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PubMed1994

Simulation of micropopulations in epidemiology: tutorial 2. Analytic forms of event probabilities. A series of tutorials illustrated by coronary heart disease models.

This is the second in a series of tutorials concerning the simulation of micropopulation models to support epidemiological research. The series emphasizes techniques that are included in studies at the National Micropopulation Simulation Resource at the University of Minnesota. For pedagogic purposes, applications to coronary heart disease models are used to illustrate the principles and methodologies employed. All of the models presented are implemented using available software. Both interpretation of the results of survey and surveillance data, and the simulation for predictive purposes of micropopulation models, depend upon the form chosen to represent the probability of the occurrence of an event associated with coronary heart disease. Four different forms are discussed; each can be used to represent the probability of transfer from the healthy state to one of the disease states or, in other words, the probability of occurrence of an event of interest. These four forms are by no means all-inclusive; rather they are ones that are convenient to use with micropopulation simulation models and that exhibit a variety of the different possibilities.

Computer Simulation↗

PubMed1995

Unrooted genealogical tree probabilities in the infinitely-many-sites model.

The infinitely-many-sites process is often used to model the sequence variability observed in samples of DNA sequences. Despite its popularity, the sampling theory of the process is rather poorly understood. We describe the tree structure underlying the model and show how this may be used to compute the probability of a sample of sequences. We show how to produce the unrooted genealogy from a set of sites in which the ancestral labeling is unknown and from this the corresponding rooted genealogies. We derive recursions for the probability of the configuration of sequences (equivalently, of trees) in both the rooted and unrooted cases. We give a computational method based on Monte Carlo recursion that provides approximates to sampling probabilities for samples of any size. Among several applications, this algorithm may be used to find maximum likelihood estimators of the substitution rate, both when the ancestral labeling of sites is known and when it is unknown.

Biological Evolution↗

PubMed1995

Influence of dimensional stability of impression materials on the probability of acceptance of a prosthetic restoration.

The accuracy of rubber impression materials was evaluated by taking impressions of a steel model, pouring it with stone and comparing certain measurements between steel and stone models. It is assumed that acceptance is achieved when the difference in measurements is within permissible limits, defined by clinical criteria. A mathematical formulation of these criteria will lead to the concept of probability of acceptance. The probability is affected when the limits are changed. The particular case of satisfying two acceptance criteria that contain variables which are not statistically independent is considered, leading to the application of the bivariate normal distribution in the evaluation of acceptance probability.

Dental Implants↗

PubMed1987

Expert medical assessment in determining probability of alleged child sexual abuse.

The purpose of this paper is to describe the role of the physician as part of the investigative team in child sexual abuse both in corroborating previously obtained disclosures and in determining the level of probability of sexual abuse where there has been no disclosure. At retrospective chart audit, history of physical and behavioral symptoms and physical and laboratory findings suggestive of child sexual abuse were correlated with allegations where known in order to classify 63 patients as to probability of sexual abuse. In this study 14.3% of cases were "unfounded" based on available evidence while 65% were "probable" or "determined." The remainder were "uncertain." Of 16 patients with physical signs, in 11 cases physical findings corroborated suspicion of child sexual abuse. The need for a systematic approach to the "directed medical interview" and examination, preferably videotaped, is discussed.

Adolescent↗

PubMed1987

Task difficulty, probability, and inter-stimulus interval as determinants of P300 from auditory stimuli.

The P300 event-related potential was elicited with auditory stimuli in 4 experiments which manipulated combinations of stimulus target probability (10% vs. 30%), task difficulty (easy vs. hard), and inter-stimulus interval (5 sec vs. 2 sec). P300 amplitude was smaller and peak latency longer for the more difficult relative to the easier tasks across experiments. Increases in stimulus target probability generally diminished P300 amplitude and shortened peak latency more for the easy relative to difficult task conditions. Increasing the number of non-target stimulus tones decreased P300 amplitude reliably, but increased latency only slightly. Task difficulty did not interact with variations in inter-stimulus interval which produced generally weak effects for both amplitude and latency. These findings suggest that P300 amplitude and latency obtained from auditory discrimination paradigms reflect processing difficulty independently of stimulus target probability unless differences in task requirements affect stimulus encoding.

Adult↗

PubMed1989

Aflatoxin is not a probably human carcinogen: the published evidence is sufficient.

Since the early 1960s, when aflatoxin, the mold-produced contaminant of a number of important food commodities, was found to be a potent hepatocarcinogen for laboratory rats, there has been a sustained search for evidence to support the regulatory presumption that aflatoxin is a probable human carcinogen. The developing laboratory evidence of differences between species in metabolism of aflatoxin and susceptibility to its oncogenic effects indicated that humans were probably refractory to aflatoxin carcinogenesis, but the early epidemiological evidence indicated otherwise. That epidemiological evidence, however, contained flaws so that Working Groups of the International Agency for Research on Cancer (IARC) meeting in 1970, 1976, and 1982, although ignoring the biochemical evidence, did consider the available epidemiological evidence insufficient for a conclusion of human carcinogenicity. During the 1970s and 1980s, studies on the connection between chronic infection with hepatitis B virus (HBV) and primary liver cell cancer (PLC), the expected lesion from aflatoxin exposure, had established a very strong etiological relationship between HBV and PLC. Since all the epidemiological studies of aflatoxin and PLC conducted prior to 1982 had been of populations with endemic HBV infection, and, in addition to other flaws, had not been controlled for this confounding factor, there was a solid basis for their rejection. Most epidemiological studies in the 1980s of aflatoxin and PLC were either in the United States, where HBV-infected groups could be excluded from the study, or, when in areas of chronic HBV infection, attempts were made to include that factor. The study of U.S. populations showed no difference in mortality rates from PLC that could be attributed to aflatoxin exposure. The studies of populations with endemic HBV infection produced no convincing evidence to support a primary role for aflatoxin in the induction of human PLC, although an accessory role to HBV infection for aflatoxin could not be ruled out. However, the epidemiological studies of the HBV/PLC relation indicate that an accessory factor is not an essential condition, a conclusion supported by animal models and a laboratory study that specifically found no interaction between aflatoxin and a hepatitis virus in the duck, a species in which liver cancer can be induced by either agent. It was surprising that an IARC Working Group meeting in 1987 concluded, on the basis of much of this evidence that was available at that time, and citing other studies that appear to be irrelevant to the issue, that there was sufficient evidence to consider aflatoxin a probable human carcinogen.

Aflatoxins↗

PubMed1992

P300, probability, and introverted/extroverted personality types.

Extreme introverted and extroverted subject groups (n = 24 each) containing equal numbers of male and females were assessed with the P300 (P3) component of the event-related potential (ERP). A two-tone auditory discrimination task in which the probability of the target stimulus varied systematically in different conditions (.20, .40, .60, .80) was used to elicit the ERPs. The P3 amplitude demonstrated a significant interaction between personality type, probability, and subject gender and was generally smaller for introverts than for extroverts. Female subjects tended to have larger overall P3 components than male subjects. P3 latency was not affected by the personality variable. The results support previous findings for ERP differences between introverts and extroverts and suggest that personality type differentially influences target stimulus probability effects. The findings are discussed in terms of individual differences in cortical activity on P3 amplitude and personality measures.

Adult↗

PubMed1992

Normal tissue complication probabilities: variable dose per fraction.

Because of the large amount of data generated by 3D treatment planning, new tools are being developed for the evaluation and optimization of the plans. Estimates of the probability of local control of the tumor and for the probability of specific normal tissue complications are among the new tools. The normal tissue complication probability (NTCP) is based on clinical estimates of the tolerance doses for specific tissues/organs. These tolerance doses are assumed to apply for uniform partial and full volume irradiations delivered at 2 Gy per fraction and 5 fractions per week. A different tolerance dose may apply when the dose is delivered at a different dose per fraction and over a different period of time. This study evaluates the maximum change expected in the NTCP when the normal structure receives the dose at a different dose per fraction than the target volume due to different choices in the delivery of the daily fraction.

Humans↗

PubMed1991

Outcome probabilities and life history after surgical mitral commissurotomy: implications for balloon commissurotomy.

From 1967 to 1988, 339 patients with mitral stenosis underwent surgical commissurotomy, 103 with a closed and 236 with an open technique. The 1 month and 1, 5, 10 and 20 year overall survival rate was 99.7%, 99%, 95%, 87% and 59%, respectively, and the technique (open versus closed) was not a risk factor. Technique was also not a risk factor for a second mitral commissurotomy, subsequent mitral valve replacement, thromboembolism or poor functional status. Risk factors were older age at commissurotomy, black race, higher pulmonary vascular resistance, mitral leaflet calcification, left ventricular enlargement and postcommissurotomy mitral incompetence. The closed technique was a risk factor for mitral incompetence immediately after commissurotomy, but important incompetence developed in only 2 of the 103 patients undergoing closed commissurotomy. Mitral valve replacement was not required within 10 years in 78% of patients and within 20 years in 47%. Despite some increased prevalence of postcommissurotomy mitral incompetence and particularly in view of the considerable long-term likelihood of mitral valve replacement, initial therapy for most patients with mitral stenosis should probably be surgical closed (or percutaneous balloon) mitral commissurotomy. The equations developed in the present study can be used to predict and compare outcome probability after percutaneous balloon commissurotomy with that after surgical commissurotomy and to compare these with outcome probability after mitral valve replacement.

Catheterization↗

PubMed2005

Individual cyclists' probability distributions of severe/fatal crashes in large French urban areas.

The present article deals with individual cyclists' probabilities of severe injury or death from a bicycle accident. We use an empirical Bayesian method to conduct an analysis of the fatal/severe probability distribution of a bicycle accident, at the level of individuals, in dense French urban areas. Among intuitive results, it is found that wearing a helmet lowers the average probability of such a crash; it is also shown that young bicyclists are, on average, more exposed to severe and/or fatal crashes. Finally, the results highlight a decrease of attention paid by all types of road users following road infrastructure improvements in favor of cyclists.

Accidents, Traffic↗

PubMed2005

MR imaging in probably benign lesions (BI-RADS category 3) of the breast.

PURPOSE: To investigate the role of dynamic magnetic resonance (MR) imaging in the evaluation of probably benign lesions (BI-RADS category 3) and its contribution to patient management. MATERIALS AND METHODS: Dynamic breast MR imaging was performed in 56 lesions assessed as probably benign in mammography of 43 patients. In MR imaging, T2-weighted turbo spin echo (TSE) with fat suppression sequence followed by pre- and post-contrast T1-weighted 3D-FLASH sequences were used. MR imaging findings were scored using 0-2 point criterion scale. The lesions were divided into five groups according to their total score (0 point: group 1, negative; 1-2 points: group 2, benign; 3 points: group 3, probably benign; 4-5 points: group 4, suspicious for malignancy; 6-8 points: group 5, highly suggestive of malignancy). Histopathologic verification of lesions in group 4 and above was obtained. Lesions in group 3 were either biopsied or followed up by mammography or MR imaging. Lesions in group 1-2 were followed by mammography of 6-month intervals for 2 years. The sensitivity, specificity, accuracy, and positive and negative predictive values of MR imaging in the determination of malignancy in BI-RADS category 3 lesions were calculated. RESULTS: Fifty-six findings (45 mass, 9 breast tissue, 2 focal enhancement) in 43 patients were detected in MR imaging. According to their total score, 41 lesions (73.2%) and breast tissue had 0 point (group 1); 10 lesions (17.8%) had 1-2 points (group 2); 2 lesions (3.6%) had 3 points (group 3); 2 lesions (3.6%) had 4 and 5 points (group 4); and 1 lesion (1.8%) had 6 points (group 5). Ten lesions (of six in groups 1 and 2, one in group 3, three in groups 4 and 5) were histopathologically confirmed. Out of 10 lesions, only 1 (1.8%) with 4 points in group 4 was diagnosed as invasive ductal carcinoma. Other lesions followed with mammography or MR imaging did not change. The sensitivity, specificity, accuracy, positive and negative predictive values of MR imaging in the determination of malignancy in BI-RADS category 3 lesions were calculated as 100, 96.4, 96.4, 33.3, and 100%, respectively. CONCLUSION: In the evaluation of BI-RADS category 3 lesions, dynamic MR imaging does not provide additional information with low positive predictive value similar to that of short interval mammography follow-up.

Breast↗

PubMed2005

Development and internal validation of a nomogram predicting the probability of prostate cancer Gleason sum upgrading between biopsy and radical prostatectomy pathology.

OBJECTIVE: Previous reports indicate that as many as 43% of men with low grade PCa at biopsy will be diagnosed with high-grade PCa at RP. We explored the rate of upgrading from biopsy to RP specimen in our contemporary cohort, and developed a model capable of predicting the probability of biopsy Gleason sum upgrading. MATERIALS AND METHODS: The study cohort consisted of 2982 men treated with RP, with available clinical stage, serum prostate specific antigen and biopsy Gleason scores. These clinical data were used as predictors in multivariate logistic regression models (LRM) addressing the rate of Gleason sum upgrading between biopsy and RP pathology. LRM regression coefficients were used to develop a nomogram predicting the probability of Gleason sum upgrading and was subjected to 200 bootstrap resamples for internal validation and to reduce overfit bias. RESULTS: Overall, 875 patients were upgraded (29.3%). In multivariate LRMs, all predictors were highly significant (all p values <0.0001). Bootstrap-corrected predictive accuracy of the nomogram predicting the probability of Gleason sum upgrading between biopsy and RP was 0.804. CONCLUSION: We developed a highly accurate clinical aid for treatment decision-making. It may prove useful when the possibility of a more aggressive Gleason variant may change the treatment options.

Biopsy↗

PubMed2005

Prospective evaluation of a screening protocol to exclude deep vein thrombosis on the basis of a combination of quantitative D-dimer testing and pretest clinical probability score.

BACKGROUND: Clinical signs and symptoms such as swelling, pain, and redness are unreliable markers of deep vein thrombosis (DVT). Because of this venous duplex scanning (VDS) has been heavily used in DVT detection. The purpose of this study was to determine if a combination of D-dimer testing and pretest clinical score could reduce the use of VDS in symptomatic patients with suspected DVT. STUDY DESIGN: One hundred seventy-four consecutive patients with suspected DVT were prospectively evaluated using pretest clinical probability (PCP) score and D-dimer testing before VDS. After calculating clinical probability scores developed by Wells and associates, patients were divided into low risk ( or=3 points) PCP. RESULTS: One hundred fifty-eight patients were enrolled. The prevalence of DVT in this study was 37%. Thirty-eight patients (24%) were classified as low risk, 64 (41%) as moderate risk, and 56 (35%) as high risk PCP. DVT was identified in only one patient (2.6%) with low risk PCP. In contrast, DVT was found in 22 (34%) with moderate risk, and 35 (63%) with high risk PCP. In the high and moderate risk PCP groups, positive scan patients had a markedly higher value of D-dimer assay than negative scan patients (p=0.0001 and p=0.0057, respectively). In the low risk PCP patients, D-dimer testing provided 100% sensitivity, 46% specificity, 4.8% positive predictive value, and 100% negative predictive value in the diagnosis of DVT. Similarly, in the moderate risk PCP, the D-dimer testing showed 100% sensitivity, 45% specificity, 49% positive predictive value, and 100% negative predictive value. In the high risk group, D-dimer testing achieved 100% sensitivity, 57% specificity, 80% positive predictive value, and 100% negative predictive value in the diagnosis of DVT. These results suggested that 36 of 158 patients who had a non-high PCP (low and moderate PCP) and a normal D-dimer concentration were considered to have no additional investigation, so VDS could have been reduced by 23% (36/158). CONCLUSIONS: A combination of D-dimer testing and clinical probability score may be effective in avoiding unnecessary VDS in suspected symptomatic DVT in the low and moderate PCP patients. The need for VDS could be reduced by 23% despite a relatively high prevalence of DVT.

Adult↗

PubMed2004

A simplified model for the assessment of the impact probability of fragments.

A model was developed for the assessment of fragment impact probability on a target vessel, following the collapse and fragmentation of a primary vessel due to internal pressure. The model provides the probability of impact of a fragment with defined shape, mass and initial velocity on a target of a known shape and at a given position with respect to the source point. The model is based on the ballistic analysis of the fragment trajectory and on the determination of impact probabilities by the analysis of initial direction of fragment flight. The model was validated using available literature data.

Accidents, Occupational↗

PubMed2003

Estimation of nonuniform quantal parameters with multiple-probability fluctuation analysis: theory, application and limitations.

Synapses are a key determinant of information processing in the central nervous system. Investigation of the mechanisms underlying synaptic transmission at central synapses is complicated by the inaccessibility of synaptic contacts and the fact that their temporal dynamics are governed by multiple parameters. Multiple-probability fluctuation analysis (MPFA) is a recently developed method for estimating quantal parameters from the variance and mean amplitude of evoked steady-state synaptic responses recorded under a range of release probability conditions. This article describes the theoretical basis and the underlying assumptions of MPFA, illustrating how a simplified multinomial model can be used to estimate mean quantal parameters at synapses where quantal size and release probability are nonuniform. Interpretations of the quantal parameter estimates are discussed in relation to uniquantal and multiquantal models of transmission. Practical aspects of this method are illustrated including a new method for estimating quantal size and variability, approaches for optimising data collection, error analysis and a method for identifying multivesicular release. The advantages and limitations of investigating synaptic function with MPFA are explored and contrasted with those for traditional quantal analysis and more recent optical quantal analysis methods.

Algorithms↗

PubMed2006

Robot-assisted hindlimb extension increases the probability of swing initiation during treadmill walking by spinal cord contused rats.

Training and evaluation of locomotion in animals with spinal cord injury will likely be improved with the development of techniques that increase stepping activity. We hypothesized that robot-assisted extension of the hindlimbs of spinal cord injured rats during stance would increase the probability that the swing phase of gait would be initiated. Thirty-three adult, Sprague-Dawley rats received a contusion injury to the mid-thoracic spinal cord. The animals' hindlimbs were pulled into extension using small robotic arms to pull at the ankle, as the rat stepped on either a reciprocating, robotic paw platform or a conventional treadmill belt. The animals demonstrated an increase in the probability of swing initiation with spontaneous recovery during the first 4 weeks following injury (p < 0.0001). The probability of swing initiation was found to be greater with the use of robot-assisted extension versus no extension force at the ankle (75+/-16.9% versus 38.9+/-16.6%, p < 0.001). Swing initiation occurred most frequently at a particular distance of hindlimb extension (50 mm caudal from the neutral position at stance), but was broadly tuned about this distance. These results indicate that a greater amount of stepping activity can be elicited by robot-assisted extension, thereby providing possible benefits to evaluation and training of gait following SCI.

Algorithms↗

PubMed2006

Characterization of bacterial isolates from industrial wastewater according to probable modes of hexadecane uptake.

Bacterial isolates from industrial wastewater were characterized according to probable modes of hexadecane uptake based on data for cell surface hydrophobicity, emulsifying activity, glycoside content and surface tension of cell-free culture medium. The results obtained suggested that both modes of biosurfactant-enhanced hexadecane uptake by bacterial strains take place, direct uptake and alkane transfer. The increase in cell surface hydrophobicity and glycoside production by the strains suggested the existence of biosurfactant-enhanced interfacial uptake of the alkane. Such mechanism is probably predominant for three isolates, Staphylococcus sp. HW-2, Streptococcus sp. HW-9 and Bacillus sp. HW-4. Secreted biosurfactants enhanced mainly alkane emulsification for most hydrophobic isolate Arthrobacter sp. HW-8, and micellar transfer for most hydrophilic isolate Streptococcus sp. HW-5. For other strains (67%) both mechanisms of biosurfactant-enhanced hexadecane uptake probably take place in similar degree, interfacial uptake and alkane emulsification. The results obtained could contribute to clarifying the natural relationships between the members of water ecosystem studied as well as will reveal potential producers of surface active compounds.

Alkanes↗

PubMed2005

[Diagnostic value of the clinical probability score of deep venous thrombosis in the elderly].

SUBJECT: There is a lack of scientific data concerning the incidence, clinical signs, risk factors and diagnostic management of deep vein thrombosis (DVT) in the elderly. METHODS: We carried out a prospective case-control study in a geriatric setting. We included one in-patient without clinical signs of deep vein thrombosis for each hospitalised patient with clinically suspected DVT. Clinical signs, risk factors of DVT and a compression ultrasonography of the proximal and distal leg veins were performed in all patients at admission. Also, the clinical probability was assessed by means of the clinical score model described by Wells. RESULTS: There were 102 patients aged over 85 included during the 5 months period of the study. Fifty-one patients have had a clinical suspicion of DVT and 51 patients were clinically asymptomatic. There were 43% symptomatic DVT and 12% asymptomatic DVT. Clinical signs and symptoms of DVT were neither sensitive nor specific. Risk factors associated most frequently with DVT were: immobilisation (prevalence 64%), paralysis of the legs (22%), varicose veins (25%), deshydratation (28,5%), infections (18%). A significant relationship between a risk factor and DVT was found only for immobilisation (P<0,05) and deshydratation (P<0,02). The prevalence of DVT increased with the clinical probability score: 11.4% for the low score, 27.6% for the moderate score and 55% for the high score. CONCLUSION: Incidence of DVT is high among hospitalised elderly patients, especially for the asymptomatic ones. Clinical signs alone do not reliably predict DVT. Clinical probability score could be useful to improve diagnostic management of DVT in this population.

Aged↗