Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Probability”

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

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

At least 19 recordsLinked to original sources
PubMed2004

The relationship between species detection probability and local extinction probability.

In community-level ecological studies, generally not all species present in sampled areas are detected. Many authors have proposed the use of estimation methods that allow detection probabilities that are <1 and that are heterogeneous among species. These methods can also be used to estimate community-dynamic parameters such as species local extinction probability and turnover rates (Nichols et al. Ecol Appl 8:1213-1225; Conserv Biol 12:1390-1398). Here, we present an ad hoc approach to estimating community-level vital rates in the presence of joint heterogeneity of detection probabilities and vital rates. The method consists of partitioning the number of species into two groups using the detection frequencies and then estimating vital rates (e.g., local extinction probabilities) for each group. Estimators from each group are combined in a weighted estimator of vital rates that accounts for the effect of heterogeneity. Using data from the North American Breeding Bird Survey, we computed such estimates and tested the hypothesis that detection probabilities and local extinction probabilities were negatively related. Our analyses support the hypothesis that species detection probability covaries negatively with local probability of extinction and turnover rates. A simulation study was conducted to assess the performance of vital parameter estimators as well as other estimators relevant to questions about heterogeneity, such as coefficient of variation of detection probabilities and proportion of species in each group. Both the weighted estimator suggested in this paper and the original unweighted estimator for local extinction probability performed fairly well and provided no basis for preferring one to the other.

Animals↗
PubMed1989

Probability learning and Piagetian probability conceptions in children 5 to 12 years old.

This study focused on the relations between performance on a three-choice probability-learning task and conceptions of probability as outlined by Piaget concerning mixture, normal distribution, random selection, odds estimation, and permutations. The probability-learning task and four Piagetian tasks were administered randomly to 100 male and 100 female, middle SES, average IQ children in three age groups (5 to 6, 8 to 9, and 11 to 12 years old) from different schools. Half the children were from Middle Eastern backgrounds, and half were from European or American backgrounds. As predicted, developmental level of probability thinking was related to performance on the probability-learning task. The more advanced the child's probability thinking, the higher his or her level of maximization and hypothesis formulation and testing and the lower his or her level of systematically patterned responses. The results suggest that the probability-learning and Piagetian tasks assess similar cognitive skills and that performance on the probability-learning task reflects a variety of probability concepts.

Child↗
PubMed1997

Adding a visual linear scale probability to the PIOPED probability of pulmonary embolism.

PURPOSE: Reporting a lung scintigraphy diagnosis as a PIOPED categorical probability of pulmonary embolism offers the clinician a wide range of interpretation. Therefore the purpose of this study was to analyze the impact on lung scintigraphy reporting of adding a visual linear scale (VLS) probability assessment to the ordinary PIOPED categorical probability. MATERIAL AND METHODS: The study material was a re-evaluation of lung scintigrams from a prospective study of 170 patients. All patients had been examined by lung scintigraphy and pulmonary angiography. The scintigrams were re-evaluated by 3 raters, and the probability of pulmonary embolism was estimated by the PIOPED categorization and by a VLS probability. The test was repeated after 6 months. RESULTS: There was no significant difference (p > 0.05) in the area under the ROC curve between the PIOPED categorization and the VLS for any of the 3 raters. Analysis of agreement among raters and for repeatability demonstrated low agreement in the mid-range of probabilities. CONCLUSION: A VLS probability estimate did not significantly improve the overall accuracy of the diagnosis compared to the categorical PIOPED probability assessment alone. From the data of our present study we cannot recommend the addition of a VLS score to the PIOPED categorization.

Angiography↗
PubMedDate not supplied

Qualitative probability versus quantitative probability in clinical diagnosis: a study using a computer simulation.

The use of Bayes' theorem as a diagnostic tool in clinical medicine normally requires an input of exact probability estimates. However, humans tend to think in categories ("likely," "unlikely," etc.) rather than in terms of exact probability. A computer simulation of the presenting features of a case of pelvic infection has been used to compare the effects of quantitative and qualitative probability estimates on the diagnostic accuracy of Bayes' theorem. For the commoner conditions (prior probability greater than or equal to 0.2) the use of a two- or three-category system is virtually equivalent to the use of exact probability. However, uncommon conditions (prior probability less than or equal to 0.03) are completely ignored by the qualitative system. It is concluded that the use of simple categories of probability is acceptable for a Bayesian diagnostic system provided that the target conditions have a relatively high prior probability.

Artificial Intelligence↗
PubMed1994

Risks and probabilities of breast cancer: short-term versus lifetime probabilities.

OBJECTIVE: To calculate age-specific short-term and lifetime probabilities of breast cancer among a cohort of Canadian women. DESIGN: Double decrement life table. SETTING: Alberta. SUBJECTS: Women with first invasive breast cancers registered with the Alberta Cancer Registry between 1985 and 1987. MAIN OUTCOME MEASURES: Lifetime probability of breast cancer from birth and for women at various ages; short-term (up to 10 years) probability of breast cancer for women at various ages. RESULTS: The lifetime probability of breast cancer is 10.17% at birth and peaks at 10.34% at age 25 years, after which it decreases owing to a decline in the number of years over which breast cancer risk will be experienced. However, the probability of manifesting breast cancer in the next year increases steadily from the age of 30 onward, reaching 0.36% at 85 years. The probability of manifesting the disease within the next 10 years peaks at 2.97% at age 70 and decreases thereafter, again owing to declining probabilities of surviving the interval. CONCLUSIONS: Given that the incidence of breast cancer among Albertan women during the study period was similar to the national average, we conclude that currently more than 1 in 10 women in Canada can expect to have breast cancer at some point during their life. However, risk varies considerably over a woman's lifetime, with most risk concentrated after age 49. On the basis of the shorter-term age-specific risks that we present, the clinician can put breast cancer risk into perspective for younger women and heighten awareness among women aged 50 years or more.

Adolescent↗
PubMed2005

Interpersonal comparison of subjective probabilities: toward translating linguistic probabilities.

Interpersonal variability in understanding linguistic probabilities can adversely affect decision making. Using the fact that everyone judges canonical probability events similarly in a manner consistent with axiom systems that yield a probability measure, we developed and tested a method for comparing the meanings of probability phrases across individuals. An experiment demonstrated that despite extreme heterogeneity in participants' linguistic probability lexicons, interpersonal similarity in phrase meaning is well predicted by phrase rank order within the lexicons. Thus, equally ranked phrases have similar meanings, and individual differences in linguistic probabilities may simply be explained by the phrases people use at each rank.

Decision Making↗
PubMed2001

Using full probability models to compute probabilities of actual interest to decision makers.

The objective of this paper is to illustrate the advantages of the Bayesian approach in quantifying, presenting, and reporting scientific evidence and in assisting decision making. Three basic components in the Bayesian framework are the prior distribution, likelihood function, and posterior distribution. The prior distribution describes analysts' belief a priori, the likelihood function captures how data modify the prior knowledge; and the posterior distribution synthesizes both prior and likelihood information. The Bayesian approach treats the parameters of interest as random variables, uses the entire posterior distribution to quantify the evidence, and reports evidence in a "probabilistic" manner. Two clinical examples are used to demonstrate the value of the Bayesian approach to decision makers. Using either an uninformative or a skeptical prior distribution, these examples show that the Bayesian methods allow calculations of probabilities that are usually of more interest to decision makers, e.g., the probability that treatment A is similar to treatment B, the probability that treatment A is at least 5% better than treatment B, and the probability that treatment A is not within the "similarity region" of treatment B, etc. In addition, the Bayesian approach can deal with multiple endpoints more easily than the classic approach. For example, if decision makers wish to examine mortality and cost jointly, the Bayesian method can report the probability that a treatment achieves at least 2% mortality reduction and less than $20,000 increase in costs. In conclusion, probabilities computed from the Bayesian approach provide more relevant information to decision makers and are easier to interpret.

Arterial Occlusive Diseases↗
PubMedDate not supplied

Improved estimation of the ranking probabilities in partial orders using random linear extensions by approximation of the mutual ranking probability.

The application of partial order theory and Hasse diagram technique in environmental science is getting increasing attention. One of the latest developments in the field of Hasse diagram technique is the use of random linear extensions to estimate ranking probabilities. In the original algorithm for estimating the ranking probability it is assumed that the order between two incomparable pair of objects can be chosen randomly. However, if the total set of linear extensions is considered there is a specific probability that one object will be larger than another, which can be far from 50%. In this study it is investigated if an approximation of the mutual ranking probability can improve the algorithm. Applying an approximation of the mutual ranking probability the estimation of the ranking probabilities are significantly improved. Using a test set of 39 partial orders with randomly chosen values the relative mean root square difference (MRSD) decrease in average from 7.9% to 2.2% and a maximum relative improvement of 90% can be found. In the most successful case the relative MRSD goes as low as 0.77%.

Journal Article↗
PubMed2004

You say "probable" and I say "likely": improving interpersonal communication with verbal probability phrases.

When forecasters and decision makers describe uncertain events using verbal probability terms, there is a risk of miscommunication because people use different probability phrases and interpret them in different ways. In an effort to facilitate the communication process, the authors investigated various ways of converting the forecasters' verbal probabilities to the decision maker's terms. The authors present 3 studies in which participants judged the probabilities of distinct events using both numerical and verbal probabilities. They define several indexes of interindividual coassignment of phrases to the same events and evaluate the conversion methods by comparing the values of these indexes for the converted and the unconverted judgments. In all the cases studied, the conversion methods significantly reduced the error rates in communicating uncertainties.

Adolescent↗
PubMed1972

Probability learning as a function of momentary reinforcement probability.

Pigeons were trained on a probability learning task where the overall reinforcement probability was 0.50 for each response alternative but where the momentary reinforcement probability differed and depended upon the outcome of the preceding trial. In all cases, the maximum reinforcement occurred with a "win-stay, lose-shift" response pattern. When both position and color were relevant cues, the optimal response pattern was learned when the reinforcement probability for repeating the just-reinforced response was 0.80 but not when the probability was 0.65. When only color was relevant, learning occurred much more slowly, and only for subjects trained on large fixed ratio requirements.

Journal Article↗
PubMed1991

[Diagnosis of paternity by deduction of the probable genotype of the deceased person from the relatives--in addition to the examination of the Essen-Möller value and diagnosis of paternity based on the probability distribution of log (Y/X)].

1) The present paper deals with the general formulas of paternity probability, applicable to any cases where the putative man and/or the plaintive mother are deceased, using the blood types of various relatives. Two typical examples are described. 2) Bayes's theorem is applied to the calculation of probability of paternity using the Essen-Möller's formula, in which a putative father is to be compared with any one of the men in the general population whose blood types are unidentified. Statistically, those men are supposed to have any one of several blood types, depending on the frequency of occurrence of those types. This means that their blood types include the blood type of the putative father. According to Bayes's theorem, however, probability calculations are valid only when the two types to be compared are mutually exclusive. Consequently, the theorem should not be applied to probability calculations using the Essen-Möller's formula. 3) A new basis of judgement for the diagnosis of paternity is proposed using the probability distribution of the relative frequencies of log (Y/X) for true father and that for non-father.

Blood Group Antigens↗
PubMed1999

Biological probability: cognitive processes of generating probabilities of events in biological systems.

This paper analyses relationships between probabilities of events happening in biological systems (or probabilistic disposition of systems) and cognitive properties of biological entities comprising such systems. Two kinds of cognitive properties are identified as relevant to the current problem: the ability to respond differently against different configurations of the environment (discriminability of cognition), and the ability to make an appropriate response to maintain a particular relation with the environment (selectivity of cognition). A basic framework bridging the two features of living systems, probabilistic disposition and the cognitive properties, is presented towards a general theory explaining the process generating probabilities of biological events. In this framework, a deterministic model of a system of entities is developed, in which objects are described as subjects that cognize events (i.e. entities as cognizers). Cognition is used in a wider sense, including not only biotic but also abiotic, and cognizers are conceptually distinguished from the meta-observer who describes the system externally. Based on this perspective, this paper seeks to explicate how events can occur in an uncertain, probabilistic manner, if observed from a cognizer viewpoint, even under a deterministic system. Each cognizer is identified with both the set of states that are actually taken, and its motion function which maps its state uniquely to a successor state depending on the current states of itself and of the rest of cognizers constituting the system. The model analysis reveals that the cognitive properties, discriminability and selectivity, of a cognizer can contribute to determining the probability of an event encountered by the cognizer itself-in particular, discrimination reducing the uncertainty in events occurrence for the cognizer. Biological implication of this result is discussed focusing on the concept of the probability of survival and reproduction.

Animals↗
PubMed2005

Probability of real-time detection versus probability of infection for aerosolized biowarfare agents: a model study.

Real-time biosensors are expected to provide significant help in emergency response management should a terrorist attack with the use of biowarfare, BW, agents occur. In spite of recent and spectacular progress in the field of biosensors, several core questions still remain unaddressed. For instance, how sensitive should be a sensor? To what levels of infection would the different sensitivity limits correspond? How the probabilities of identification correspond to the probabilities of infection by an agent? In this paper, an attempt was made to address these questions. A simple probability model was generated for the calculation of risks of infection of humans exposed to different doses of infectious agents and of the probability of their simultaneous real-time detection/identification by a model biosensor and its network. A model biosensor was defined as a single device that included an aerosol sampler and a device for identification by any known (or conceived) method. A network of biosensors was defined as a set of several single biosensors that operated in a similar way and dealt with the same amount of an agent. Neither the particular deployment of sensors within the network, nor the spacious and timely distribution of agent aerosols due to wind, ventilation, humidity, temperature, etc., was considered by the model. Three model biosensors based on PCR-, antibody/antigen-, and MS-technique were used for simulation. A wide range of their metric parameters encompassing those of commercially available and laboratory biosensors, and those of future, theoretically conceivable devices was used for several hundred simulations. Based on the analysis of the obtained results, it is concluded that small concentrations of aerosolized agents that are still able to provide significant risks of infection especially for highly infectious agents (e.g. for small pox those risk are 1, 8, and 37 infected out of 1000 exposed, depending on the viability of the virus preparation) will remain undetected by the present, most advanced, or even future, significantly refined real-time biosensors.

Aerosols↗
PubMed2003

Infection Probability Score (IPS): A method to help assess the probability of infection in critically ill patients.

OBJECTIVE: To develop a simple score to help assess the presence or absence of infection in critically ill patients using routinely available variables. DESIGN: Observational study of a prospective cohort of patients divided into a developmental set (n = 353) and a validation set (n = 140). SETTING: Department of intensive care at an academic tertiary care center. PATIENTS: Four hundred and ninety-three adult patients admitted to the intensive care unit for > or =24 hrs. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The presence of infection was defined using the Centers for Disease Control definitions. Body temperature, heart rate, respiratory rate, white blood cell count, and C-reactive protein concentrations were measured, and the Sequential Organ Failure Assessment score was calculated throughout the intensive care unit stay. Infection was documented in 92 of the 353 patients (26%) in the developmental set and in 41 of the 140 patients (29%) in the validation set. Univariate logistic regression was used to select significant predictors for infection. Each continuous predictor was transformed in a categorical variable using a robust locally weighted least square regression between infection and the continuous variable of interest. When more than two categories were created, the variable was separated into iso-weighted dummy variables. A multiple logistic regression model predicting infection was calculated with all the variables coded 1 or 0 allowing for relative scoring of the different predictors. The resulting Infection Probability Score consisted of six different variables and ranged from 0 to 26 points (0-2 for temperature, 0-12 for heart rate, 0-1 for respiratory rate, 0-3 for white blood cell count, 0-6 for C-reactive protein, 0-2 for Sequential Organ Failure Assessment score). The best predictors for infection were heart rate and C-reactive protein, whereas respiratory rate was found to have the poorest predictive value. The cutoff value for the Infection Probability Score was 14 points, with a positive predictive value of 53.6% and a negative predictive value of 89.5%. Model performance was very good (Hosmer-Lemeshow statistic, p =.918), and the areas under receiver operating characteristic curves were 0.820 for the developmental set and 0.873 for the validation set. CONCLUSIONS: The Infection Probability Score is a simple score that can help assess the probability of infection in critically ill patients. The variables used are simple, routinely available, and familiar to clinicians. Patients with a score <14 points have only a 10% risk of infection.

Adult↗
PubMed1990

Is probability sampling always better? A comparison of results from a quota and a probability sample survey.

Two surveys in the same defined population in Sydney's western suburbs in 1986 and 1987 provided the opportunity to compare results obtained from a quota and a probability sample survey. These surveys were designed to provide information for the planning of local health promotion programs. The quota sample survey was conducted in shopping centres and used quota sampling to select 1727 respondents. In the second survey, area probability sampling was used to select 484 respondents. This survey had a response rate of 65 per cent. There were 15 questions common to both surveys; results of only three differed significantly (p less than 0.05) between surveys. None of these differences was important from a public health perspective. The agreement between the results of these two surveys probably reflects the fact that the same selection bias has operated in both. Unless a very high response rate can be achieved, quota sample surveys with age and sex quota controls may be an acceptable alternative to probability sample surveys for gathering local data relevant to the development of health programs.

Adult↗
PubMed2001

The probability-outcome correspondence principle: a dispositional view of the interpretation of probability statements.

This article presents a framework for lay people's internal representations of probabilities, which supposedly reflect the strength of underlying dispositions, or propensities, associated with the predicted event. From this framework, we derive the probability-outcome correspondence principle, which asserts that strong dispositions should lead to (1) strong (forceful) and (2) immediate outcomes and, hence, be characterized by high probabilities. In contrast, weak dispositions lead to (1) weak (fragile) and (2) delayed outcomes and are thus associated with low probabilities. We describe six experiments designed to test the correspondence principle. In the final discussion, we examine the implications of the proposed framework, from both a normative and a descriptive viewpoint.

Adult↗
PubMed2005

Preliminary results of a withdrawal and detoxification therapeutic regimen in patients with probable chronic migraine and probable medication overuse headache.

Chronic migraine (CM) is an invalidating condition affecting a significant population of headache sufferers, frequently associated with medication overuse headache (MOH). Controlled trials and guidelines for the treatment of MOH are currently not available. We studied the efficacy of a therapeutic regimen for the withdrawal of the overused drug and detoxification in a sample of patients suffering from probable CM and probable MOH during admission in eight hospitals of Piemonte-Liguria-Valle d'Aosta. Fifty patients, 42 females (84%) and 8 males (16%), mean age at observation 50.66+/-13.08 years, affected by probable CM and daily medication overuse following IHS diagnostic criteria were treated as inpatients or in a day hospital. Headache index (HI) and daily drug intake (DDI) were used for evaluating the severity of headache and medication overuse. The patients were treated by abrupt discontinuation of the overused drug and by a therapeutic protocol including i.v. hydration, dexamethasone, metoclopramide and benzodiazepines for 7-10 days. Prophylactic medication was started immediately after admission. Analgesics or triptans were used under medical control only in cases of severe rebound headache. Diagnostic protocol included routine blood tests (at admission and at discharge), dosage of B12 and folic acid. Patients underwent follow-up controls one, three and six months after discharge. The initial diagnosis was probable CM in almost all patients included in the study (41 patients); in nine patients the diagnosis was not specified (coded only as CDH). The overused medications were simple analgesics in 17 cases (34%), combination analgesics in 19 cases (38%), triptans alone or with analgesics in 13 cases (26%) and ergotamine in 2 cases (4%). We collected data from 39 patients at first follow-up (1 month), 32 after 3 months and 14 after 6 months. Mean HI was 0.91 at admission, 0.22 at discharge, 0.38 after 30 days, 0.46 after 3 months and 0.48 after 6 months. Mean DDI was 2.80 at admission, 0.39 at discharge, 0.41 after 1 month, 0.52 after 3 months and 0.59 after 6 months. These results are on average positive and tend to remain stable with time. Although preliminary and obtained on a limited number of patients at 6-month follow-up, our results seem to be encouraging about the use of the proposed therapeutic protocol.

Adult↗
PubMed2006

Excluding pulmonary embolism at the bedside with low pre-test probability and D-dimer: safety and clinical utility of 4 methods to assign pre-test probability.

INTRODUCTION: Less than 35% of patients suspected of having pulmonary embolism (PE) actually have PE. Safe bedside methods to exclude PE could save scarce health care resources if they exclude large proportions of patients with suspected PE and are widely applicable. Non-Elisa D-dimer in combination with pre-test probability of suspected PE can safely exclude PE at the bedside. Pre-test probability can be assigned by gestalt or by using clinical models (Wells, Wicki, Rodger). MATERIALS AND METHODS: We combined two databases from studies of patients with suspected PE and retrospectively compared the diagnostic test characteristics of the different methods of assigning pre-test probability. RESULTS: 535 patients were studied. PE was confirmed in 20.8% of study patients. Two clinical predictive models (Rodger and Wells) and overall diagnostic impression have similar sensitivities ranging from 96% (95% confidence interval (CI) 89-99%) to 99% (93-100%). Wicki's model has a sensitivity of 89% (77-96%). The Wells' model with a cutoff of less than 2 points in association with semi-quantitative D-dimer has a specificity of 11% (CI 7-15%). The specificities for the other clinical predictive model are ranging from 21% (17-25%) to 49% (CI 42-55%). CONCLUSION: Semi-quantitative D-dimer must be combined with safe clinical probability assessment to safely exclude PE in a significant proportion of patients. Wicki's model in association with semi-quantitative D-dimer has the lowest sensitivity and should be used carefully to exclude PE at the bedside. The Wells' model with a cutoff of less than 2 points when combined with semi-quantitative D-dimer excluded very few patients and therefore limits its clinical utility.

Aged↗