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PubMed1981

The probability of fetal metabolic acidosis during labor in a population at risk as determined by clinical factors.

The clinical data derived from 2,772 pregnancies managed in an intrapartum intensive care unit have been analyzed to establish which criteria will indicate in a more definite manner the probability that fetal metabolic acidosis will occur during labor and delivery. All antepartum and intrapartum clinical factors indicate a pregnancy and fetus with an increased probability of fetal metabolic acidosis. However, there is a remarkably consistent relationship between decreasing fetal weight in each week of gestational age and in increasing probability of fetal metabolic acidosis that will permit the magnitude of the risk to be determined with greater precision. The following clinical guidelines are proposed: (1) Current antepartum and intrapartum risk factors are appropriate for the selection of patients for intrapartum intensive care. (2) An accurate gestational age and an estimate of fetal weight within 200 gm will provide an indication of the probability of fetal metabolic acidosis in the individual fetus ranging from 15% to 50%. (3) The presence of meconium in the amniotic fluid increases the probability of metabolic acidosis as defined by fetal weight in relation to gestational age.

Acidosis↗

PubMed2001

Probability of Nd:YAG laser capsulotomy after cataract surgery in Olmsted County, Minnesota.

PURPOSE: To estimate the cumulative probability of Nd:YAG laser posterior capsulotomy after cataract extraction in a geographically defined population. METHODS: Rochester Epidemiology Project databases were used to identify retrospectively all Nd:YAG laser posterior capsulotomies performed on Olmsted County, Minnesota, residents who had previously undergone cataract extraction between 1988 and 1996, inclusive. Demographic data and potential risk factors for laser, including age, sex, surgical technique, year of surgery, and intraocular lens material, were obtained by chart review or by retrieval from computer databases. The cumulative probability of Nd:YAG laser posterior capsulotomy was calculated by Kaplan-Meier estimates, and risk factors were analyzed using the Cox proportional hazards model. RESULTS: A total of 925 Nd:YAG laser posterior capsulotomies were identified after 3541 cataract extractions in 2718 patients. The cumulative probability of Nd:YAG laser posterior capsulotomy after cataract surgery was 6% (95% confidence interval = 5% to 7%) at 1 year, increasing to 38% (35% to 40%) at 9 years. Young age at the time of surgery (P =.02), polymethylmethacrylate intraocular lens material (P <.001), earlier year of surgery (P <.001), and extracapsular extraction (in comparison with phacoemulsification, P <.001) were found to increase significantly the risk of subsequent Nd:YAG laser posterior capsulotomy. Women tended to have a greater probability of Nd:YAG laser posterior capsulotomy (P =.17), but this difference was not statistically significant. CONCLUSIONS: Nd:YAG laser posterior capsulotomy was common after cataract surgery but infrequent during the first postoperative year. Prolonged follow-up is necessary in investigations of the effects of new cataract surgery technologies on the probability of capsulotomy.

Adolescent↗

PubMed1994

Premelting base pair opening probability and drug binding constant of a daunomycin-poly d(GCAT).poly d(ATGC) complex.

We calculate room temperature thermal fluctuational base pair opening probability of a daunomycin-poly d(GCAT).poly d(ATGC) complex. This system is constructed at an atomic level of detail based on x-ray analysis of a crystal structure. The base pair opening probabilities are calculated from a modified self-consistent phonon approach of anharmonic lattice dynamics theory. We find that daunomycin binding substantially enhances the thermal stability of one of the base pairs adjacent the drug because of strong hydrogen bonding between the drug and the base. The possible effect of this enhanced stability on the drug inhibition of DNA transcription and replication is discussed. We also calculate the probability of drug dissociation from the helix based on the selfconsistent calculation of the probability of the disruption of drug-base H-bonds and the unstacking probability of the drug. The calculations can be used to determine the equilibrium drug binding constant which is found to be in good agreement with observations on similar daunomycin-DNA systems.

Base Composition↗

PubMed2003

Surprises: low probabilities or high contrasts?

Outcome expectations can be expressed prospectively in terms of probability estimates, and retrospectively in terms of surprise. Surprise ratings and probability estimates differ, however, in some important ways. Surprises are generally created by low-probability outcomes, yet, as shown by several experiments, not all low-probability outcomes are equally surprising. To account for surprise, we propose a contrast hypothesis according to which the level of surprise associated with an outcome is mainly determined by the extent to which it contrasts with the default, expected alternative. Three ways by which contrasts can be established are explored: contrasts due to relative probabilities, where the obtained outcome is less likely than a default alternative; contrasts formed by novelty and change, where a contrast exists between the obtained outcome and the individual's previous experience; and contrasts due to the perceptual or conceptual distance between the expected and the obtained. In all these cases, greater contrast was accompanied by higher ratings of surprise.

Affect↗

PubMed1995

Familial sinistrality: the utility of calculating exact genotype probabilities for individuals.

Measures of familial sinistrality are frequently used in neuropsychological research. However they suffer from the problem that they are essentially a global measure of phenotypes in the family, whereas they are interpreted as an indicator of the genotype of the individual concerned. In this paper it is shown how to calculate a precise probabilistic estimate of a proband's genotype, given a particular genetic model of handedness, using all of the information available in a family tree. Example calculations are provided for a range of families with one or two sinistral relatives. Genotype probabilities are also calculated for a large population data set (the National Childhood Encephalopathy Study) and it is shown that familial sinistrality does not account for all of the variability present in the genotype probabilities, and that genotype probabilities provide an additional prediction of individual sinistrality after taking familial sinistrality into account, whereas all of the information in familial sinistrality is accounted for by the genotype probabilities. Finally it is shown how genotype probabilities can be used to assess whether there is heterozygote advantage for a characteristic, and using this method it is suggested that there is no support for heterozygotes having higher intellectual ability than homozygotes.

Family↗

PubMed2003

Vulvar mucus observations and the probability of pregnancy.

OBJECTIVE: To assess the day-specific and cycle-specific probabilities of conception leading to clinical pregnancy, in relation to the timing of intercourse and vulvar mucus observations. METHODS: This was a retrospective cohort study of women beginning use of the Creighton Model Fertility Care System in Missouri, Nebraska, Kansas, and California. Data were abstracted from Creighton Model Fertility Care System records, including women's daily standardized vulvar observations of cervical mucus discharge, days of intercourse, and clinically evident pregnancy (conception). Established statistical models were used to estimate day-specific probabilities of conception. RESULTS: Data were analyzed from 1681 cycles with 81 conceptions from 309 normally fertile couples (initially seeking to avoid pregnancy) and from 373 cycles with 30 conceptions from 117 subfertile couples (who were initially trying to achieve pregnancy). The highest probability of pregnancy occurred on the peak day of vulvar mucus observation (.38 for normally fertile couples and.14 for subfertile couples). The probability of pregnancy was greater than.05 for normally fertile couples from 3 days before to 2 days after the peak, and for subfertile couples from 1 day before to 1 day after the peak. The cycle-specific probability of conception correlated with the quality of mucus discharge in normally fertile couples but not in subfertile couples. CONCLUSION: Standardized vulvar observations of vaginal mucus discharge identify the days with the greatest likelihood of conception from intercourse in normal fertility and subfertility and provide an indicator of the overall potential for conception in a given menstrual cycle in normal fertility.

Cervix Mucus↗

PubMed2001

Field size reduction enables iso-NTCP escalation of tumor control probability for irradiation of lung tumors.

PURPOSE: With the mean lung dose (MLD) as an estimator for the normal tissue complication probability (NTCP) of the lung, we assessed whether the probability of tumor control of lung tumors might be increased by dose escalation in combination with a reduction of field sizes, thus increasing target dose inhomogeneity while maintaining a constant MLD. METHODS AND MATERIALS: An 8-MV AP-PA irradiation of a lung tumor, located in a cylindrically symmetric lung-equivalent phantom, was modeled using numerical simulation. Movement of the clinical target volume (CTV) due to patient breathing and setup errors was simulated. The probability of tumor control, expressed as the equivalent uniform dose (EUD) of the CTV, was assessed as a function of field size, under the constraint of a constant MLD. The approach was tested for a treatment of a non-small cell lung cancer (NSCLC) patient using the beam directions of the clinically applied treatment plan. RESULTS: In the phantom simulation it was shown that by choosing field sizes that ensured a minimum dose of 95% in the CTV ("conventional" plan) taking into account setup errors and tumor motion, an EUD of the CTV of 43.8 Gy can be obtained for a prescribed dose of 44.2 Gy. By reducing the field size and thus shifting the 95% isodose surface inwards, the EUD increases to a maximum of 68.3 Gy with a minimum dose in the CTV of 55.2 Gy. This increase in EUD is caused by the fact that field size reduction enables escalation of the prescribed dose while maintaining a constant MLD. Further reduction of the field size results in decrease of the EUD because the minimum dose in the CTV becomes so low that it has a predominant effect on the EUD, despite further escalation of the prescribed dose. For the NSCLC patient, the EUD could be increased from an initial 62.2 Gy for the conventional plan, to 83.2 Gy at maximum. In this maximum, the prescribed dose is 88.1 Gy, and the minimum dose in the CTV is 67.4 Gy. In this case, the 95% isodose surface is conformed closely to the "static" CTV during treatment planning. CONCLUSIONS: Iso-NTCP escalation of the probability of tumor control is possible for lung tumors by reducing field sizes and allowing a larger dose inhomogeneity in the CTV. Optimum field sizes can be derived, having the highest EUD and highest minimum dose in the CTV under condition of a constant NTCP of the lungs. We conclude that the concept of homogeneous dose in the target volume is not the best approach to reach the highest probability of tumor control for lung tumors.

Humans↗

PubMed2002

Margins for translational and rotational uncertainties: a probability-based approach.

PURPOSE: To define margins for systematic rotations and translations, based on known statistical distributions of these deviations. METHODS AND MATERIALS: The confidence interval-based expansion method for translations, known as the "rolling ball algorithm," was extended to include rotations. This new method, which we call the Rotational and Translational Confidence Limit (RTCL) method, is exact for a point with arbitrary rotations and translations or for a finite shape with rotations only. The method was compared with two existing expansion methods: a rolling ball algorithm without rotations, and a convolution (blurring) method which included rotations. On the basis of these methods, planning target volumes (PTVs, expanded clinical target volumes [CTVs]) were constructed for a number of shapes (a sphere, a sphere with an extension, and three prostate cases), and evaluated in several ways by means of a Monte Carlo method. The accuracy of each method was measured by determining the probability of finding the CTV completely inside the PTV (P(CTVinPTV)), using parameters that yield a 90% probability for a sphere-shaped CTV without rotations. Furthermore, with the expansion parameters adjusted to give an equal P(CTVinPTV) for all methods, PTV volumes were compared. RESULTS: With the expansion algorithm parameters chosen to yield P(CTVinPTV) = 90% for a sphere, an average P(CTVinPTV) of 84%, 57%, and 46% was obtained for the other shapes, using the RTCL method, coverage probability, and rolling ball, respectively. With the parameters adjusted to yield an equal P(CTVinPTV) for all methods, the PTV volume was on average 8% larger for the coverage probability method and 15% larger for the rolling ball algorithm compared to the RTCL method. CONCLUSION: The RTCL method provides an accurate way to include the effects of systematic rotations in the margin. Compared to other algorithms, the method is less sensitive to the shape of the CTV, and, given a fixed probability of finding the CTV inside the PTV, a smaller PTV volume can be obtained.

Algorithms↗

PubMed2004

Probability and cost estimates for social and physical outcomes in social phobia and panic disorder.

Individuals with Social Phobia (SP) (n = 23) and Panic Disorder (n = 22), and a non-anxious comparison (NAC) group (n = 62) rated the probability and cost of negative outcomes in the physical and the social domains. Overall, participants rated physical events as less probable but more costly than social events. Compared to the non-anxious group, participants with Social Phobia made significantly higher probability and cost estimates for social events, but not for physical events. Multiple regression analyses demonstrated that perceived cost of negative social events was the strongest unique predictor of scores on the Fear of Negative Evaluation Scale (FNE). Participants with Panic Disorder made significantly higher probability and cost estimates for both physical and social outcomes, compared to non-anxious participants. Both physical probability and social cost estimates predicted scores on the Body Sensations Questionnaire (BSQ). Findings support the disorder-specificity of cognitive biases in Social Phobia, but suggest that individuals with Panic Disorder have a wider range of judgment biases than previously thought.

Adult↗

PubMed2003

Probability effects on event-related potential correlates of recognition memory.

A common finding in event-related potential (ERP) studies of recognition memory is that recognised items elicit greater positivity at parietal electrode sites than new items (the 'left parietal old/new effect'). Parietal positivity (the P300 or P3b) is also elicited in detection tasks with no memory demands by items of low probability of occurrence and high 'target value'. It has been argued that correctly recognised items are typically associated with lower probability and higher target value than new items, raising the question of the extent to which the old/new effect receives a contribution from, or interacts with, P300 activity. The present study explored this issue by comparing ERPs associated with correctly classified old and new items across three different ratios of old to new items: 25:75, 50:50 and 75:25. The left parietal old/new effect was not influenced by this manipulation in the latency range in which it is conventionally measured. Probability did influence the parietal ERPs to correctly recognised items post-800 ms; the scalp distribution of this probability effect was however qualitatively distinct from that of the preceding old/new effect. The left parietal old/new effect appears to be a relatively pure reflection of episodic retrieval, uncontaminated by the non-mnemonic factors of probability and target value.

Adolescent↗

PubMed2003

Posterior probability maps and SPMs.

This technical note describes the construction of posterior probability maps that enable conditional or Bayesian inferences about regionally specific effects in neuroimaging. Posterior probability maps are images of the probability or confidence that an activation exceeds some specified threshold, given the data. Posterior probability maps (PPMs) represent a complementary alternative to statistical parametric maps (SPMs) that are used to make classical inferences. However, a key problem in Bayesian inference is the specification of appropriate priors. This problem can be finessed using empirical Bayes in which prior variances are estimated from the data, under some simple assumptions about their form. Empirical Bayes requires a hierarchical observation model, in which higher levels can be regarded as providing prior constraints on lower levels. In neuroimaging, observations of the same effect over voxels provide a natural, two-level hierarchy that enables an empirical Bayesian approach. In this note we present a brief motivation and the operational details of a simple empirical Bayesian method for computing posterior probability maps. We then compare Bayesian and classical inference through the equivalent PPMs and SPMs testing for the same effect in the same data.

Algorithms↗

PubMed2004

Power calculations for the transmission/disequilibrium and affected sib pair tests using elementary probability methods.

The transmission/disequilibrium test (TDT) and the affected sib pair test (ASP) both test for the association of a marker allele with some conditions. Here, we present methods for calculating the probability of detecting the association (power) for a study examining a fixed number of families for suitability for the study and for calculating the number of such families to be examined. Both calculations use a genetic model for the association. The model considered posits a bi-allelic marker locus that is linked to a bi-allelic disease locus with a possibly nonzero recombination fraction between the loci. The penetrance of the disease is an increasing function of the number of disease alleles. The TDT tests whether the transmission by a heterozygous parent of a particular allele at a marker locus to an affected offspring occurs with probability greater than 0.5. The ASP tests whether transmission of the same allele to two affected sibs occurs with probability greater than 0.5. In either case, evidence that the probability is greater than 0.5 is evidence for association between the marker and the disease. Study inclusion criteria (IC) can greatly affect the necessary sample size of a TDT or ASP study. IC considered by us include a randomly selected parent at least one parent or both parents required to be heterozygous. It also allows a specified minimum number of affected offspring to be required (TDT only). We use elementary probability calculations rather than complex mathematical manipulations or asymptotic methods (large sample size approximations) to compute power and requisite sample size for a proposed study. The advantages of these methods are simplicity and generality.

Chromosome Mapping↗

PubMedDate not supplied

Statistical mechanical treatment of protein conformation. 6. Elimination of empirical rules for prediction by use of a high-order probability. Correlation between the amino acid sequences and conformations for homologous neurotoxin proteins.

One-dimensional short-range interaction models for specific-sequence copolymers of amino acids have been developed in this series of papers. In this paper, a general method for predicting protein conformation (that is based on a one-dimensional short-range interaction model, and eliminates the need for the empirical rules introduced in papers III and IV) is described. The present method involves the use of conformational (or conformational-sequence) probabilities of higher order than the first- or second-order probabilities used in papers IV and V, i.e., it treats a sequence of any number of residues; it thus alters the predictive methods that involved empirical rules in papers III and IV, and low-order (first- or second-order) probabilities in papers IV and V. The general method is applied here to the prediction of the backbone conformations of proteins, using the three-state model [helical (h), extended (epilson), and other coil (c) states] proposed in the theoretical formulation of paper II. The statistical weights in the three-state model are evaluated from the atomic coordinates of the x-ray structures of 26 proteins. The conformational-sequence probabilities (taken for three consecutive residues for numerical computation in this paper) are calculated for all possible triads (i.e., for all possible combinations of the three states, h, epilson, and c for each residue) for bovine pancreatic trypsin inhibitor and clostridial flavodoxin, in order to select the most probable conformations of these proteins. The predicted results for these proteins are compared to those predicted in paper III and to those observed experimentally. The method is applied further to the prediction of the backbone structures of homologous neurotoxin proteins whose amino acid sequences are known but whose x-ray structures are not. The effects of variation in the amino acid sequence on the conformations of the backbones are discussed from the point of view of the homologies in the amino acid sequences of 19 neurotoxins. Application of the present general predictive method to a four- and a multistate model is also described.

Amino Acid Sequence↗

PubMed1997

Effects of subpopulation structure on probability calculations of DNA profiles from forensic PCR analysis.

DNA typing for forensic identification is a two-step process. The first step involves determining the profiles of samples collected at the crime scene and comparing them with the profiles obtained from suspects and the victims. In the case of a match that includes the suspect as the potential source of the material collected at the crime scene, the last step in the process is to answer the question, what is the likelihood that someone in addition to the suspect could match the profile of the sample studied? This likelihood is calculated by determining the frequency of the suspect's profile in the relevant population databases. The design of forensic databases and the criteria for comparison has been addressed by the NRC report of 1996 (National Research Council, 1996). However, the fact that geographical proximity, migrational patterns, and even cultural and social practices have effects on subpopulation structure establishes the grounds for further study into its effects on the calculation of probability of occurrence values. The issue becomes more relevant in the case of discrete polymorphic markers that show higher probability of occurrence in the reference populations, where several orders of magnitude difference between the databases may have an impact on the jury. In this study, we calculated G values for all possible pairwise comparisons of allelic frequencies in the different databases from the races or subpopulations examined. In addition, we analyzed a set of 24 unrelated Caucasian, 37 unrelated African-American, and 96 unrelated Sioux/Chippewa individuals for seven polymorphic loci (DQA1, LDLR, GYPA, HBGG, D7S8, GC, and D1S80). All three sets of individuals where sampled from Minnesota. The probability of occurrence for all seven loci were calculated with respect to nine different databases: Caucasian, Arabic, Korean, Sioux/Chippewa, Navajo, Pueblo, African American, Southeastern Hispanic, and Southwestern Hispanic. Analysis of the results demonstrated marked differences in the probabilities of occurrence when individuals were compared to the different populations and subpopulation databases. The possible genetic and forensic consequences of subpopulation structure on probability calculations are discussed.

DNA Fingerprinting↗

PubMed2002

Loci of signal probability effects and of the attentional blink bottleneck.

To investigate the locus of signal probability effects and the influence of stimulus quality on this locus, the authors manipulated probability in Task 2 of a psychological refractory period (PRP) paradigm. The effect was additive with stimulus onset asynchrony (SOA) when the target was not masked but underadditive with decreasing SOA when the target was masked. Even with masking, however, a range of probabilities had effects additive with SOA. The results suggest loci of stimulus probability before the PRP bottleneck as well as at or after the bottleneck. A second issue addressed was the locus of interference in the attentional blink (AB). The AB was larger when the probability of the first of 2 targets was lower. The results lead to the conclusion that one cause of the AB effect is a locus at least as late as the PRP bottleneck.

Attention↗

PubMed2004

Sublexical and lexical representations in speech production: effects of phonotactic probability and onset density.

Phonotactic probability, neighborhood density, and onset density were manipulated in 4 picture-naming tasks. Experiment 1 showed that pictures of words with high phonotactic probability were named more quickly than pictures of words with low phonotactic probability. This effect was consistent over multiple presentations of the pictures (Experiment 2). Manipulations of phonotactic probability and neighborhood density showed only an influence of phonotactic probability (Experiment 3). In Experiment 4, pictures of words with sparse onsets were named more quickly than pictures of words with dense onsets. The results of these experiments provide additional constraints on the architecture and processes involved in models of speech production, as well as constraints on the connections between the recognition and production systems.

Attention↗

PubMed2004

Typical versus atypical unpacking and superadditive probability judgment.

Probability judgments for packed descriptions of events (e.g., the probability that a businessman does business with a European country) are compared with judgments for unpacked descriptions of the same events (e.g., the probability that a businessman does business with England, France, or some other European country). The prediction that unpacking can decrease probability judgments, derived from the hypothesis that category descriptions are interpreted narrowly in terms of typical instances, is contrasted to the prediction of support theory that unpacking will generally increase judged probabilities (A. Tversky & D. J. Koehler, 1994). The authors varied the typicality of unpacked instances and found no effect of unpacking with typical instances (additivity) and a negative effect with atypical instances (superadditivity). Support theory cannot account for these findings in its current formulation.

Humans↗

PubMed2002

Probability of adult overweight and risk change during the BMI rebound period.

OBJECTIVE: To develop a probability chart of adult overweight based on childhood body mass index (BMI) values and to evaluate the BMI change during the BMI rebound period during childhood, in different populations, with the use of risk function curves. RESEARCH METHODS AND PROCEDURES: A longitudinal growth study of 3650 full-term healthy Swedish children followed from birth to 18 years of age. Weight and height values of our subjects were obtained. RESULTS: A probability chart for reaching a BMI > 23 kg/m(2) at 18 years of age was constructed for boys and girls. For example, a BMI of 18 kg/m(2) at 4 years of age is associated with 0.70 probability of attaining a BMI > 23 kg/m(2) at 18 years of age in boys; a BMI of 16 kg/m(2) at 4 years of age leads to 0.40 probability of having a BMI > 23 kg/m(2) at 18 years of age in girls. Children with an obvious BMI rebound before 8 years of age have a high risk of being overweight at 18 years of age. There is a clear trend of BMI increase from the 1970s to the 1990s in U.S. children from a parallel dataset, and Hispanic children are at the highest risk of adult overweight. DISCUSSION: The probability chart for adult overweight developed here provides a functional method of defining childhood obesity that is based on the risk of long-term ill health rather than on a certain statistical cut-off point. It will help pediatricians or healthcare workers identify those children who are at a high risk of becoming overweight in adulthood, which will allow clinical intervention at younger ages.

Adolescent↗