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PubMed1995

Applications of the Dirichlet distribution to forensic match probabilities.

The Dirichlet distribution provides a convenient conjugate prior for Bayesian analyses involving multinomial proportions. In particular, allele frequency estimation can be carried out with a Dirichlet prior. If data from several distinct populations are available, then the parameters characterizing the Dirichlet prior can be estimated by maximum likelihood and then used for allele frequency estimation in each of the separate populations. This empirical Bayes procedure tends to moderate extreme multinomial estimates based on sample proportions. The Dirichlet distribution can also be employed to model the contributions from different ancestral populations in computing forensic match probabilities. If the ancestral populations are in genetic equilibrium, then the product rule for computing match probabilities is valid conditional on the ancestral contributions to a typical person of the reference population. This fact facilitates computation of match probabilities and tight upper bounds to match probabilities.

Alleles↗

PubMed2005

Strategic modulation of the fixation-offset effect: dissociable effects of target probability on prosaccades and antisaccades.

In several previous experiments examining the effects of participants' expectations on oculomotor performance, the manipulation of target probability has been confounded with factors such as target occurrence and saccade frequency. We report results from three experiments that manipulated target probability in isolation from systematic variations in such bottom-up factors. We present evidence for trial-by-trial, top-down modulation of the fixation-offset effect in prosaccade latency. Furthermore, fixation-stimulus offset and target-probability manipulations had additive effects on antisaccade latency, suggesting that these factors influence separable neural processes engaged for antisaccade performance. Based on these findings, we suggest that cognitive processes utilizing target-probability information influence task processes engaged for prosaccades that differ from those engaged for antisaccades.

Adult↗

PubMed2003

A diagnostic strategy for pulmonary embolism based on standardised pretest probability and perfusion lung scanning: a management study.

Pulmonary embolism remains a challenging diagnostic problem. We developed a simple diagnostic strategy based on combination of assessment of the pretest probability with perfusion lung scan results to reduce the need for pulmonary angiography. We studied 390 consecutive patients (78% in-patients) with suspected pulmonary embolism. The pretest probability was rated low (<10%), intermediate (>10%, < or =50%), moderately high (>50%, < or =90%) or high (>90%) according to a structured clinical model. Perfusion lung scans were independently assigned to one of four categories: normal; near-normal; abnormal, suggestive of pulmonary embolism (wedge-shaped perfusion defects); abnormal, not suggestive of pulmonary embolism (perfusion defects other than wedge shaped). Pulmonary embolism was diagnosed in patients with abnormal scans suggestive of pulmonary embolism and moderately high or high pretest probability. Patients with normal or near-normal scans and those with abnormal scans not suggestive of pulmonary embolism and low pretest probability were deemed not to have pulmonary embolism. All other patients were allocated to pulmonary angiography. Patients in whom pulmonary embolism was excluded were left untreated. All patients were followed up for 1 year. Pulmonary embolism was diagnosed non-invasively in 132 patients (34%), and excluded in 191 (49%). Pulmonary angiography was required in 67 patients (17%). The prevalence of pulmonary embolism was 41% ( n=160). Patients in whom pulmonary embolism was excluded had a thrombo-embolic risk of 0.4% (95% confidence interval: 0.0%-2.8%). Our strategy permitted a non-invasive diagnosis or exclusion of pulmonary embolism in 83% of the cases (95% confidence interval: 79%-86%), and appeared to be safe.

Adolescent↗

PubMed2003

The probability of malignancy in small pulmonary nodules coexisting with potentially operable lung cancer detected by CT.

The aim of this study was to assess the probability of malignancy in one or two small nodules 1 cm or less coexisting with potentially operable lung cancer (coexisting small nodules). The preoperative helical CT scans of 223 patients with lung cancer were retrospectively reviewed. The probability of malignancy of coexisting small nodules was evaluated based on nodule size, location, and clinical stage of the primary lung cancers. Seventy-one coexisting small nodules were found on conventional CT in 58 (26%) of 223 patients, and 14 (6%) patients had malignant nodules. Eighteen (25%) of such nodules were malignant. The probability of malignancy was not significantly different between two groups of nodules larger and smaller than 0.5 cm ( p=0.1). The probability of malignancy of such nodules within primary tumor lobe was significantly higher than that in the other lobes ( p<0.01). Metastatic nodules were significantly fewer in clinical stage-IA patients than in the patients with the other stage ( p<0.01); however, four (57%) of seven synchronous lung cancers were located in the non-primary tumor lobes in the clinical stage-I patients. Malignant coexisting small nodules are not infrequent, and such nodules in the non-primary tumor lobes should be carefully diagnosed.

Adult↗

PubMed2001

Correlated hit probability and cell transformation in an effect-specific track length model applied to in vitro alpha irradiation.

In estimating the risk from low doses of alpha particles such as those emitted by radon progeny, it is important to consider the correlation between cellular inactivation and transformation that can exist at the cellular level. A phenomenological model of radiation-induced cellular inactivation and transformation at this level is presented here which incorporates aspects of a state vector model of radiation carcinogenesis and of correlated hit probabilities for inactivation and transformation. The general form of the model assumes that both inactivation and initial initiation damage are produced through the interaction of sublesions induced by radiation passing through cell nuclei, with the production of sublesions governed by hit probabilities and a characteristic probability-per-unit track length. The inactivation and initiation events are partially correlated through the use of hit probabilities. In addition, promotional events are incorporated for the case of cellular transformation based on a previously published state vector model. The model provides good fits to available data on the relationship between inactivation, transformation and LET for doses of alpha above 0.1 Gy in the range of LETs commonly produced by radon and progeny; by "good fits" we mean here the ability to yield the correct shapes of dose-response data using parameter values that vary smoothly with LET and using inactivation parameters that are applied consistently between inactivation and transformation assays. The resulting model correctly predicts recent findings indicating an increased transformation frequency per surviving cell when a population receives a distribution of hits compared to irradiation where all cells receive the same number of hits.

Animals↗

PubMed2005

A gene selection algorithm based on the gene regulation probability using maximal likelihood estimation.

A novel gene selection algorithm based on the gene regulation probability is proposed. In this algorithm, a probabilistic model is established to estimate gene regulation probabilities using the maximum likelihood estimation method and then these probabilities are used to select key genes related by class distinction. The application on the leukemia data-set suggests that the defined gene regulation probability can identify the key genes to the acute lymphoblastic leukemia (ALL)/acute myeloid leukemia (AML) class distinction and the result of our proposed algorithm is competitive to those of the previous algorithms.

Acute Disease↗

PubMed2006

Can we gain precision by sampling with probabilities proportional to size in surveying recent landscape changes in the Netherlands?

Seventy-two squares of 100 ha were selected by stratified random sampling with probabilities proportional to size (pps) to survey landscape changes in the period 1996-2003. The area of the plots times the urbanization pressure was used as a size measure. The central question of this study is whether the sampling with probabilities proportional to size leads to gain in precision compared to equal probability sampling. On average 1.03 isolated buildings per 100 ha have been built, while 0.90 buildings per 100 ha have been removed, leading to a net change of 0.13 building per 100 ha. The area with unspoiled natural relief has been reduced by 2.3 ha per 100 ha, and the length of linear relicts by 137 m per 100 ha. On average 74 m of linear green elements have been planted per 100 ha, while 106 m have been removed, leading to a net change of -31 m per 100 ha. For the state variables 'unspoiled natural relief', 'linear relicts', 'removed linear green elements', and 'new-removed linear green elements' there is a gain in precision due to the pps-sampling. For the remaining state variables there is no gain or even a loss of precision ('new buildings', 'removed buildings', 'new-removed buildings', 'new linear green elements'). Therefore, if many state variables must be monitored or when interest is not only in the change but also in the current totals, we recommend to keep things simple, and to select plots with equal probability.

Environmental Monitoring↗

PubMed2005

Alcohol's effects on video lottery terminal (VLT) play among probable pathological and non-pathological gamblers.

This study tested whether alcohol increases behaviors associated with video lottery terminal (VLT) play, particularly among probable pathological gamblers. Forty-four regular VLT players were designated either probable pathological gamblers or non-pathological gamblers on the basis of scores on the South Oaks Gambling Screen (SOGS); [Lesieur & Blume (1997). American Journal of Psychiatry, 144, 1184-1188] Gamblers from each SOGS category were randomly assigned to either a moderately intoxicating alcohol dose or a control beverage condition (n = 11 per cell in the 2 x 2 between-subjects design). Following beverage consumption and absorption, participants played a video poker VLT game for up to 30 minutes. Four behaviors were measured: "power-bets" (doubling bet after viewing only two cards of the five-card poker hand); total money spent; mean bet magnitude; and number of minutes played. Alcohol increased time spent playing and rate of power-bets, particular among the probable pathological gamblers. Post hoc analyses revealed that alcohol also influenced the proportion of losing hands played--increasing them among the probable pathological gamblers while decreasing them among the non-pathological gamblers. Clinical and policy implications of the findings are discussed.

Adult↗

PubMed1993

Quantitative analysis of the 'phosphocreatine shuttle': I. A probability approach to the description of phosphocreatine production in the coupled creatine kinase-ATP/ADP translocase-oxidative phosphorylation reactions in heart mitochondria.

For the first time, a probability approach was used to describe heart mitochondrial respiration in the medium with ATP, Cr and PCr but without ADP. Respiring mitochondria were considered as a three-component system, including (1) oxidative phosphorylation reactions which provide stable ATP concentration in the mitochondrial matrix; (2) adenine nucleotide translocase, which provides exchange transfer of matrix ATP for outside creatine kinase-supplied ADP when both substrates are simultaneously bound to translocase and (3) creatine kinase, starting these reactions when activated by the substrates from medium. The specific feature of this system is a close proximity of creatine kinase and translocase molecules. This results in high probability of direct activation of translocase by creatine kinase-derived ADP without its leak into the medium. In turn, the activated translocase with the same high probability directly provides creatine kinase with matrix-derived ATP. The catalytic complexes of creatine kinase with ATP from matrix together with those formed from substrates from medium provide high activation of creatine kinase coupled to translocase activation. The considered probabilities were arranged into a mathematical model. The model satisfactorily simulates the experimental data by Jacobus, W.E. and Saks, V.A. ((1982) Arch. Biochem. Biophys. 219, 167-178), who investigated this system in all regimens of functioning. The results suggest the observed kinetic and thermodynamic irregularities in the behavior of structurally-bound creatine kinase as a direct consequence of its tight coupling to translocase.

Adenosine Triphosphate↗

PubMed1988

Endogenous event-related potentials in monkey: the role of task relevance, stimulus probability, and behavioral response.

Monkeys were trained in auditory discrimination tasks resembling human paradigms in which long-latency endogenous components, such as P300, are typically recorded. Morphological, topographical, and functional properties of the monkey event-related potentials (ERPs) were analyzed to determine similarities and differences with human ERPs reported in the literature. ERPs were recorded from epidural electrodes in monkeys trained to produce operant responses. In a conditional discrimination (CD) task, tone pips (2 kHz or 6 kHz, 40 msec duration, and 60 dB above nHL) were presented every 4-8 sec. Target tones presented during 'time-in' (TI) were rewarded when followed by a response in the correct post-stimulus interval (400-3000 msec). In contrast, tones presented during 'time-out' (TO) were not rewarded. Under both conditions, tones elicited an initial frontally dominant triphasic complex (P56-N92-P157). Additionally, TI target tones followed by a response elicited a large negativity (N358) having maximal amplitude over mid-frontal regions and followed by a parietally distributed positivity (P658). The scalp distribution and covariation with task requirements of N358 resemble those reported for the human 'O' wave. ERPs were also recorded in an auditory oddball paradigm in which tone pips (2 kHz and 6 kHz, 40 msec duration, and 60 dB above nHL) were presented in random order every second. Monkeys trained in the CD paradigm, along with additional subjects, were trained to make delayed responses following target tones embedded in a background of different-pitch tones. Tone probabilities were varied in different sessions from 90-10, 70-30, to 50-50 to assess the effects of probability. Background and target tones elicited a triphasic complex (P52-N110-P159) similar in latency and distribution to that recorded in the CD task. Additionally, target tones in this paradigm elicited a long-latency positive component (LPC) that exhibited an inverse relationship with stimulus probability. LPC had an onset latency of approximately 150-200 msec, a duration of approximately 300 msec, and multiple peaks (P244 and P376). These data indicate the importance of stimulus context in eliciting long-latency endogenous activity. It further suggests that strong analogies exist between monkey and human potentials recorded under similar paradigms. The effects of task relevance, stimulus probability, and the act of producing behavioral responses are similar to the effects of these variables on analogous human potentials.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1994

Formula expressing a relationship among lesion thickness and time after diagnosis and survival probability in patients with malignant melanoma.

A microcomputer program in BASIC for predicting the survival probability as a function of lesion thickness and time after diagnosis is designed. The New York University-Melanoma Cooperative Group (NYU-MCG) shows 10-year survival rates of patients with malignant melanoma broken into four lesion-thickness groups (Cancer Journal for Clinicians, 41 (1991) 201-226). The formula used in this program is derived from the survival data of NYU-MCG. A mathematical 'probacent'-probability model previously published by the author is employed in this study. Analysis of the computer-assisted predicted and the NYU-MCG reported survival probability data indicates that the program is accurate and reliable with a close agreement in expressing survival probability and that it may be of value for prognostic evaluation of patients.

Humans↗

PubMed1989

Picture versus question elaboration on young children's learning of sentences containing high- and low-probability content.

The main purpose of the two experiments reported here was to compare the potency of two types of elaboration on children's learning of sentence content: The effects of partial picture adjuncts were compared to the effects produced by answering "why"-questions about the relationships specified in the sentences. Five- to seven-year-old children heard sentences of the form, subject/verb/direct object/preposition/instrument. Sentences contained either a high-probability or a low-probability instrument given the semantic context. In Experiment 1, sentences either were accompanied by a partial picture depicting the sentence action but omitting the instrument or were presented without a partial picture accompaniment. Recall was improved by provision of partial pictures at study. In Experiment 2, the sentences were accompanied by complete pictures depicting the sentence content. In both experiments, questioning significantly reduced recall of high-probability sentences, with recall of instruments affected especially negatively. Evidence is presented that insufficient attention to instruments may have been one mechanism mediating depressed recall of high- compared to low-probability instruments in the questioned conditions. In summary, partial pictures improved cued recall of sentences in this study; in contrast, all significant effects produced by answering why-questions were negative ones (i.e., later recall was reduced following interrogation at study).

Attention↗

PubMed1994

Pelagic food-web structure influences probability of mercury contamination in lake trout (Salvelinus namaycush).

An empirical model predicting probability of encountering levels of mercury in excess of 0.5 p.p.m. in lake trout (Salvelinus namaycush) is developed using logistic regression and two published data sets on food-web structures and elevated levels of mercury in sport fish. Probability of mercury contamination is a function of lake trout length and presence of pelagic forage fish. Presence of forage fish in a lake increased the odds that a lake trout of a given size would contain elevated levels of mercury in excess of eight times the expected level in lakes without pelagic forage fish. The model predicted a less than 5% probability of encountering elevated mercury levels in lake trout less than 30 cm in length from lakes with pelagic forage fish. In lakes where pelagic forage fish were absent, there was a less than 5% probability that lake trout under 45 cm would contain levels of mercury above 0.5 p.p.m.

Animals↗

PubMed1995

Probability of failure of orthodontic brackets bonded with different cementing agents.

OBJECTIVES: The aim of this study was to compare the maximum loads at failure and the probability of failure of three glass ionomer cements and a composite cement bonding orthodontic brackets to human premolar teeth. METHODS: The cements studied included a conventional glass ionomer cement, two resin-modified glass ionomer cements and a composite cement. The roots of 200 human premolar teeth were embedded in acrylic resin and the buccal enamel surface of the crown prepared as required. Each cement used to bond the bracket to the enamel was weighted, and light-cured where required. The specimens were stored for 10 min or 24 h at 37 degrees C and 100% humidity. A tensile shear force was applied via a wire loop placed under the wings of the bracket. The maximum load at failure was noted and subjected to Weibull analysis to compare probabilities of survival for each cement. The data obtained was also analyzed using a Kruskal-Wallis test followed by comparison of the groups using Mann-Whitney tests. RESULTS: Comparison of the loads at failure revealed that the composite cement was significantly stronger than the glass ionomer cements at 10 min and 24 h (p<0.05). Weibull analysis of the results gave values for the Weibull moduli and probabilities of survival for an orthodontic bracket under a given load for each cement at 10 min and 24 h. SIGNIFICANCE: . Glass ionomer cements give a number of clinically significant advantages over composite cement in the retention of brackets. The resin-modified glass ionomer cements tested had a higher probability of survival than the conventional cement tested at 24 h. However, further improvements in their early bond strength would be clinically beneficial.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1991

P300 from auditory and somatosensory stimuli: probability and inter-stimulus interval.

The P300 (P3) event-related brain potential (ERP) was elicited with auditory and somatosensory stimuli using an easy discrimination task in two experiments. Experiment 1 manipulated target stimulus probability (0.20 vs. 0.80). Experiment 2 manipulated inter-stimulus interval (2 s vs. 6 s) for both stimulus modalities in different conditions while keeping target probability constant. Probability and inter-stimulus interval had similar effects for auditory and somatosensory stimuli, with lower probability and longer inter-stimulus intervals producing larger P3 amplitudes. No statistically reliable differences in scalp distribution between modalities were obtained, with both modalities producing maximal amplitudes at Pz. The results suggest that auditory and somatosensory stimuli when used in a relatively easy discrimination task yield the same overall P3 values.

Acoustic Stimulation↗

PubMed1989

Computer-assisted predictive mathematical relationship between time after diagnosis and survival probability in patients with chronic leukemias.

A microcomputer program in BASIC for predicting the survival probability by the time after diagnosis in patients with chronic leukemias is designed. Formulas used in this program are derived from the data published by Feinleib and MacMahon (Blood 15 (1960) 332-349). A general equation previously published by the author is applied in this study to calculate the survival probability. Analysis of the computer-assisted predicted and Feinleib and MacMahon's observed data has shown that the program is fairly accurate and reliable with a close agreement in expressing survival probability as a function of the time after diagnosis. The computer-assisted predictive formulas can determine the relationship between the time and the survival probability, and may be of value for prognostic evaluation of patients with chronic leukemias.

Chronic Disease↗

PubMed1991

Meta-analysis for combining Bayesian probabilities.

Bayesian analysis is a method by which the reliability of diagnostic tests can be determined. It produces a probability of a patient having the disease given a positive test result (posterior probability). If more than one study of a given test's diagnostic accuracy is done, then how can we determine which of these studies has produced the most reliable posterior probability? Meta-analysis is a method whereby data from different studies can be combined. This paper proposes that meta-analysis more accurately estimates the true Bayesian posterior probability than other methods of data pooling.

Bayes Theorem↗

PubMed1990

Cisplatin and radiation: interaction probabilities and therapeutic possibilities.

This paper examines the probability of interactions occurring between drug lesions and radiation lesions in DNA for the cytotoxic and radiosensitizing agent cisplatin. The number of cisplatin-induced DNA adducts and radiation-induced strand breaks after a given dose of each agent are known for given cell systems, from which the probability that these lesions will interact can be estimated. Results of these calculations indicate that the probability of interaction could be high, depending on the distance over which two lesions can interact and the probability of repair of the interaction lesion. Calculated lesion numbers have been compared with known data on radiation modification, including illustrations of inconsistencies. In the second part of the paper, ways in which combined therapy with cisplatin and radiation can be improved are described. Development of methods to predict which types of tumor and which individual tumors within a given type are sensitive to the cytotoxic and radiosensitizing effects of the drug would aid rational selection of patients for combination treatments. Immunocytochemical methods sensitive enough to monitor cisplatin-DNA interactions in patients are available and may be useful in this context. The delivery and maintenance of higher tumour concentrations of radiosensitizer offers a further possibility for improvement. Studies of intratumoral injection of cisplatin have shown promise for achieving this goal while limiting normal tissue toxicity.

Cisplatin↗