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 703 records · Page 39Linked to original sources

PubMed1996

The use of dental radiographs to estimate the probability of cavitation of carious interproximal lesions. Part II: Two patient scenarios.

Diagnosis of a cavitated interproximal lesion is often not confirmed until the tooth is treated. Before treatment, clinicaians and patients are dealing with probabilities which can be estimated from clinical evidence, radiographic evidence, and information found in the dental literature. The probability of a diagnostic test result being correct is affected by the threshold of the test and the pretest probability of the disease in question, which varies with the prevalence of the disease. We illustrate how clinicians can inform themselves and their patients of the probability of a radiographic lesion being truly cavitated based on graphs that summarize the currently available evidence. Dentists who use these graphs can more accurately inform their patients who can then choose the course of care that best meets their individual needs.

Adolescent↗

PubMedDate not supplied

Survival probabilities of Pugh-Child-PBC classified patients in the euricterus primary biliary cirrhosis population, based on the Mayo clinic prognostic model. Euricterus Project Management Group.

BACKGROUND/AIMS: Estimation of prognosis becomes increasingly important in primary biliary cirrhosis (PBC) with advancing disease and also with regard to patient management. The ubiquitous used Pugh scoring for severity of disease is simple while the Mayo model which has been validated for survival estimates is more sophisticated. We wanted to investigate whether Pugh and Mayo scores correlate (they have 3 of 5 variables in common) and if so whether a survival probability based on Mayo data could be affixed on Pugh classes and scores obtained in the same patients. METHODOLOGY: All variables used for Mayo Clinic Prognostic Model (Mayo) scoring and Pugh-Child-PBC (Pugh) scoring were available in 143 PBC patients of the Pan European database Euricterus. Pugh scores P5-P15 and has classes A (P5-6), B (P7-9) and C (P10-15). We subdivided P5 in P5A (patients with albumin > 40 g/l plus prothrombin time < or = 12 secs) and P5B (the other patients in P5). We designed a category Pugh Early (PE) for patients with P5A characteristics and bilirubin < 17 mmol/l. Mayo scores R0-R15-with 1-7 years survival probabilities S-and has risk classes Low (L), Intermediate (Int), High (H) and Very High (VH). RESULTS: The estimated survival probabilities of the 143 patients ranged from 88% at 7 years to 0% at 1 year, median 14% at 5 years. The Pugh and Mayo scores correlated r = 0.87 (p < 0.0001) and except age with P, all Mayo and Pugh variables correlated with both R and P at p < 0.0001. Survival in Pugh class A was median 43% at 7 years and was not different from survival in Mayo L+Int (p 0.58). In Pugh class B 7 years survival was 2%, not different from Mayo H (p 0.25). Survival in Pugh C was median 24% at 1 years and better than Mayo VH (p 0.02). Between P5A (survival 78% at 7 yr) and R 3-4; P5B-6 (40% at 7 yr) and R5; P7 (22% at 7 yr) and R6; P8-11 (12% at 5 yr) and R7-8; and P12-14 (5% at 1 yr) and R9-10 no significant differences were found. From P8 upward there was a steep increase in death rate. PE has a 7 year survival of at least 89%. Charts of projected survival estimates for Pugh scores and classes are presented. CONCLUSION: It was possible (affixing Mayo to Pugh) to define 1-7 years survival probabilities to Pugh classes and scores for the last 7 years of the disease, i.e. the most important period for therapeutic decisions. These results need to be validated in other PBC populations.

Adolescent↗

PubMedDate not supplied

[The individual characteristics of dogs with a free choice of the probability and value of food reinforcement].

The tactics of choice between two feeders after changing the probability and quality of food reinforcement in one of them was studied in 4 freely behaving dogs. The conditioned stimulus was not changed. It was shown that choice tactics differed between the dogs even under conditions of equal 100% probability of food reinforcement in both the feeders. Decrease in probability of presentation of higher-quality food in one of the feeders increased the incidence of choice of this feeder only in one dog. This dog was characterized by a higher rate of the dynamic stereotype conditioning in response to the number of presentations of cups with food in each feeder. The dogs preferred the constant reinforcement when food in the two feeders was of the same quality but presented with different probability.

Animals↗

PubMed1998

Clinical trial designs based on sequential conditional probability ratio tests and reverse stochastic curtailing.

We propose a group sequential method based on the sequential conditional probability ratio test and show that it has the conservatism desired in practice. We also propose calculating the discordant probability, that is, the probability that the sequential test concludes differently from a fixed-sample test at the planned end of the trial, recognizing that this probability could be substantial, even if the sequential test has the same size and power as the fixed-sample size test at the planned end of the study. In addition, we show that the proposed method can be used as a stochastic curtailing tool. Thus, the method accommodates unplanned interim analyses as well as those deemed necessary based on data trends, virtually without inflating the type I error, but it is less conservative than the usual stochastic curtailing. The method is implemented through an interactive computer program.

Adrenergic beta-Antagonists↗

PubMed1994

Impairment of spatially directed attention in patients with probable Alzheimer's disease as measured by eye movements.

OBJECTIVE: To investigate changes in spatially directed attention in patients with a diagnosis of probable Alzheimer's disease (AD). BACKGROUND: Impaired attention in patients with probable AD has not been the subject of extensive research. Yet recent reports suggest that attentional deficits may be an important early feature of the disease in a subset of patients. SETTING: University hospital center studying dementia and aging. SUBJECTS: Ten mild to moderately impaired patients diagnosed as having probable AD, by National Institute of Neurologic and Communicative Diseases and Stroke criteria, and 11 healthy age- and education-matched controls. MEASURES: Eye movements were recorded as subjects participated in two experiments designed to measure spatially directed attention. Subjects were instructed to (1) attend to and fixate a target appearing randomly to the right or left of a central marker and (2) direct attention to and fixate a target appearing randomly in one of four peripheral locations. RESULTS: Patients with probable AD exhibited fewer accurate trials and longer saccade latencies in both tasks. As a group, patients performed worse in the second task that placed increased demands on attention. However, the performance of patients in this second experiment varied. Four patients performed significantly worse than all other patients, while three patients performed as well as controls. Errors in the second task were reviewed to identify specific types of attentional deficits. Six empirically derived error patterns were classified into one of two major categories: perseveration and impersistence. Seven of 10 patients made greater than 50% errors of perseveration, and three of 10 made greater than 50% errors of impersistence. CONCLUSIONS: Impairment of attention may be an early feature of AD and a prominent clinical characteristic of some patients. The differences observed in error types made by patients may reflect the varied distribution of neuropathologic changes affecting structures that mediate aspects of attention. The architecture of eye movements can be used as a physiologic measure that should provide useful information for the diagnosis and clinicopathologic subtyping of patients with AD.

Aged↗

PubMed1999

Computing probabilities of homozygosity by descent.

A person is autozygous at a locus if the person inherits the same allele twice identical by descent along two distinct paths from the same ancestor. Autozygosity is a common cause of recessive diseases in inbred populations. Homozygosity mapping uses this fact to locate the genes that cause recessive diseases. The probability of autozygosity can be used to estimate the probability of a true positive and of a false positive in homozygosity mapping. Thompson [1994] and Guo [1997] therefore studied the problem of computing the prior, unconditional (multilocus) probability of autozygosity (MPA). I consider a different quantity: the interval probability of autozygosity (IPA). The two measures are identical in the single-locus case. IPA has two notable advantages over MPA: 1. IPA does not include the possibility of heterozygous regions between the homozygous markers. 2. IPA can be computed in time that is polynomial in the pedigree size. My polynomial-time algorithm for the single-locus case solves a problem mentioned by Guo. I implemented a program to compute the IPA. The contribution of this work is the application of basic, abstract methods from computer science to address a problem in genetics.

Algorithms↗

PubMed2002

Probability distributions of enantiomeric excess in unstirred and stirred crystallization of 1,1'-binaphthyl melt.

Crystallization of 1, l'-binaphthyl from its melt can generate optical activity spontaneously. Since crystallization is a stochastic process, the enantiomeric excess (ee) generated in each crystallization varies randomly. We investigated the qualitative features of probability distribution of the ee for crystallization at two temperatures, 150 degrees C and 152 degrees C, at which conglomerate crystallization occurs. No clear transparent crystals were produced at either temperature, indicating that the solid states formed in the melt were polycrystalline. The ee randomly fluctuated from run to run, with an average of 26.9% and 2.7% when the crystallization was carried out at 152 degrees C, and 150 degrees C, respectively. The spread of the probability distribution is also substantially different. We also studied the probability distribution of ee in stirred crystallization at different stirring RPM. The results show probability distribution's broadening and evolution to a bimodality with increasing stirring RPM--a typical behavior in symmetry-breaking transitions. These results shed light on the nature of enantioselectivity in secondary nucleation and crystal growth.

Journal Article↗

PubMed1988

Predictiveness of sonographic fetal weight estimation as a function of prior probability of intrauterine growth retardation.

We evaluated the predictiveness of sonographically estimated fetal weight as a function of the estimation of probability of having intrauterine growth retardation (IUGR) before obtaining an ultrasound scan (prior probability). The value of the estimated fetal weight resided more in its high specificity than in its sensitivity, hence in its ability to confirm that the fetus is normal. The predictiveness of the method was further enhanced when the fetal weight estimation was placed in the context of the prior probability of IUGR. In particular, the positive predictive value of the test as well as the likelihood of having a growth-retarded infant in spite of an estimated fetal weight within the normal range were considerably higher as the prior probability of IUGR increased. Since the obstetrician using all available evidence is likely to form a rather good estimate of the possibility of IUGR before ordering a scan, this improvement in the predictiveness of estimated fetal weight through a Bayesian approach can be advantageously applied to ultrasound analysis and can effectively support clinical decision making.

Bayes Theorem↗

PubMed2007

Gray-scale sonography of solid breast masses: diagnosis of probably benign masses and reduction of the number of biopsies.

PURPOSE: To identify probably benign breast masses using gray-scale sonography and to see if this strategy could reduce the number of biopsies of breast masses. METHODS: This retrospective study included 229 masses in 203 women who underwent sonographically guided percutaneous biopsy. Masses with a negative predictive value for malignancy >98% were retrospectively considered probably benign, and the potential impact of gray-scale sonography in reducing the number of biopsies if these masses were not biopsied was assessed. Assessments were performed considering all masses as a group as well as various subgroups. RESULTS: Round, ellipsoid, or lobulated masses with 3 or fewer lobulations, circumscribed margins, a longitudinal-anteroposterior diameter ratio > or =1.0 and no marked hypoechogenicity, posterior acoustic shad owing, internal microcalcifications, or altered surrounding breast tissue were considered probably benign. The sensitivity of gray-scale sonography to identify this subgroup was 98%, with a negative predictive value of 99%. If these masses were not biopsied, there would be a 42% reduction in the number of biopsies considering all masses, a 36% reduction for masses classified as Breast Imaging Reporting and Data System category 4, and a 59% reduction for masses exclusively analyzed with sonography. CONCLUSIONS: It is possible to identify probably benign breast masses using gray-scale sonography, and thereby to reduce the number of biopsies performed.

Adolescent↗

PubMed1993

On the use of Bayesian probability theory for analysis of exponential decay data: an example taken from intravoxel incoherent motion experiments.

Traditionally, the method of nonlinear least squares (NLLS) analysis has been used to estimate the parameters obtained from exponential decay data. In this study, we evaluated the use of Bayesian probability theory to analyze such data; specifically, that resulting from intravoxel incoherent motion NMR experiments. Analysis was done both on simulated data to which different amounts of Gaussian noise had been added and on actual data derived from rat brain. On simulated data, Bayesian analysis performed substantially better than NLLS under conditions of relatively low signal-to-noise ratio. Bayesian probability theory also offers the advantages of: a) not requiring initial parameter estimates and hence not being susceptible to errors due to incorrect starting values and b) providing a much better representation of the uncertainty in the parameter estimates in the form of the probability density function. Bayesian analysis of rat brain data was used to demonstrate the shape of the probability density function from data sets of different quality.

Animals↗

PubMed1998

Probability of induction and stabilization of ventricular fibrillation with epinephrine.

Clinical studies suggest that epinephrine facilitates ventricular fibrillation (VF) although mechanisms remain unclear. We tested the hypothesis that epinephrine increases the probability of inducing VF and stabilizes VF in association with shortening of fibrillation action potential duration. VF was induced in isolated, New Zealand White rabbit hearts (n=16) under control conditions and in the presence of 0.9 micro M/l epinephrine. Monophasic action potentials were recorded during sinus rhythm, pacing, and fibrillation. Epinephrine reduced fibrillation p80 by 80%, from 23+/-4 to 4.6+/-1 V (P<0.05); and reduced fibrillation p90 by 82%, from 29.3+/-5.4 to 5.4+/-1.9 V (P<0.05). Epinephrine also reduced the probability of spontaneous termination of VF during the first 5 s of VF from 29 to 8% (P<0.05). Epinephrine significantly decreased mean fibrillation cycle length from 104.5+/-2 to 75.7+/-2.3 ms (P<0.001). Mean action potential duration (60% repolarization) decreased from 76+/-3 to 40+/-3 ms (P<0.0003). Frequency analysis showed a mean dominant frequency during VF of 10.0+/-0.2 Hz under control conditions and 13. 3+/-0.3 Hz with epinephrine (P<0.0001). These results suggest that epinephrine increases the probability of VF induction and decreases the probability of spontaneous defibrillation. Stabilization of fibrillation is associated with shortening of action potential duration and fibrillation cycle length, which may allow a greater number of fibrillation waves in the ventricle.

Action Potentials↗

PubMed1998

Impact of resting and ischemic blood flow on infarct probability in ischemic preconditioning--a new approach to infarct size-blood flow data by logistic regression.

The linear regression analysis of infarct size (IS) v ischemic myocardial blood flow (MBF) does not account for the heterogeneity of MBF and infarcted tissue; moreover, it cannot assess a blood flow threshold for infarction (MBFT) accurately, as with ischemic preconditioning (IP) the close relationship between ischemic MBF and IS otherwise observed is lost. Finally, the impact of resting blood flow on myocardial infarction cannot be considered in such analysis. Therefore, in a retrospective data analysis of 32 enflurane-anaesthetized swine undergoing 90 min severe ischemia and 120 min reperfusion without (CON, n = 12) or with IP induced by either 3 (IP3, n = 8) or 10 min ischemia (IP10, n = 12) and 15 min reperfusion, a MBFT was assessed by logistic regression (LR) in individual tissue pieces. MBFT was arbitrarily defined as that ischemic MBF (microspheres) at which infarct probability was 0.2, derived from the ratio of infarcted (n = 141, TTC) to all tissue samples (n = 684). The duration of the preconditioning ischemia and MBF both at rest and during the sustained ischemia were significant predictors of infarct probability. Ischemic MBFT at an infarct probability of 0.2, was 0.089 +/- 0.023 ml/min/g in CON. MBFT was decreased to 0.051 +/- 0.03 ml/min/g with IP3 (P < 0.05 v CON) and further to 0.004 +/- 0.037 ml/min/g with IP10 (P < 0.05 v CON, IP3). Corresponding to the leftward shift of MBFT, the relationships between infarct probability and MBF were shifted in parallel by IP with no change in their slopes.

Animals↗

PubMed1998

Experience-Weighted Attraction Learning in Coordination Games: Probability Rules, Heterogeneity, and Time-Variation.

In earlier research we proposed an "experience-weighted attraction (EWA) learning" model for predicting dynamic behavior in economic experiments on multiperson noncooperative normal-form games. We showed that EWA learning model fits significantly better than existing learning models (choice reinforcement and belief-based models) in several different classes of games. The econometric estimation in that research adopted a representative agent approach and assumed that learning parameters are stationary across periods of an experiment. In addition, we used the logit (exponential) probability response function to transform attraction of strategies into choice probability. This paper allows for nonstationary learning parameters, permits two "segments" of players with different parameter values in order to allow for some heterogeneity, and compares the power and logit probability response functions. These specifications are estimated using experimental data from weak-link and median-action coordination games. Results show that players are heterogeneous and that they adjust their learning parameters over time very slightly. Logit probability response functions never fit worse than power functions, and generally fit better. Copyright 1998 Academic Press.

Journal Article↗

PubMed2002

Assessing the relative contribution of individual risk factors on surgical outcome for gastric bypass surgery: a baseline probability analysis.

BACKGROUND: Multiple regression is the best technique for the simultaneous analysis of the contributions of multiple risk factors to a surgical outcome. A probability analysis is used to determine the relative contribution of individual factors to the overall outcome being assessed. We used these techniques to determine which of the potential risk factors had the greatest impact on adverse outcomes following gastric bypass surgery. METHODS: Records from 1067 consecutive patients undergoing Roux-Y gastric bypass at the UCLA Medical Center from December 1993 until June 2000 were reviewed. Major complications were used as the dependent variable in a multivariate logistic regression analysis, and 10 risk factors served as the independent variables. Based on the analysis, an average (i.e., baseline) patient was defined. Variations in the preoperative risk factors were then analyzed individually and in various combinations and their effect on the predicted probability for complication development was assessed. RESULTS: The overall major complication rate in this series was 5.8%. The average patient was defined as a 334-pound woman who was 42.3 years of age. For this patient, the predicted complication rate by probability analysis was 3.9%. The greatest increase in the anticipated complication rate was attributable to revisional procedures that increased the rate to 6.5%. Many patients have a combination of risk factors; to this end, a 62-year-old, male patient with a 2SD increase in weight (i.e., 464 pounds) who was undergoing a revision operation and had a history of smoking, hypertension, diabetes, and sleep apnea had a predicted complication rate of 33.7%. CONCLUSION: Probability analysis is a useful tool for determining the relative contribution of individual and combinations of risk factors for predicting the outcomes for surgical procedures. The four most influential factors for predicting a complication after gastric bypass surgery were; (1) male gender, (2) revisional surgery, (3) increasing age, and (4) increasing weight. These factors increased the predicted complication rate by 56, 67, 28 and 28%, respectively.

Adult↗

PubMed1994

Simple stochastic theory of stem cell differentiation is not simultaneously consistent with crypt extinction probability and the expansion of mutated clones.

It is shown that a simple Galton-Watson branching process model of the stem-cell pool in intestinal crypts is not simultaneously consistent with observations of the dynamics of replacement of normal by mutant crypt stem cells and other observations which put limits on the probability of crypt loss through extinction of all stem cells. This is because the limits on extinction probability forces the probability that a stem-cell division yields only non-stem cells to be small, but such a small probability makes it unlikely that a mutant stem-cell clone would expand while the normal stem-cell clones decay (it is more likely that both normal and mutant clones persist). It is suggested that the fundamental assumptions of independence and constancy of stem-cell behavior are flawed.

Cell Differentiation↗

PubMed2000

The Binary Additivity of Subjective Probability Does not Indicate the Binary Complementarity of Perceived Certainty.

People's numeric probability estimates for 2 mutually exclusive and exhaustive events commonly sum to 1.0, which seems to indicate the full complementarity of subjective certainty in the 2 events (i.e., increases in certainty for one event are accompanied by decreases in certainty for the other). In this article, however, a distinction is made between the additivity of probability estimates and the complementarity of internal perceptions of certainty. In Experiment 1, responses on a verbal measure of certainty provide evidence of binary noncomplementarity in the perceived likelihoods of possible scenario outcomes, and a comparison of verbal and numeric certainty estimates suggests that numeric probabilities overestimated the complementarity of people's certainty. Experiment 2 used a choice task to detect binary noncomplementarity. Soliciting numeric probability estimates prior to the choice task changed the participants' choices in a direction consistent with complementarity. Possible mechanisms yielding (non)complementarity are discussed. Copyright 2000 Academic Press.

Journal Article↗

PubMed2001

When Equal Chances = Good Chances: Verbal Probabilities and the Equiprobability Effect.

When six equally qualified candidates compete for the same position, p = 1/6 for each. People seem to accept this principle more readily for numerical than for verbal probabilities. Equal chances with three to six alternatives are often verbally described in a positive vein as "entirely possible" or "a good chance" and rarely negatively as "doubtful" or "improbable." This equiprobability effect of verbal probabilities is demonstrated in five studies describing job applicants, lottery players, competing athletes, and examination candidates. The equiprobability effect is consistent with a causal (propensity) view of probabilities, where chances are believed to reflect the relative strength of facilitating and preventive causes. If important conditions in support of the target outcome are present (the candidate is qualified for the position), and there is little to prevent it from occurring (no stronger candidates), chances appear to be good. In the presence of obstacles (one stronger candidate), or in the absence of facilitating conditions (the candidate is poorly qualified), chances appear to be poor, even when numerical p values remain constant. The findings indicate that verbal and numerical probability estimates can reflect different intuitions. Copyright 2001 Academic Press.

Journal Article↗

PubMed1994

Extremes in body mass index: probability of healthcare expenditures.

BACKGROUND: This study was conducted as a first initiative to investigate the relationship between body mass index [BMI, weight(kg)/height(m)2] and healthcare expenditures by third party providers for lifestyle-related diseases and disorders. METHOD: Data were analyzed for 383 individuals who were continuously employed and covered by the same comprehensive health insurance plan during a 2-year baseline period followed by a 5-year observation period. A multiple logistic regression analysis that adjusted for covariates was used to ascertain whether BMI and baseline expenditure status separately or in combination influenced the probability of healthcare expenditures during the observation period. RESULTS: After controlling for age, gender, and smoking status, probability of healthcare expenditures for lifestyle-related medical problems was significantly (P < 0.04) greater during the observation period for adults with high as well as low BMIs plus baseline expenditures and lowest for subjects whose BMIs were in the midrange regardless of their baseline expenditures. Odds of expenditures increased significantly (P = 0.0079) with age of nonsmokers, but was approximately constant and high for smokers at all ages. The absence of any significant interaction of either smoking status or age with BMI indicated that the relationship between BMI and the log odds of expenditures was consistent across age and smoking categories. CONCLUSIONS: The analyses support the conclusion that the highest probability of expenditures occurs with the combination of baseline insurance expenditures and BMI extremes and the lowest probability occurs when BMIs are near 26 or 27 (approximately 19% above the ideal of 22). The findings also provide further justification for focusing on extremes in body weight as health priorities.

Adult↗