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PubMed2000

Using electronic data to predict the probability of true bacteremia from positive blood cultures.

As part of a project to help physicians make more appropriate treatment decisions, we implemented a clinical prediction rule that computes the probability of true bacteremia for positive blood cultures and displays this information when culture results are viewed online. Prior to implementing the rule, we performed a revalidation study to verify the accuracy of the previously published logistic regression model. We randomly selected 114 cases of positive blood cultures from a recent one-year period and performed a paper chart review with the help of infectious disease experts to determine whether the cultures were true positives or contaminants. Based on the results of this revalidation study, we updated the probabilities reported by the model and made additional enhancements to improve the accuracy of the rule. Next, we implemented the rule into our hospital's laboratory computer system so that the probability information was displayed with all positive blood culture results. We displayed the prediction rule information on approximately half of the 2184 positive blood cultures at our hospital that were randomly selected during a 6-month period. During the study, we surveyed 54 housestaff to obtain their opinions about the usefulness of this intervention. Fifty percent (27/54) indicated that the information had influenced their belief of the probability of bacteremia in their patients, and in 28% (15/54) of cases it changed their treatment decision. Almost all (98% (53/54)) indicated that they wanted to continue receiving this information. We conclude that the probability information provided by this clinical prediction rule is considered useful to physicians when making treatment decisions.

Algorithms↗

PubMed1975

The attainment of formal operations: a comparison of probability concepts in deaf and hearing adolescents.

In a series of six experiments deaf and hearing adolescents were compared on attainment of formal operations in Piaget's theory as represented by performance on probability problems. Performance of deaf subjects provided a desirable control comparison, since their knowledge of probability concepts was most likely acquired outside school classrooms. The probability problems were usually binary choice situations that required no verbalizations and were designed to illuminate strategies, as well as to indicate conceptual stage. Two experiments, one a long-term training study of over two years' duration, used supplementary preadolescent subject groups. Most of the hearing adolescents and many of the deaf adolescents attained the formal operatory level for probability concepts according to the criteria described by Piaget and Inheldermtheir criteria can be criticized, however, as insufficiently demanding, although they do point up the difficulty of defining the place of computational abilities in formal operationsmresults from several experiments suggested a second and higher level of formal operatory attainment around the ages of 14 to 15. Further theoretical insights were obtained regarding the implicit rules that frequently appeared to guide subjects' choices; a surprising variety of strategies were reported. Analysis of choice tendendies showed consistent avoidance of calculations and selection of the choice with the greatest absolute rather than relative frequency (or area) even when these strategies produced systematic errors. Subjects were generally unable to combine probability information from two different sources. In the long-term training experiment spontaneous improvement was shown by children at formal operatory ages even without training, but not by younger children. Deaf adolescents performed as well as hearing adolescents on easy problems, but they made more errors on several types of more difficult problems; Deaf adolescents were also less consistent than the hearing in use of rules, and in several experiments they showed a two- to three-year performance lag.

Achievement↗

PubMed2003

Ruling out clinically suspected pulmonary embolism by assessment of clinical probability and D-dimer levels: a management study.

D-dimer test combined with clinical probability assessment has been proposed as the first step in the diagnostic work-up of patients with suspected pulmonary embolism (PE). In a prospective management study we investigated the safety and efficiency of excluding PE by a normal D-dimer combined with a low or moderate clinical probability. Of the 202 study patients this combination ruled out PE in 64 (32%) patients. The 3-month thromboembolic risk in these patients was 0% (95% CI, 0.0-5.6%). The prevalence of PE in the entire cohort was 29% (59 patients), whereas in the low, moderate and high clinical probability groups this was 25%, 26% and 50%, respectively. We conclude that ruling out suspected PE by a normal D-dimer combined with a low or moderate clinical probability appears to be a safe and efficient strategy. The accuracy of the clinical probability assessment is modest.

Adult↗

PubMed1992

[Investigation of algorithm for the calculation of probability of paternity likelihood using personal computer program, including the application to parentage testing in the decreased party].

Algorithm for the computerized calculation of probability of paternity likelihood was investigated. The probability is calculated by Essen-Möller's formula as W = X/(X+Y) = 1/(1 + Y/X). The X value is also given as X = Hl, m, n/Kl, m, where kl, m and Hl, m, n are the probabilities of mother-child and mother-child-father combinations, respectively. In this study, four functions as F(PQ) = [1-(P not equal to Q)] x p x q, Z(RS) = (1- (R = S)), K(PQ,RS) = 1/2([(R = P) + (R = Q)].s + [(S = P) + (S = Q)].r).F (PQ)/Z(RS) and H(PQ, RS, TU) = 1/4([(R = P) + (R = Q)] [(S = T) + (S = U)] + [(S = P) + (S = Q)] [(R = T) + (R = U)]) x F(PQ).F(TU)/Z(RS) were created, where PQ, RS and TU were the genotypes of mother, child and the alleged father, P, Q, R, S, T and U were their alleles, and p, q, r, s, t and u were the allele frequencies. The equality or inequality in parenthesis was the relation operator which gave -1 or 0 when the expression was true of false, respectively. Then, three formulae as Y = n sigma k = l F([TU]k), Kl, m = 1 sigma i = l m sigma j = l K ([PQ]i, [RS]j) and Hl, m, n = l sigma i = l m sigma j = l n sigma k = l H([PQ]i, [RS]j, [TU]k) were obtained, where [PQ]i, [RS]j and [TU]k were one of the mother's, one of the child's and one of the putative father's genotypes considered from their phenotypes, respectively. Using these formulae, the probability of paternity likelihood could be calculated in every case. These formulae were programmed in BASIC language using a personal computer. Algorithm for the calculation of the probability in the deceased party was also investigated.

Algorithms↗

PubMedDate not supplied

[The use of the probability model for an estimation of a infection rate of White Sea mussels (MYtilus edulis) by Metacercariae Himasthla elongata (Trematoda: Echinostomidae) ].

A comparison of simple probability analytic model of infection rate depending on host's age with natural infection rate of mussels (Bivalvia: Mythilidae) with metacercariae Himasthla elongata (Trematoda: Echinostomidae) was carried out. Data on the natural rate of infection were accumulated during 3 years; 1152 individuals M. edulis were collected in two horizons within fucoid zone of the Kruglaya inlet and the Chupa inlet of the Kandalaksha bay (White Sea). A size of shell and number of H. elongata metacercariae were defined for each mussel using compressive dissection technique. The infection of mussels per year within our model is considers as independent evens: Pn = 1 - (1 - p)n, where n is the age of mussels, Pn is the theoretical part of infected n-year mussels, p is the probability of infection within one year. The probability of infection within year is assumed equal for every age of host. The estimate of probability of infection per year on the basis of sample of n-year's mussels was calculated as Pn = 1 - n square root of 1 - I(n), where n is the age of mussels, I(n) is the part of infected n-year mussels. The retransformed weighted average value of aresine-transformed p'n was used as p in our model (p = 0.3476). Statistically significant differences between empirical and theoretical (calculated from our models on the basis this value) infection rates were not found (P > > 0.05 chi 2-test). Moreover, statistical significant differences were absent (P > 0.05 Fisher exact test) in pairwise comparisons between empirical and theoretical infection rates for each age of mussels. The model does not take into consideration an effect of such factors as host's resistance, host's migration and increase of mortality in infected hosts. The absence of significant differences between the empirical and theoretical infection rates allows to suggest, that mentioned factors under the conditions of the Kruglaya inlet do not influence essentially onto infection of mussels with metacercariae H. elongata. This conclusions is in certain inconsistency with essential differences in such characteristic as an individual resistance of mussels to the infection with metacercariae H. elongata, detected in experiments in vitro (Gorbushin, Levakin, unpublished data). Analysis of intensity of the invasion of metacercariae H. elongata into mussels allows to suggest the existence of differential death rate of the hosts, which is exhibited in individuals over 7 years old. Studied example of mussels infected with metacercariae H. elongata under conditions of the Kruglaya inlet shows that the simple probabilistic model of the natural infection rate is usable for this kind of investigation. Our study also allows to conclude that in this case the infection rate of hosts is mainly determined by stochastic reasons. However, in some cases the probability of infection rate may not depend on the age and size of the host. The study of infection rate can not be used for analyses of individual differences of hosts in a resistance to parasites and an infection ability of the parasite.

Age Factors↗

PubMed1992

Probability estimation for biomedical classification problems.

Suppose that we wish to know the probability that an object belongs to a class. For example, we may wish to estimate the probability that a patient has a particular disease, given a set of symptoms, or we may wish to know the probability that a novel peptide binds to a receptor, given the peptide's amino-acid composition. The conventional approach is to first use a classification algorithm to find partitions in feature space and to assign each partition to a class, and then to estimate the conditional probabilities as the proportion of patients or peptides that are correctly and incorrectly classified in each partition. Unfortunately, this estimation method often gives probability estimates that are in error by 20% or more, and thus can cause incorrect decisions. We have implemented and compared alternative methods. In Monte Carlo simulations the alternative methods are substantially more accurate than is the current method.

Epidemiology↗

PubMed2004

Pretest probability estimates: a pitfall to the clinical utility of evidence-based medicine?

OBJECTIVES: The Bayesian application of likelihood ratios has become incorporated into evidence-based medicine (EBM). This approach uses clinicians' pretest estimates of disease along with the results of diagnostic tests to generate individualized posttest disease probabilities for a given patient. To date, there is minimum scientific validation for the clinical application of this approach. This study is designed to evaluate variability in the initial step of this process, clinicians' estimates of pretest probability of disease, to assess whether this approach can be expected to yield consistent posttest disease estimates. METHODS: This cross-sectional cohort study was conducted at an urban county teaching hospital by using a sample of emergency and internal medicine residents and faculty, as well as emergency department (ED) midlevel practitioners. Participants read clinical vignettes designed to raise consideration for common ED disorders and were asked to estimate the likelihood of the suggested diagnosis based on the history and physical examination findings alone. No information about laboratory results or imaging studies was provided. RESULTS: Mean pretest probability estimates of disease ranged from 42% (95% confidence interval [95% CI] = 36.6% to 47.4%) to 77% (95% CI = 72.9% to 81.1%). The smallest difference in pretest probability magnitude for a single vignette was 70% (range 30-100%; interquartile range [IQR] 64-80%), whereas the largest was 95% (range 3-98%; IQR 30-60%). CONCLUSIONS: Wide variability in clinicians' pretest probability estimates of disease may present a possible concern about decision-making models based on Bayes' theorem, because it may ultimately yield inconsistent posttest disease estimates.

Bayes Theorem↗

PubMedDate not supplied

A comparison of neural networks for computing predicted probability of survival for trauma victims.

TRISS is a statistical method for predicting the probability of survival of trauma victims. Analysis of data from the Trauma Registry at Charleston Area Medical Center showed that only 48% of the trauma fatalities in the 5-year period 1992-1996 were correctly predicted by TRISS. Trauma practitioners from other Trauma Centers report similar problems with TRISS. Researchers have suggested improvements that range from simply changing the input variables and/or regression coefficients in TRISS to using an entirely different model. In this study we describe a method of calculating survival probabilities using Artificial Neural Networks (ANN). This method was chosen because of the similarity of the ANN output function to the function that produces the TRISS probability of survival. Additional variables were added based on the results of other research efforts as well as analysis of the CAMC Trauma Registry. A comparison was made between the abilities of TRISS to predict fatalities and to approximate probability of survival. The ANN outperformed TRISS in predicting fatalities in a training set (68.1% correct vs. 47.9% correct) and in a testing set (61.3% correct vs. 51.3% correct). More importantly, the ANN produced better estimates of predicted deaths. Using a data set that included 119 deaths, the ANN model predicted 125 deaths for a 5% relative error. The predicted number using TRISS was 86 for a relative error of 27.7%. Since effective quality improvement for trauma care depends on accurately identifying cases that fall outside the expected results, a more accurate predictive tool allows a more focused review of those significant cases, thus conserving resources without compromising quality. Neural Networks appear to be a predictive tool that can provide probability of survival estimates that are more accurate than TRISS.

Humans↗

PubMedDate not supplied

[The relation of the typological classification of dogs to their behavioral characteristics in variations between the probability and the value of reinforcement].

In studying of dogs behaviour in coordinates system "Requirements and probability of their satisfaction" it has been established that selection of behaviour strategy is closely connected with individual typological properties of animals. In experiments with equally-probable alimentary reinforcement a direct correlation was found between the strength parameter of the nervous system and the strategy of dogs behaviour. Animals of strong types manifested the character of reaction which consisted in determination and goal-directedness, while the animals of the weak type manifested other character, having features of uncertainty, indefinition, hesitations. In conditions of conflict between probability and value of reinforcement the dogs manifested two opposite strategies of behaviour: orientation to highly probable events (choleric and phlegmatic) and to low-probable events (sanguinic and melancholic) what is connected with individual properties of functioning and the character of interaction of four brain structures (frontal cortex, hippocampus, hypothalamus, amygdala).

Animals↗

PubMedDate not supplied

[Problems of assessing sibship probabilities by means of genetic analysis].

Nowadays, kinship studies based only on STR analysis are a very common practice. Apart from regular paternity cases, there is a rising number of cases in which the type of sibship between two persons has to be determined. Very often the parents or further relatives are unavailable for testing, so that the probability e. g. for a half-sibship has to be calculated as a deficiency situation. 50 unrelated persons (Group 1), 50 full siblings (Group 2), and 50 half-siblings (Group 3) were genotyped using the 15 STRs comprised by the AmpFlSTR Identifiler multiplex PCR-kit to investigate the reliability of common statistics programs and the indicative value of the calculated probabilities. Using a commercially available statistics program, we calculated probabilities for the following hypotheses: 1. The persons investigated are full siblings; 2. the persons investigated are half-siblings; 3. the persons investigated are unrelated. After STR analysis, half-sibling probabilities between 0.03 %-97.56% for group 1, between 0.01%-78.46% for group 2, and between 24.28%-90.18% for group 3 were calculated. In addition, the authors present two complicated deficiency cases which could be resolved only by extensive DNA typing using X- and Y-chromosomal loci, respectively, as well as the investigation of further relatives. The results of this study suggest that typing of autosomal STRs alone is no sufficient tool for resolving cases of possible half-sibship, even if probabilities of more than 90.0% are obtained. Due to the results of our study we suggest the implementation of mandatory standards for the investigation and interpretation of complicated kinship cases.

Adult↗

PubMed1991

[Empirical estimation of recurrence risks in multifactorial diseases with variable age-at-onset: conditional probability approach].

Conditional probability approach in estimation of recurrence risks considered in the report is naturally extended to the case of diseases with variable age-at-onset which are divided into many age-at-onset incompatible classes, the distribution of families for classes of affected and normal siblings being polynomial, modified with regard both for classes by age manifestation and for age of relatives at the moment of observation. This case is realised within the framework of the so called "life-table" approach of general use in demography. It is emphasized that the estimate of "accumulated morbidity" obtained within this framework--as a resulting estimate of "forthcoming risk" for individuals which are at premanifestational age--is the "a posteriori" probability for relatives to be affected by the disease. It is indicated that conditional probability approach, being free of any biological models of the disease origin, is not free of ascertainment models: different kinds of stratifications of the patients for the features related to their ascertainment as probands (age-at-onset, age by the time of observation, sex, birth order, etc.) can naturally generate inconsistency of the ascertainment probability pi both within and among the families, violating the independence of the ascertainment of patients as probands. In this connection, the maximum likelihood equations are given for estimation of the ascertainment probabilities of different incompatible groups of patients as probands and the necessity to account for possible differences in pi-s is pointed out.

Age Factors↗

PubMed1989

The probability of causation under a stochastic model for individual risk.

In this paper we offer a mathematical definition for the probability of causation that formalizes the legal and ordinary-language meaning of the term. We show that, under this definition, even the average probability of causation among exposed cases is not identifiable from epidemiologic data. This is because the probability of causation depends both on the unknown mechanisms by which exposure affects disease risk and competing risks, and on the unknown degree of heterogeneity in the background disease risk of the exposed population. We derive the maximum and minimum values for the probability of causation consistent with the observable population quantities. We also derive the relationship of the "assigned share" (excess incidence rate as a proportion of total incidence rate) to the probability of causation.

Biometry↗

PubMed1989

[Playing with probabilities in dentistry].

Dependent from the probabilities of success and failure, one takes risks in daily live. These probabilities are in some instances easily estimated, in other circumstances more difficult to determine. The latter holds especially true in case of 'conditional' probabilities. In regard to dentistry, these probabilities are of importance too; if, for instance, one has to choose between endodontic treatment versus extraction, obliteration of the rootcanal and periapical pathologic processes posses a negative influence on success. This article describes how a probability is changed when a condition datum is assimilated, with use of fictive examples.

Defensive Medicine↗

PubMedDate not supplied

[Elements of probability calculation--II].

This is the second part of an introduction to probability calculation and covers basic concepts such as conditional and simple probabilities and independent events and also a definition of two fundamental laws, those of addition and multiplication, which permit a correct combination of probabilities. Explanation of probability concepts and ideas is illustrated with the aid of examples from the field of screening tests. Bayes theorem is derived by applying the addition and multiplication laws to conditional and simple probabilities.

Bayes Theorem↗

PubMed1985

The effect of differences in gene frequency on probability of paternity.

Knowledge of gene frequencies in populations is required for the calculation of probability of paternity. The question remains open as to the degree of accuracy of gene frequency estimates required to give accurate probability of paternity figures. This is of special concern in the HLA system, which has haplotype frequencies known to vary in populations. This paper presents computer simulation data comparing probability of paternity calculations using HLA data from California and North Carolina. Comparisons were made between geographic regions, and between blacks and whites within a geographic region. It was found that when the absolute probability of paternity is high, the average differences induced were small, but at lower probabilities the changes can be large. Differences were most pronounced between black and white populations. Examples of individual cases are given to illustrate the huge differences that can be induced in some cases by changing gene frequency.

Child↗

PubMed1983

[Decision strategy as a function of event probability: 2. Latency of the decision and covering the field].

A fair number of studies have been conducted in order to assess the effect of event probability on decision strategy in a two choice reaction time (CRT) task. Results showed that increasing the probability of an event from 0.5 to 0.8 did not affect CRT. In fact, a significant decrease in CRT was obtained only when one of the two stimuli reached a probability of 0.9. It was concluded from these studies that subjects used a very conservative decision strategy. It should be pointed out that in these studies the instructions given to subjects emphasized both speed and accuracy of response. In many sport situations however, a player must choose speed of response over accuracy. For example the tennis player who knows that the opponent will smash the ball either to his right or hs left. The purpose of the present study was to determine whether or not in such situations the defensive player might not choose a less conservative decision strategy than that presented earlier. Fourteen subjects were submitted to a two CRT task, where the probability of each event and the time allotted (TA) to complete the appropriate response were systematically manipulated. The results obtained for each level of TA were similar to those discussed earlier. More specifically, a significant decrease in CRT was obtained only when one of the two possible events reaches a probability of 0.9. However, it appeared that, reducing TA forced subjects to reduce CRT and to base their responses more and more on anticipation than on reaction.

Decision Making↗

PubMed1980

The probability of losing an allele when diploid genotypes are sampled.

Given the genotypic frequencies for a single gene locus with an arbitrary number of alleles in a hypothetically infinite population, the probability of losing at least one of the alleles in a sample of genotypes from this population is derived. The sensitivity of this probability to changes in the population frequencies of heterozygotes and of alleles has been investigated and has proved to be in accord with intuitive expectations. Least upper bounds for this probability, in cases where only the allelic frequencies or the minimum allelic frequency of alpha is known, have been found and the correspondence of these bounds to the situation of sampling of gametes rather than genotypes has been pointed out. It has been proved that the latter bound is also the least upper bound of the probability of losing at least one of the alleles with frequencies greater than or equal to alpha in a sample of genotypes or gametes if neither the number of alleles in the population nor the genotypic frequencies are known. This result has been used for the compilation of a table of the minimum sample sizes required to assure that all alleles with frequencies greater than or equal to alpha are detected with probability 1-sigma for the different values of alpha or sigma.

Alleles↗

PubMed1995

The low-probability lung scan. A need for change in nomenclature.

BACKGROUND: The prognosis in patients with suspected pulmonary embolism who have a low-probability lung scan has been the focus of much clinical debate. This is particularly so in patients with underlying cardiac and pulmonary disease, because these disorders frequently cause low-probability lung scans in the absence of pulmonary embolism. Historically, the clinical response has been to exclude pulmonary embolism and withhold treatment on the basis of a low-probability lung scan, which has been regarded as synonymous with a good prognosis. METHODS: A prospective cohort-analytic study to evaluate prognosis, using long-term follow-up, in patients with inadequate cardiorespiratory reserve who have presented with suspected pulmonary embolism (inadequate cardiorespiratory reserve, ie, pulmonary edema, right-ventricular failure, hypotension, syncope, acute tachyarrhythmia, abnormal spirometry [forced expiratory volume in 1 second, < 1.0, or vital capacity, < 1.5 L], or abnormal arterial blood gases [PO2, < 50 mm Hg, or PCO2, > 45 mm Hg]). RESULTS: The outcomes of the 77 consecutive patients with low-probability lung scans, suspected pulmonary embolism, and inadequate cardiorespiratory reserve were compared with those in 711 consecutive patients with good cardiorespiratory reserve and nondiagnostic lung scans who were entered into the study over the same period of time. Six (7.8%) of the 77 patients died within days of entry with autopsy-proven pulmonary embolism compared with one (0.14%) of the 711 patients with nondiagnostic lung scans (P < .0001). CONCLUSIONS: Our findings indicate that the term low-probability lung scan should be abandoned in reference to patients with inadequate cardiorespiratory reserve, because it is not synonymous with a good prognosis and is, indeed, misleading.

Adult↗