To evaluate uncertainty in the model assumptions, a probabilistic sensitivity analysis was conducted using Bayesian second-order Monte Carlo simulation. Costs and benefits are expressed in 2001 US dollars, using a 3% discount rate. RESULTS: Based on current utilisation, the total societal benefit (95% credible interval) associated with the use of FGAs for the treatment of allergic rhinitis was US 7.7 billion dollars (US 1.3 billion dollars to US 21 billion dollars). The societal cost of purchasing FGAs was only US 697 million dollars. However, the societal cost of FGA-associated sedation was US 11.3 billion dollars (US 2.4 billion dollars to US 50.8 billion dollars). The annual societal net benefit of FGA use for the treatment of allergic rhinitis in the US was -US4.2 billion dollars (-US 36 billion dollars to +US 0.296 billion dollars). The net benefit was negative in 97% of the 10,000 Monte Carlo simulations. CONCLUSIONS: The societal benefits of FGA use in alleviating the symptoms of allergic rhinitis are significant. However, based on the assumptions, probability distributions and parameter estimate ranges used in the current model, it is very likely that the costs associated with sedation exceed the benefits of FGA use in the US. The cost of FGA-associated sedation is comparable to estimates of the cost of all medical care expenditures on respiratory conditions in the US (US 12.1 billion dollars to US 31.3 billion dollars) [1996 values] and provides compelling evidence of the economic burden of sedation associated with FGA use.

Accidents↗
PubMed2004

Enhancement of information transmission efficiency by synaptic failures.

Many synapses have a high percentage of synaptic transmission failures. I consider the hypothesis that synaptic failures can increase the efficiency of information transmission across the synapse. I use the information transmitted per vesicle release about the presynaptic spike train as a measure of synaptic transmission efficiency and show that this measure can increase with the synaptic failure probability. I analytically calculate the Shannon mutual information transmitted across two model synapses with probabilistic transmission: one with a constant probability of vesicle release and one with vesicle release probabilities governed by the dynamics of synaptic depression. For inputs generated by a non-Poisson process with positive autocorrelations, both synapses can transmit more information per vesicle release than a synapse with perfect transmission, although the information increases are greater for the depressing synapse than for a constant-probability synapse with the same average transmission probability. The enhanced performance of the depressing synapse over the constant-release-probability synapse primarily reflects a decrease in noise entropy rather than an increase in the total transmission entropy. This indicates a limitation of analysis methods, such as decorrelation, that consider only the total response entropy. My results suggest that synaptic transmission failures governed by appropriately tuned synaptic dynamics can increase the information-carrying efficiency of a synapse.

Models, Neurological↗
PubMed2003

Economic evaluation of oral valdecoxib versus diclofenac in the treatment of patients with rheumatoid arthritis in a randomized clinical trial.

In contrast to economic models that provide probabilistic estimates of economic impact, data extracted from clinical trials may be used to evaluate and compare actual resource utilization and costs. Health-care resource utilization and the costs of these resources were compared from the perspective of the UK National Health Service using data obtained in a 6-month clinical trial of oral valdecoxib 20 mg once daily and diclofenac 75 mg twice daily for the symptomatic treatment of rheumatoid arthritis. However, calculated health-care costs were exclusive of drug acquisition costs because the price of valdecoxib was not available at the time of analysis. While the efficacy of the two treatments was similar, use of valdecoxib was associated with a reduction in total health-care costs amounting to approximately 200 British pounds per patient. This lower cost was associated with reduced use of health-care resources for gastrointestinal serious adverse events (gastrointestinal SAEs). In particular, the incidence of hospitalization and number of hospital days for gastrointestinal SAEs was lower in the valdecoxib group. Analysis of cost per gastrointestinal SAE favoured valdecoxib (cost savings of 742 British pounds), suggesting that even when these events did occur they were less severe. When costs of gastrointestinal SAEs were averaged over the entire population, valdecoxib was suggested to have lower total costs per patient compared with diclofenac (cost savings of 115 British pounds per patient), mainly resulting from significant savings in hospitalization costs (76.49 British pounds per patient). These data are consistent with economic models and suggest that the favourable gastrointestinal profile of valdecoxib observed in clinical trials will be of economic benefit.

Administration, Oral↗
PubMed2005

Mining genetic epidemiology data with Bayesian networks I: Bayesian networks and example application (plasma apoE levels).

MOTIVATION: The wealth of single nucleotide polymorphism (SNP) data within candidate genes and anticipated across the genome poses enormous analytical problems for studies of genotype-to-phenotype relationships, and modern data mining methods may be particularly well suited to meet the swelling challenges. In this paper, we introduce the method of Belief (Bayesian) networks to the domain of genotype-to-phenotype analyses and provide an example application. RESULTS: A Belief network is a graphical model of a probabilistic nature that represents a joint multivariate probability distribution and reflects conditional independences between variables. Given the data, optimal network topology can be estimated with the assistance of heuristic search algorithms and scoring criteria. Statistical significance of edge strengths can be evaluated using Bayesian methods and bootstrapping. As an example application, the method of Belief networks was applied to 20 SNPs in the apolipoprotein (apo) E gene and plasma apoE levels in a sample of 702 individuals from Jackson, MS. Plasma apoE level was the primary target variable. These analyses indicate that the edge between SNP 4075, coding for the well-known epsilon2 allele, and plasma apoE level was strong. Belief networks can effectively describe complex uncertain processes and can both learn from data and incorporate prior knowledge. AVAILABILITY: Various alternative and supplemental networks (not given in the text) as well as source code extensions, are available from the authors. SUPPLEMENTARY INFORMATION: http://bioinformatics.oxfordjournals.org.

Apolipoproteins E↗
PubMedDate not supplied

Gene expression profiling and breast cancer care: what are the potential benefits and policy implications?

PURPOSE: Gene expression profiling has been proposed as an alternative to clinical guidelines to identify high-risk patients for adjuvant chemotherapy. However, the outcomes associated with gene expression profiling are not clear, and guidelines for the appropriate use of genomic technologies have not been established. METHODS: We developed a decision analytic model to evaluate the incremental cost and quality-adjusted life years of gene expression profiling versus NIH clinical guidelines in a hypothetical cohort of premenopausal early stage breast cancer patients 44 years of age. We conducted empirical analyses and identified literature-based data to inform the model, and performed probabilistic sensitivity analyses to evaluate uncertainty in the results. We interpreted the implications of our findings for treatment guidelines and policies. RESULTS: Use of gene expression profiling resulted in an absolute 5% decrease in the proportion of cases of distant recurrence prevented, 0.21 fewer quality-adjusted life years, and a cost savings of USD 2882. The chosen test cutoff value to identify a tumor as poor prognosis and the cost of adjuvant chemotherapy were the most influential parameters in the analysis, but our findings did not change substantially in sensitivity analyses. Regardless of the test cutoff used to identify a poor prognosis tumor, the gene expression profiling assay studied in our analysis, at its current level of performance, did not attain the threshold sensitivity (95%) necessary to produce equal or greater quality-adjusted life years than NIH guidelines. CONCLUSION: Although the use of gene expression profiling in breast cancer care holds great promise, our analysis suggests additional refinement and validation are needed before use in clinical practice.

Adult↗
PubMed1999

Cost-effectiveness of malaria control in sub-Saharan Africa.

BACKGROUND: Information on the cost-effectiveness of malaria control is needed for the WHO Roll Back Malaria campaign, but is sparse. We used mathematical models to calculate cost-effectiveness ratios for the main prevention and treatment interventions in sub-Saharan Africa. METHODS: We analysed interventions to prevent malaria in childhood (insecticide-treated nets, residual spraying of houses, and chemoprophylaxis) and pregnancy (chloroquine chemoprophylaxis and sulfadoxine-pyrimethamine intermittent treatment), and to improve malaria treatment (improved compliance, improved availability of second-line and third-line drugs, and changes in first-line drug). We developed models that included probabilistic sensitivity analysis to calculate ranges for the cost per disability-adjusted life year (DALY) averted for each intervention in three economic strata. Data were obtained from published and unpublished sources, and consultations with researchers and programme managers. FINDINGS: In a very-low-income country, for insecticide treatment of existing nets, the cost-effectiveness range was US$4-10 per DALY averted; for provision of nets and insecticide treatment $19-85; for residual spraying (two rounds per year) $32-58; for chemoprophylaxis for children $3-12 (assuming an existing delivery system); for intermittent treatment of pregnant women $4-29; and for improvement in case management $1-8. Although some interventions are inexpensive, achieving high coverage with an intervention to prevent childhood malaria would use a high proportion of current health-care expenditure. INTERPRETATION: Cost-effective interventions are available. A package of interventions to decrease the bulk of the malaria burden is not, however, affordable in very-low-income countries. Coverage of the most vulnerable groups in Africa will require substantial assistance from external donors.

Adolescent↗
PubMed2005

Three surveillance strategies for vancomycin-resistant enterococci in hospitalized patients: detection of colonization efficiency and a cost-effectiveness model.

OBJECTIVE: To evaluate the cost-effectiveness and detection sensitivity associated with three active surveillance strategies for the identification of patients harboring vancomycin-resistant enterococci (VRE) to determine which is the most medically and economically useful. DESIGN: Culture for VRE from 200 consecutive stool specimens submitted for Clostridium difficile culture. Following this, risk factors were assessed for patients whose culture yielded VRE, and a cost-effectiveness evaluation was performed using a decision analytic model with a probabilistic analysis. SETTING: A 688-bed, tertiary-care facility in Chicago, Illinois, with approximately 39,000 annual admissions, 7,000 newborn deliveries, 56,000 emergency department visits, and 115,000 home care and 265,000 outpatient visits. SUBJECTS: All stool specimens submitted to the clinical microbiology laboratory for C. difficile culture from hospital inpatients. RESULTS: From 200 stool samples submitted for C. difficile testing, we identified 5 patients with VRE in non-high-risk areas not screened as part of our routine patient surveillance. Medical record review revealed that all 5 had been hospitalized within the prior 2 years. Three of 5 had a history of renal impairment. The strategy that would involve screening the greatest number of patients (all those with a history of hospital admission in the prior 2 years) resulted in highest screening cost per patient admitted (dollars 2.48), lower per patient admission costs (dollars 480), and the best survival rates. CONCLUSION: An expanded VRE surveillance program that encompassed all patients hospitalized within the prior 2 years was a cost-effective screening strategy compared with a more traditional one focused on high-risk units.

Carrier State↗
PubMed1997

Computational methods for probabilistic decision trees.

Decision tree models may be more realistic if branching probabilities (and possibly utilities) are represented as distributions rather than point estimates. However, numerical analysis of such "probabilistic" trees is more difficult. This study employed the Mathematica computer algebra system to implement and verify previously described probabilistic methods. Both algebraic approximations and Monte Carlo simulation methods were used; in particular, simulations with beta, logistic-normal, and triangular distributions for branching probabilities were compared. Algebraic and simulation methods of sensitivity analysis were also implemented and compared. Computation required minimal programming and was reasonably fast using Mathematica on a standard personal computer. This study verified previously published results, including methods of sensitivity analysis. Changing the input distributional form had little effect. Computation is no longer a significant barrier to the use of probabilistic methods for analysis of decision trees.

Computer Simulation↗
PubMed2000

Modeling the toxicity of chemicals to Tetrahymena pyriformis using molecular fragment descriptors and probabilistic neural networks.

The results of an investigation into the use of a probabilistic neural network (PNN)-based methodology to model the 48-h ICG50 (inhibitory concentration for population growth) sublethal toxicity of 825 chemicals to the ciliate Tetrahymena pyriformis are presented. The information fed into the neural networks is solely based on simple molecular descriptors as can be derived from the chemical structure. In contrast to most other toxicological models, the octanol/water partition coefficient is not used as an input parameter, and no rules of thumb or other substance selection criteria are employed. The cross-validation and external validation experiments confirmed excellent recognitive and predictive capabilities of the resulting models and recommend their future use in evaluating the potential of most organic molecules to be toxic to Tetrahymena.

Animals↗
PubMed2006

Measurement of the clinical and cost-effectiveness of non-invasive diagnostic testing strategies for deep vein thrombosis.

OBJECTIVES: To estimate the diagnostic accuracy of non-invasive tests for proximal deep vein thrombosis (DVT) and isolated calf DVT, in patients with clinically suspected DVT or high-risk asymptomatic patients, and identify factors associated with variation in diagnostic performance. Also to identify practical diagnostic algorithms for DVT, and estimate the diagnostic accuracy, clinical effectiveness and cost-effectiveness of each. DATA SOURCES: Electronic databases (to April 2004). A postal survey of hospitals in the UK. REVIEW METHODS: Selected studies were assessed against validated criteria. A postal survey of hospitals in the UK was undertaken to describe current practice and availability of tests, and identify additional diagnostic algorithms. Pooled estimates of sensitivity, specificity and likelihood ratios were obtained for each test using random effects meta-analysis. The effect of study-level covariates was explored using random effects metaregression. A decision-analytic model was used to combine estimates from the meta-analysis and estimate the diagnostic performance of each algorithm in a theoretical population of outpatients with suspected DVT. The net benefit of using each algorithm was estimated from a health service perspective, using cost--utility analysis, assuming thresholds of willingness to pay of pound 20,000 and pound 30,000 per quality-adjusted life-year (QALY). The model was analysed probabilistically and cost-effectiveness acceptability curves were generated to reflect uncertainty in estimated cost-effectiveness. RESULTS: Individual clinical features are of limited diagnostic value, with most likelihood ratios being close to 1. Wells clinical probability score stratifies proximal, but not distal, DVT into high-, intermediate- and low-risk categories. Unstructured clinical assessment by experienced clinicians may have similar performance to Wells score. In patients with clinically suspected DVT, D-dimer has 91% sensitivity and 55% specificity for DVT, although performance varies substantially between assays and populations. D-dimer specificity is dependent on pretest clinical probability, being higher in patients with a low clinical probability of DVT. Plethysmography and rheography techniques have modest sensitivity for proximal DVT, poor sensitivity for distal DVT, and modest specificity. Ultrasound has 94% sensitivity for proximal DVT, 64% sensitivity for distal DVT and 94% specificity. Computed tomography scanning has 95% sensitivity for all DVT (proximal and distal combined) and 97% specificity. Magnetic resonance imaging has 92% sensitivity for all DVT and 95% specificity. The diagnostic performance of all tests is worse in asymptomatic patients. The most cost-effective algorithm discharged patients with a low Wells score and negative D-dimer without further testing, and then used plethysmography alongside ultrasound, with venography in selected cases, to diagnose the remaining patients. However, the cost-effectiveness of this algorithm was dependent on assumptions of test independence being met and the ability to provide plethysmography at relatively low cost. Availability of plethysmography and venography is currently limited at most UK hospitals, so implementation would involve considerable reorganisation of services. Two algorithms were identified that offered high net benefit and would be feasible in most hospitals without substantial reorganisation of services. Both involved using a combination of Wells score, D-dimer and above-knee ultrasound. For thresholds of willingness to pay of pound 10,000 or pound 20,000 per QALY the optimal strategy involved discharging patients with a low or intermediate Wells score and negative D-dimer, ultrasound for those with a high score or positive D-dimer, and repeat scanning for those with positive D-dimer and a high Wells score, but negative initial scan. For thresholds of pound 30,000 or more a similar strategy, but involving repeat ultrasound for all those with a negative initial scan, was optimal. CONCLUSIONS: Diagnostic algorithms based on a combination of Wells score, D-dimer and ultrasound (with repeat if negative) are feasible at most UK hospitals and are among the most cost-effective. Use of repeat scanning depends on the threshold for willingness to pay for health gain. Further diagnostic testing for patients with a low Wells score and negative D-dimer is unlikely to represent a cost-effective use of resources. Recommendations for research include the evaluation of the costs and outcomes of using the optimal diagnostic algorithms in routine practice, the development and evaluation of algorithms appropriate for specific groups of patients with suspected DVT, such as intravenous drug abusers, pregnant patients and those with previous DVT, the evaluation of the role of plethysmography: interaction with other diagnostic tests, outcome of low-risk patients with negative plethysmography and measurement of the costs of providing plethysmography, and methodological research into the incorporation of meta-analytic data into decision-analytic modelling.

Adult↗
PubMed2005

Calculations of dietary exposure to acrylamide.

In this paper we calculated the usual and acute exposure to acrylamide (AA) in the Dutch population and young children (1-6 years). For this AA levels of different food groups were used as collected by the Institute for Reference Materials and Measurements (IRMM) of the European Commission's Directorate General Joint Research Centre (JRC) from April 2003 up to May 2004. This database contained about 3500 AA levels received from mainly Germany, The Netherlands, Ireland, Greece, Austria, UK and from food industry. Food consumption levels used were derived from the Dutch National Food Consumption Survey of 1997/1998 (n=6250 of which 530 children aged 1-6 years). The exposure was estimated using the probabilistic approach. The results of the exposure calculations are discussed in relation to different methodological aspects of AA exposure calculations and possible uncertainties related to this. The items discussed include quality of the AA levels measured in food items, the allocation of AA levels to food categories, the quality of food consumption levels, and relevant exposure model in relation to reported toxicity of AA. Furthermore, we demonstrate that scenario studies and probabilistic modelling of exposure are potential useful tools to evaluate the effect of processing techniques to reduce AA levels in food on AA exposure. The scenarios studied reduced total AA exposure ranging from <1% up to 17%.

Acrylamide↗
PubMed2006

A Bayesian approach to analysing the cost-effectiveness of two primary care interventions aimed at improving attendance for breast screening.

AIMS: To assess the cost-effectiveness of two primary care interventions, a letter and a flag, aimed at improving attendance for breast screening among (i) all women invited for breast screening and (ii) non-attenders. METHODS: A probabilistic decision analytic model was developed using Markov chain Monte Carlo simulation implemented in WinBUGS. The model was populated using economic and effectiveness data collected alongside two randomised controlled trials. RESULTS: For all women invited, the incremental cost-effectiveness ratio (ICER) for the letter compared with no intervention is 27 pounds per additional attendance, and the ICER for the combined letter and flag intervention compared to the letter alone is 171 pounds. The corresponding ICERs for non-attenders are 41 pounds and 90 pounds. The flag intervention is an inefficient option in both settings. A large proportion of the costs fall on the practices (25-67%), depending on the intervention and target population. The total costs incurred do not, however, seem prohibitive. Expected value of perfect information suggests that there is greater value in carrying out further research on the intervention implemented among all women invited for breast screening rather than on non-attenders. CONCLUSIONS: The flag intervention alone does not appear to be an efficient option. The choice between the letter and both interventions combined is subjective, depending on the willingness to pay for an additional screening attendance.

Bayes Theorem↗
PubMed1995

Migration theories and behavioural models.

"This review presents a probabilistic formulation of the decision making process, leading to a rigorous treatment of migration behaviour for projection purposes....Aggregate-level models may be applied to migration flows for which the objectively measured characteristics of areas of department and destination act as subjectively measured characteristics and stimuli....Individual-level models use event history methods of analysis to introduce a great variety of characteristics of the subject on the decision to move. They lead to projections using microsimulation models. A further step is taken in integrating macro- and microbehavioural models. The use of aggregate and individual characteristics simultaneously leads to more efficient and sophisticated projection models: the factors affecting behaviour at the micro-level cannot be inferred from aggregate studies and conversely."

Behavior↗
PubMed2006

Effects of knee simulator loading and alignment variability on predicted implant mechanics: a probabilistic study.

Inherent variability in total knee arthroplasty loading and alignment, present in vivo and in simulator testing, may ultimately influence polyethylene tibial insert wear and long-term performance. The effect of this variability was quantified on implant kinematics and contact mechanics during simulated gait loading conditions using semi-constrained and unconstrained fixed bearing, cruciate retaining implants. A probabilistic finite element model of the Stanmore knee wear simulator was utilized to estimate the envelope of anterior-posterior (AP) and internal-external (IE) position and contact pressure and to evaluate the variability in corresponding ranges of motion (ROM). Variability levels were represented by standard deviations of up to 10% of the maximum value for load inputs and 0.25 mm and 0.5 degrees for component alignment inputs. Model predictions compared well with experimental simulator results for the semi-constrained implant, with predicted positional envelopes of up to 1.8 mm (AP) an 3.4 degrees (IE) for the semi-constrained and up to 2.6 mm (AP) and 3.7 degrees (IE) for the unconstrained implant at the variability levels evaluated. ROM varied by up to 22%, while peak contact pressure variations averaged less than 2 MPa for both designs. For each implant, loading variability was more influential during the swing phase of gait, while alignment variability affected kinematics more during stance. The relative rank of sensitivities showed differences between the two designs, providing insight into critical parameters affecting kinematics and contact characteristics.

Arthroplasty, Replacement, Knee↗
PubMed1999

Local frequency dependence and global coexistence.

In sessile organisms such as plants, interactions occur locally so that important ecological aspects like frequency dependence are manifest within local neighborhoods. Using probabilistic cellular automata models, we investigated how local frequency-dependent competition influenced whether two species could coexist. Individuals of the two species were randomly placed on a grid and allowed to interact according to local frequency-dependent rules. For four different frequency-dependent scenarios, the results indicated that over a broad parameter range the two species could coexist. Comparisons between explicit spatial simulations and the mean-field approximation indicate that coexistence occurs over a broader region in the explicit spatial simulation.

Ecosystem↗