SEARCH · PubMed Health

Results for “Probability”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 415 records · Page 23Linked to original sources

PubMed2000

Using probability of persistence to identify important areas for biodiversity conservation.

Most attempts to identify important areas for biodiversity have sought to represent valued features from what is known of their current distribution, and have treated all included records as equivalent. We develop the idea that a more direct way of planning for conservation success is to consider the probability of persistence for the valued features. Probabilities also provide a consistent basis for integrating the many pattern and process factors affecting conservation success. To apply the approach, we describe a method for seeking networks of conservation areas that maximize probabilities of persistence across species. With data for European trees, this method requires less than half as many areas as an earlier method to represent all species with a probability of at least 0.95 (where possible). Alternatively, for trials choosing any number of areas between one and 50, the method increases the mean probability among species by more than 10%. This improvement benefits the least-widespread species the most and results in greater connectivity among selected areas. The proposed method can accommodate local differences in viability, vulnerability, threats, costs, or other social and political constraints, and is applicable in principle to any surrogate measure for biodiversity value.

Conservation of Natural Resources↗

PubMed2004

Scenario tree modeling to analyze the probability of classical swine fever virus introduction into member states of the European Union.

The introduction of classical swine fever virus (CSFV) into a country free of disease without vaccination may have huge consequences in terms of both disease spread and economic losses. More quantitative insight into the main factors determining the probability of CSFV introduction (PCSFV) is needed to optimally use resources for the prevention of CSFV introduction. For this purpose a spreadsheet model was constructed that calculates the annual PCSFV into member states of the European Union (EU). The scenario pathway approach was used as most probabilities in the model are very small. Probability distributions were used to take into account inherent variability of input parameters. The model contained pathways of CSFV introduction including the import of pigs and pork products, returning livestock trucks, and contacts with wild boar. All EU member states were included as possible sources of CSFV. Default results for the Netherlands showed a mean overall annual PCSFV of approximately 0.06, indicating that the Netherlands can expect CSFV introduction on average once every 18 years from the pathways and countries included in the model. Almost 65% of this probability could be attributed to the pathway of returning livestock trucks. The most likely sources of CSFV introduction were Germany, Belgium, and the United Kingdom. Although the calculated probabilities were rather low when compared with expert estimates and recent history, the most likely causes of CSFV introduction indicated by the model were considered to be realistic. It was therefore concluded that the model is a useful tool to structure and analyze information for decision making concerning the prevention of CSFV introduction.

Animals↗

PubMed1992

Taking attention to task: P300, task response probability, and within-category deviation detection.

Previously, we reported enhanced P3 amplitudes to between-category deviations among high and low probability events. Here, we tested the effects of a within-category difference. Subjects performed a go/no-go button press task as they viewed repeated, randomly-ordered presentations of nine double-digit numbers. Eight numbers fell within a prescribed range (42-49, standards); prior to testing, subjects selected one standard number for later recall. A ninth, out-of-range (91, deviant) number was also included. Subjects were tested under two conditions, in which they responded either to one (low response probability) or to seven (high response probability) standard nonselected numbers, designated as targets. Relatively larger P3s were consistently apparent only when the deviant nontarget was associated with a low probability response to a nontarget. There was a selective effect of nontarget response probability on P3 amplitude to the deviant nontarget. Our results indicate that within-category deviation detection is facilitated by "controlled" attention to the structure of the stimulus field.

Adolescent↗

PubMed2005

Subjective and objective probability effects on P300 amplitude revisited.

Does objective probability affect P300 size independently and in addition to subjective probability? The latter was manipulated by the number of stimuli presented and classification task. Five groups saw target and frequent stimuli. Two saw these with p=.2 or .067, with two different button presses. Three groups saw two additional nontarget stimuli each with p=.067. One group pressed a different button for each stimulus. A second group pressed one button for the three oddballs, another for the frequent. A third critical group pressed one button for the target and another for other stimuli. In this group, P300 was larger for targets versus nontargets, and larger for nontargets versus frequents. Although nontargets were classified with frequents, their actual low probability distinguished them from frequents, and their subjective probability distinguished them from targets. Therefore, actual and subjective probability effects were independently found.

Adult↗

PubMed2005

Variance estimators for three "probabilities of causation".

This article introduces the definitions of three "probabilities of causation" suggested by Pearl (1999), which are used to evaluate the causal effect of an exposure on a disease in epidemiological studies. Pearl (1999) and Tian and Pearl (2000a, 2000b) provided identification formulas for three "probabilities of causation" from statistical data under some assumptions. In order to examine the estimation accuracy problem, this article derives variance estimators for three "probabilities of causation" correspondent to each case in Pearl (1999) and at the same time clarify their properties. In addition, we conduct simulation experiments and show that the proposed method can approximate sufficiently to the variance of "probabilities of causation." The results of this article provide a complete framework for using "probabilities of causation" effectively in order to analyze responsibility and susceptibility in epidemiological studies.

Analysis of Variance↗

PubMed2004

Immediate termination of fibrillation at 50% probability of overall success correlates with defibrillation dose-response curve width.

INTRODUCTION: Issues in transthoracic defibrillation, including waveform shape, fixed versus escalating dose protocol, and low- versus high-energy shocks, can be addressed by examining the defibrillation dose-response curve. We tested the hypothesis that, for commonly used defibrillation waveforms, the steepness of the overall defibrillation dose-response curve, measured as normalized curve width, correlates with the probability of a successful defibrillation being immediate at the shock intensity producing 50% success. METHODS AND RESULTS: We used 16 isolated rabbit hearts to determine probability of overall success as a function of shock intensity and probability that a successful defibrillation is immediate rather than progressive (followed by several extrasystoles) at the shock intensity producing 50% overall defibrillation success. Two waveform pairs were tested--a monophasic damped sine versus a biphasic truncated exponential waveform commonly used for transthoracic defibrillation, and a monophasic/biphasic truncated exponential waveform pair similar to those used in internal cardioverter defibrillators. There was a close correlation between probability of a successful defibrillation being immediate at 150 and normalized curve width for the defibrillation dose-response curve. CONCLUSION: Our findings suggest that a high probability of successful defibrillation being immediate at low shock intensities is correlated with a narrow normalized curve width for the defibrillation dose-response curve.

Action Potentials↗

PubMed2006

Probability of exclusion in paternity testing: time to reassess.

The average exclusion probability is a measure of efficiency in paternity testing; it refers to the a priori ability of a battery of tests to detect paternity inconsistencies. This parameter measures the capacity of the system to detect a false accusation of paternity. Traditionally, this average exclusion probability has been estimated as the probability of excluding a man who is not the father by an inconsistency in at least one of the studied loci. We suggest that this criterion should be corrected, as currently the presumed father is excluded when at least three genetic inconsistencies are found with the child being tested, not just one. This change of criterion has occurred because of the use of microsatellite loci, whose mutation rates are much greater than those of the coding genes used previously in paternity studies. We propose the use of the average probability of exclusion for at least three loci (not only one), as an honest measure of the combined probability of exclusion of several loci, and we propose an algebraic expression to calculate it.

False Positive Reactions↗

PubMed2002

Probabilities of progression of aortic aneurysms: estimates and implications for screening policy.

BACKGROUND: Screening for abdominal aortic aneurysm, and intervention with elective repair, can reduce the incidence of aneurysmal rupture by a half. If a screening programme is implemented, it is essential to determine appropriate follow up intervals for rescreening. This paper estimates probabilities of progression growth of aortic diameter to provide evidence for this. METHODS: Data were taken from 2342 men aged 65-80 screened in the Chichester randomised control trial, who have been followed up for an average of 11 years. Aortic diameter was modelled as a Markov process with four categories: <30 mm (normal), 30-44 mm, 45-54 mm, and > or =55 mm. Estimates of the probabilities of progressing to each higher category were obtained. RESULTS: The probabilities of progression increased with greater initial aortic diameter. The estimated rates/year were 0.018 (95% confidence interval 0.014 to 0.023), 0.16 (0.12 to 0.20), and 0.49 (0.35 to 0.70) respectively for moving up one category. The probabilities of moving from <30 mm to > or =55 mm were estimated as 1% in 5 years and 12% in 15 years, while the corresponding figures for moving from 45-54 mm to > or =55 mm were 91% and 99%. There were differences in rates of progression according to age, with men over 70 years having rates about three times those of men under 70. CONCLUSIONS: It seems unnecessary to follow up men with normal aortic diameter as they experience a low probability of reaching criteria for surgery even within 15 years. However, follow up intervals should be progressively shorter for those with greater aortic diameter, especially in those aged over 70. Active follow up, for example every 3 months, is appropriate for men with an aortic diameter of 45-54 mm.

Aged↗

PubMed2005

[Probability of developing and dying of cancer in Catalonia during the period 1998-2001].

BACKGROUND AND OBJECTIVE: We intended to estimate the probability of developing and dying from cancer in Catalonia during the period 1998-2001. PATIENTS AND METHOD: We used a Bayesian model which incorporates data from the Tarragona and Girona Cancer Registries and from the Catalonia Mortality Registry. The probability of developing and dying from cancer has been calculated using a competitive risk-based methodology. RESULTS: Lifetime probability of developing cancer in Catalonia is almost 1 out of 2 (43.7%) for men and 1 out of 3 (32.1%) in women. The probability of dying from cancer is 29.1% for men and 17.9% in women. 67% of men and 56% of women diagnosed with cancer will die from this disease. One out of 14 men will develop a lung cancer during his life and 1 out of 11 women will develop breast cancer. CONCLUSIONS: The observed rising in the probability of developing cancer in Catalonia over the last ten years highlights even more than ever the importance of this health problem.

Adolescent↗

PubMed2006

An alternative foundation for the planning and evaluation of linkage analysis. I. Decoupling "error probabilities" from "measures of evidence".

The lod score, which is based on the likelihood ratio (LR), is central to linkage analysis. Users interpret lods by translating them into standard statistical concepts such as p values, alpha levels and power. An alternative statistical paradigm, the Evidential Framework, in contrast, works directly with the LR. A key feature of this paradigm is that it decouples error probabilities from measures of evidence. We describe the philosophy behind and the operating characteristics of this paradigm--based on new, alternatively-defined error probabilities. We then apply this approach to linkage studies of a genetic trait for: I. fully informative gametes, II. double backcross sibling pairs, and III. nuclear families. We consider complete and incomplete penetrance for the disease model, as well as using an incorrect penetrance. We calculate the error probabilities (exactly for situations I and II, via simulation for III), over a range of recombination fractions, sample sizes, and linkage criteria. We show how to choose linkage criteria and plan linkage studies, such that the probabilities of being misled by the data (i.e. concluding either that there is strong evidence favouring linkage when there is no linkage, or that there is strong evidence against linkage when there is linkage) are low, and the probability of observing strong evidence in favour of the truth is high. We lay the groundwork for applying this paradigm in genetic studies and for understanding its implications for multiple tests.

Computer Simulation↗

PubMed1985

Alternative diagnostic strategies for coronary artery disease in women: demonstration of the usefulness and efficiency of probability analysis.

Alternative strategies using conditional probability analysis for the diagnosis of coronary artery disease (CAD) were examined in 93 infarct-free women presenting with chest pain. Another group of 42 consecutive female patients was prospectively analyzed. For this latter group, the physician had access to the pretest and posttest probability of CAD before coronary angiography. These 135 women all underwent stress electrocardiographic, thallium scintigraphic, and coronary angiographic examination. The pretest and posttest probabilities of coronary disease were derived from a computerized Bayesian algorithm. Probability estimates were calculated by the four following hypothetical strategies: SO, in which history, including risk factors, was considered; S1, in which history and stress electrocardiographic results were considered; S2, in which history and stress electrocardiographic and stress thallium scintigraphic results were considered; and S3, in which history and stress electrocardiographic results were used, but in which stress scintigraphic results were considered only if the poststress probability of CAD was between 10% and 90%, i.e., if a sufficient level of diagnostic certainty could not be obtained with the electrocardiographic results alone. The strategies were compared with respect to accuracy with the coronary angiogram as the standard. For both groups of women, S2 and S3 were found to be the most accurate in predicting the presence or absence of coronary disease (p less than .05). However, it was found with use of S3 that more than one-third of the thallium scintigrams could have been avoided without loss of accuracy. It was also found that diagnostic catheterization performed to exclude CAD as a diagnosis could have been avoided in half of the patients without loss of accuracy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1996

Use of the Weibull hazard model to estimate age-specific probability of permanent tooth loss.

In analysis of the probability of tooth loss with age, the exact time of tooth loss is often unknown, although it is clear whether a tooth remains or has been lost. That is, left censoring is inevitable during data sampling. This may provide a biased estimate if such data are dealt with by the product-limit method, which is a common method of survival analysis. To reduce such a bias in estimating the age-specific probability of tooth loss, we developed a survival analysis method taking left censoring into consideration. Four hundred and forty-six panoramic radiographs obtained in a daily clinical practice were used. The frequency of tooth loss with age was assumed to follow the Weibull hazard model, and a likelihood function taking left censoring into consideration was defined to estimate the probability of tooth loss. The estimate obtained from our method was compared with that from the product-limit method to examine whether the effect of left censoring was reduced. We found that the probability of tooth loss estimated by the product-limit method was biased by left-censored data, and that the bias was reduced when our method was used. A Monte Carlo simulation study, in which the true tooth loss time was given, also showed that our method provided an estimate closer to the true value. Our method is considered to be more accurate in estimating the probability of tooth loss, since it reduces the bias caused by left-censored data.

Adolescent↗

PubMedDate not supplied

The roles of experience and domain of expertise in using numerical and verbal probability terms in medical decisions.

Verbal probability terms are frequently used in medical practice. In the present experiment the use of verbal and numerical probability terms in medical decisions was investigated. Interns, residents in surgery and internal medicine, surgeons, and internists were asked to make treatment decisions for three different cases (acute appendicitis, angina pectoris, and an imaginary disease) and were also asked to give numerical interpretations of a series of verbal probability terms. In the second stage of the experiment the respondents received the same cases, but with numerical probability terms. The results showed no effect of context or of domain experience on the interpretation of verbal terms. Residents and experienced surgeons more often agreed on treatment decisions when chance information was presented in numerical terms as compared with verbal terms. Physicians were less confident when verbal terms were presented, but only for the less familiar decision problems. Finally, physicians turned out to be better in Bayesian reasoning when numerical terms were used. Experienced physicians were quite accurate in estimating the posterior probability in the appendicitis case, but not in the imaginary-disease case.

Acute Disease↗

PubMedDate not supplied

You can lead a horse to water--improving physicians' knowledge of probabilities may not affect their decisions.

OBJECTIVES: To determine whether improving physicians' judgments of the probability of streptococcal pharyngitis for patients with sore throats would affect their use of antibiotics and affect the variation in such use. DESIGN: Post-hoc retrospective analysis of data previously collected as part of a controlled trial. SETTINGS: University student health services in Pennsylvania and Nebraska. PATIENTS: Sequential patients with pharyngitis seen before and after the time clinicians received either an experimental educational intervention designed to improve probabilistic diagnostic judgments (at the Pennsylvania site) or a control intervention, a standard lecture (at the Nebraska site). The clinician-subjects were the primary case physicians practicing at either site. MEASUREMENTS: Clinical variables prospectively recorded by the clinicians, probability assessments, and treatment decisions. RESULTS: At the experimental site, despite marked decreases in clinicians' overestimations of disease probability after the intervention, the proportion of patients prescribed antibiotics showed a trend toward increasing: 100/290 (34.5%) pre-intervention, 90/225 (40%) post-intervention. The intervention did not decrease practice variation between individual doctors. Univariable and multivariable analyses showed no major change in the relationships between clinical variables and treatment decisions after the intervention. At the control site there was no major change in probability judgments or treatment decisions after the intervention. CONCLUSIONS: Teaching physicians to make better judgments of disease probability may not alter their treatment decisions.

Anti-Bacterial Agents↗

PubMed1987

The probability of cancer death in Italian males and females.

Probabilities of cancer death in Italian males and females over the calendar period 1955 to 1980 were computed from age-specific death certification rates for various neoplasms and contemporary general life tables of the whole Italian population. There were substantial increases in eventual probabilities of total cancer mortality: from 16.9 to 27.1% for males and from 15.2 to 19.3% for females. The upward trends were particularly large for lung (from 1.9 to 7.2%) and other tobacco-related sites in males. In females, the largest increases were for neoplasms of the intestines (from 1.6 to 3.0%) and breast (from 1.9 to 3.1%). Separate analyses of probabilities of cancer death in specific age intervals showed more limited changes in middle age, and some moderate decrease at younger ages, probably attributable to improved treatment. The probability estimates presented are clearly based on criticizable assumptions, since they do not allow for any potential subsequent change in mortality and are inappropriate for analyzing the evolution of cancer rates because they reflect (in opposite directions) trends in cancer mortality and in all other causes of death. Nonetheless, a correct interpretation of these estimates does provide some important information from a public health viewpoint, in terms of resource allocation and health care planning, and can help quantify the increasing demand for oncologic services and structures over the next few decades.

Actuarial Analysis↗

PubMed2005

Medical concepts related to individual risk are better explained with "plausibility" rather than "probability".

BACKGROUND: The concept of risk has pervaded medical literature in the last decades and has become a familiar topic, and the concept of probability, linked to binary logic approach, is commonly applied in epidemiology and clinical medicine. The application of probability theory to groups of individuals is quite straightforward but can pose communication challenges at individual level. Few articles by the way have tried to focus the concept of "risk" at the individual subject level rather than at population level. DISCUSSION: The author has reviewed the conceptual framework which has led to the use of probability theory in the medical field in a time when the principal causes of death were represented by acute disease often of infective origin. In the present scenario, in which chronic degenerative disease dominate and there are smooth transitions between health and disease the use of fuzzy logic rather than binary logic would be more appropriate. The use of fuzzy logic in which more than two possible truth-value assignments are allowed overcomes the trap of probability theory when dealing with uncertain outcomes, thereby making the meaning of a certain prognostic statement easier to understand by the patient. SUMMARY: At individual subject level the recourse to the term plausibility, related to fuzzy logic, would help the physician to communicate to the patient more efficiently in comparison with the term probability, related to binary logic. This would represent an evident advantage for the transfer of medical evidences to individual subjects.

Chronic Disease↗

PubMed1996

Analysis of cumulative probabilities shows that the efficacy of 5HT3 antagonist prophylaxis is not maintained.

PURPOSE: Several investigators have reported that the efficacy of 5HT3 receptor antagonists is maintained over repeated cycles of chemotherapy. These investigators presented conditional probabilities of protection. Because conditional analyses by definition only include patients with protection in previous cycles, the results are flattered. PATIENTS AND METHODS: We applied a novel statistical approach to investigate whether the efficacy of the 5HT3 receptor antagonist ICS 205-930 (tropisetron) is maintained over repeated cycles of weekly high-dose cisplatin. Overall protection was determined based on cumulative probabilities with the Kaplan-Meier method. Complete protection was calculated with a three state model for transitional probabilities. Eighty-three patients were studied. RESULTS: Over six consecutive cycles, protection against both acute and delayed emesis decreased significantly. The initial complete and overall protection rates against acute emesis of 71% and 95%, respectively, decreased to 43% and 72% in the sixth cycle of chemotherapy. Similarly, the protection rates of 31% and 68% against delayed emesis decreased to 6% and 40%, respectively. CONCLUSION: We conclude that overall and complete long-term protection is more accurately measured by cumulative probabilities than with a method that is based on conditional probabilities. Our statistical approach shows that the efficacy of 5HT3 antagonists is not maintained.

Adult↗

PubMed2006

Effects of phonotactic and orthotactic probabilities during fast mapping on 5-year-olds' learning to spell.

The purpose of this study was to investigate the orthographic-processing skills of typically developing 5-year-old preschool children. Of interest was whether phonotactic probabilities and/or orthotactic probabilities affected their ability to quickly learn the orthographic forms of 12 novel words. Orthographic processing was measured by the children's ability to spell and identify spellings of the novel words. Specifically, we were interested in whether (a) children quickly stored or "fast mapped" orthographic information after minimal exposure to novel words during storybook readings, (b) phonotactic and orthotactic probabilities affected orthographic fast-mapping skills, and (c) orthographic processing explained unique variance on a measure of the children's early spelling abilities. The results of this study indicated that young children quickly fast mapped orthographic information after minimal exposure to novel words, and their spelling (generation or reproduction but not recognition) was influenced by phonotactic and orthotactic probabilities. The significance of this work is that it demonstrates that preschoolers can fast map orthographic words they see onto spoken words they hear while listening to storybooks read to them and that the spelling of preschoolers is influenced uniquely by both phonological and orthographic information (probability of frequent letter and sound sequences in English words).

Child↗