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PubMed2004

Delay discounting and probability discounting as related to cigarette smoking status in adults.

This study examined relations between adult smokers and non-smokers and the devaluation of monetary rewards as a function of delay (delay discounting, DD) or probability (probability discounting, PD). The extent to which individuals discount value, either as a function of a reward being delayed or probabilistic, has been taken to reflect individual differences in impulsivity. Those who discount most are considered most impulsive. Previous research has shown that adult smokers discount the value of delayed rewards more than adult non-smokers. However, in the one published study that examined probability discounting in adult smokers and non-smokers, the smokers did not discount the value of probabilistic rewards more than the non-smoker controls. From this past research, it was hypothesized that measures of delay discounting would differentiate between smokers and non-smokers but that probability discounting would not. Participants were 54 (25 female) adult smokers (n = 25) and non-smokers (n = 29). The smokers all reported smoking at least 20 cigarettes per day, and the non-smokers reported having never smoked. The results indicated that the smokers discounted significantly more than the non-smokers by both delay and probability. Unlike past findings, these results suggest that both delay and probability discounting are related to adult cigarette smoking; however, it also was determined that DD was a significantly stronger predictor of smoking than PD.

Adult↗

PubMed1997

Orthodontic probability tables for black patients of African descent: mixed dentition analysis.

Mixed dentition space analyses form an essential part of orthodontic diagnostic procedures to determine the amount of space available for the accommodation of permanent teeth. The Moyers' probability tables for computing the sizes of unerupted canines and premolars were formulated at the University of Michigan from a sample consisting of northern European white subjects and are currently used worldwide. Because tooth sizes vary significantly between different population groups, it was the purpose of this study to construct relevant probability tables that would be more applicable to black subjects. Data were collected from a series of 100 randomly selected study models of black patients. The sample was equally subdivided by gender and all subjects had Angle Class I molar relationships with only minor malocclusions such as minor crowding, rotations, or diastemas. Two investigators independently measured the teeth on the study casts with a Vernier gauge that had sharpened calliper tips. Intraexaminer and interexaminer reliability was determined at 0.2 mm. All teeth to and including the first molars were measured. These data were then utilized in regression equations for both maxillary and mandibular arches, to enable the prediction of the mesiodistal widths of the canines and two premolars. The equations and predicted values were compared with those of the Moyers' probability tables, and significant differences (p <0.05) were found (except for the prediction of maxillary canines and premolars in females at the 85 and 95 percentile probability level). New probability tables for black subjects were formulated. It is envisaged that the proposed probability tables would be more accurate for black patients of African ancestry.

Adolescent↗

PubMed2002

Probabilities for a probabilistic network: a case study in oesophageal cancer.

With the help of two experts in gastrointestinal oncology from The Netherlands Cancer Institute, Antoni van Leeuwenhoekhuis, a decision-support system is being developed for patient-specific therapy selection for oesophageal cancer. The kernel of the system is a probabilistic network that describes the presentation characteristics of cancer of the oesophagus and the pathophysiological processes of invasion and metastasis. While the construction of the graphical structure of the network was relatively straightforward, probability elicitation with existing methods proved to be a major obstacle. To overcome this obstacle, we designed a new method for eliciting probabilities from experts that combines the ideas of transcribing probabilities as fragments of text and of using a scale with both numerical and verbal anchors for marking assessments. In this paper, we report experiences with our method in eliciting the probabilities required for the oesophagus network. The method allowed us to elicit many probabilities in reasonable time. To gain some insight in the quality of the probabilities obtained, we conducted a preliminary evaluation study of our network, using data from real patients. We found that for 85% of the patients, the network predicted the correct cancer stage.

Decision Support Techniques↗

PubMed2001

Adolescents' and adults' understanding of probability expressions.

PURPOSE: To examine whether there are differences between adolescents and adults in their interpretation of probability terms. METHODS: Participants were 20 fifth graders, 54 seventh graders, 45 ninth graders, and 34 young adults (mean adult age = 26.24 years, standard deviation = 2.09) from the San Francisco Bay area. They completed a self-administered survey asking them to assign percentage estimates (0% to 100%) to 30 randomly ordered probability terms. RESULTS: Significant age differences in the mean percentage estimates for 8 of the 30 terms were shown. Moreover, we found large variation in the interpretation of most probability terms studied, with larger variation among the adolescents than adults. Finally, all age groups had some difficulty correctly differentiating between "possibly" and "probably". CONCLUSIONS: Owing to wide variation in the interpretation of probability terms, both within and across age groups, we suggest health practitioners use percentages rather than probability terms to convey risk to both adolescents and adults.

Adolescent↗

PubMed1991

Fixation probability in spatially changing environments.

The fixation probability of a mutant in a subdivided population with spatially varying environments is investigated using a finite island model. This probability is different from that in a panmictic population if selection is intermediate to strong and migration is weak. An approximation is used to compute the fixation probability when migration among subpopulations is very weak. By numerically solving the two-dimensional partial differential equation for the fixation probability in the two subpopulation case, the approximation was shown to give fairly accurate values. With this approximation, we show in the case of two subpopulations that the fixation probability in subdivided populations is greater than that in panmictic populations mostly. The increase is most pronounced when the mutant is selected for in one subpopulation and is selected against in the other subpopulation. Also it is shown that when there are two types of environments, further subdivision of subpopulations does not cause much change of the fixation probability in the no dominance case unless the product of the selection coefficient and the local population size is less than one. With dominance, the effect of subdivision becomes more complex.

Biological Evolution↗

PubMed2006

Seeing the forest when entry is unlikely: probability and the mental representation of events.

Conceptualizing probability as psychological distance, the authors draw on construal level theory (Y. Trope & N. Liberman, 2003) to propose that decreasing an event's probability leads individuals to represent the event by its central, abstract, general features (high-level construal) rather than by its peripheral, concrete, specific features (low-level construal). Results indicated that when reported probabilities of events were low rather than high, participants were more broad (Study 1) and inclusive (Study 2) in their categorization of objects, increased their preference for general rather than specific activity descriptions (Study 3), segmented ongoing behavior into fewer units (Study 4), were more successful at abstracting visual information (Study 5), and were less successful at identifying details missing within a coherent visual whole (Study 6). Further, after exposure to low-probability as opposed to high-probability phrases, participants increasingly preferred to identify actions in ends-related rather than means-related terms (Study 7). Implications for probability assessment and choice under uncertainty are discussed.

Choice Behavior↗

PubMed2003

Conditionals and conditional probability.

The authors report 3 experiments in which participants were invited to judge the probability of statements of the form if p then q given frequency information about the cases pq, p not q, not pq, and not p not q (where not = not). Three hypotheses were compared: (a) that people equate the probability with that of the material conditional, 1 - P(p not q); (b) that people assign the conditional probability, P(q/p); and (c) that people assign the conjunctive probability P(pq). The experimental evidence allowed rejection of the 1st hypothesis but provided some support for the 2nd and 3rd hypotheses. Individual difference analyses showed that half of the participants used conditional probability and that most of the remaining participants used conjunctive probability as the basis of their judgments.

Color Perception↗

PubMed1985

Delineation of coding areas in DNA sequences through assignment of codon probabilities.

Codon usage tables have been produced for E. coli, yeast, human, and mouse. The nonrandom employment of codons allows assignment of probability values to trinucleotides in any DNA sequence. These values represent the probability that a given trinucleotide is used as a codon in the organism from which the table is derived. For the graphical delineation of coding areas in DNA sequences, a probability is assigned to each trinucleotide equal to its frequency in the codon table. Averaging and smoothing procedures then greatly enhance the detectability of areas of high average codon probability and better represent the mean codon probability. These manipulations increase graphical clarity without altering the overall magnitude of probabilities. Averaging introduces an error of less than 0.5% between "raw" and smoothed data. This graphical delineation of coding sequences does not depend on the presence of punctuation, ribosomal binding sites, etc: moreover the delineation of introns and exons is also possible.

Base Sequence↗

PubMed2005

Variations in jail sentences and the probability of re-arrest for driving while intoxicated.

OBJECTIVE: The probability of re-arrest for driving while intoxicated (DWI) is compared for four different groups of individuals classified by whether the individual was convicted and, if so, the type of sentence received. METHOD: Subsequent re-arrests for DWI were examined for all individuals whose index arrest for DWI had occurred between 1994 and 2001 in a county in New Mexico. The groups included (1) those convicted as a result of the index arrest and sentenced to a 28-day jail/treatment program (N (#)=(#) 2,703); (2) all those not convicted as a result of the index arrest (N = 709); (3) those who were convicted but not sentenced to jail (N = 1,047); and (4) those convicted and sentenced to jail (N = 1,290). RESULTS: Adjusting for covariates of BAC, number of prior arrests, ethnicity, age, and sex, the probability of not being re-arrested was greatest among those sentenced to the jail/treatment program (Group 1), next highest in the two groups convicted but not sentenced to jail/treatment (Groups 3 and 4), and lowest in the group that was not convicted (Group 2). Length of jail sentence among people convicted but not sentenced to the jail/treatment program was unrelated to the probability of re-arrest. CONCLUSION: Conviction for DWI, regardless of the sentence, appears to reduce the probability of re-arrest, and being sentenced to a multi-modal treatment/incarceration program further reduces the probability of re-arrest. However, the other types of sentences do not appear to differ in their impact on probability of re-arrest.

Adult↗

PubMed1999

Monte Carlo based protocol for cell survival and tumour control probability in BNCT.

A mathematical model to calculate the theoretical cell survival probability (nominally, the cell survival fraction) is developed to evaluate preclinical treatment conditions for boron neutron capture therapy (BNCT). A treatment condition is characterized by the neutron beam spectra, single or bilateral exposure, and the choice of boron carrier drug (boronophenylalanine (BPA) or boron sulfhydryl hydride (BSH)). The cell survival probability defined from Poisson statistics is expressed with the cell-killing yield, the 10B(n,alpha)7Li reaction density, and the tolerable neutron fluence. The radiation transport calculation from the neutron source to tumours is carried out using Monte Carlo methods: (i) reactor-based BNCT facility modelling to yield the neutron beam library at an irradiation port; (ii) dosimetry to limit the neutron fluence below a tolerance dose (10.5 Gy-Eq); (iii) calculation of the 10B(n,alpha)7Li reaction density in tumours. A shallow surface tumour could be effectively treated by single exposure producing an average cell survival probability of 10(-3)-10(-5) for probable ranges of the cell-killing yield for the two drugs, while a deep tumour will require bilateral exposure to achieve comparable cell kills at depth. With very pure epithermal beams eliminating thermal, low epithermal and fast neutrons, the cell survival can be decreased by factors of 2-10 compared with the unmodified neutron spectrum. A dominant effect of cell-killing yield on tumour cell survival demonstrates the importance of choice of boron carrier drug. However, these calculations do not indicate an unambiguous preference for one drug, due to the large overlap of tumour cell survival in the probable ranges of the cell-killing yield for the two drugs. The cell survival value averaged over a bulky tumour volume is used to predict the overall BNCT therapeutic efficacy, using a simple model of tumour control probability (TCP).

Boron Neutron Capture Therapy↗

PubMed2002

Interpretation of and preference for probability expressions among Japanese patients and physicians.

BACKGROUND: Patients and physicians often communicate using qualitative probability expressions that describe expected outcomes or risks of a medical intervention without knowing whether or not they share the same understanding. OBJECTIVE: The aim of the present study was to determine interpretations of qualitative probability expressions in clinical settings by Japanese patients and physicians as well as their assessments and preferences about physicians' use of such expressions. METHODS: One hundred and sixty-eight consecutive patients aged 16 years or older, who attended a university hospital during a 2-week period in 1999, and 156 physicians recruited through the Japanese General Medicine Research Network participated in this cross-sectional survey, using a self-administered questionnaire. Participants were asked to assign numerical interpretations as a percentage to 10 qualitative expressions of probability in two clinical situations related to prescribing a medicine for a cold and an anti-cancer drug. They were also asked which type of expression, qualitative or quantitative, they usually use when communicating probabilistic clinical information and which they prefer. RESULTS: The estimates of probability expressions showed wide variations, especially among patients. Patients tended to assign lower and higher values to highly positive and negative probability expressions, respectively, than physicians. Clinical context also influenced the estimation: both groups tended to assign higher estimates in the anti-cancer drug situation than in the cold treatment situation. Factor analysis revealed three psychologically meaningful factors in each situation. More patients than physicians (64.6% versus 50.3%) thought that physicians do not use numbers in routine practice. More than 20% of both patients and physicians considered that the actual use of qualitative terms by physicians is undesirable. Nevertheless, a sizable number of patients (41.4%) and physicians (15.2%) considered it preferable that physicians do not use numbers. CONCLUSION: Since interpretation of qualitative expressions of probability in Japanese is subject to large interpersonal variability and differences between patients and physicians, as well as context dependence, the use of qualitative expressions alone might cause misunderstanding among the parties involved. However, the majority of patients prefer words to numbers at present. Therefore, physicians, at least in Japan, ought to provide patients with both numbers and words when critical decisions need to be communicated.

Adolescent↗

PubMed2000

Cumulative probability of achieving an ongoing pregnancy after in-vitro fertilization and intracytoplasmic sperm injection according to a woman's age, subfertility diagnosis and primary or secondary subfertility.

The aim of this study was to estimate reliable cumulative probabilities of achieving an ongoing pregnancy after successive in-vitro fertilization or intracytoplasmic sperm injection (IVF/ICSI) cycles, according to a woman's age, subfertility diagnosis and primary or secondary subfertility. Therefore reasons for quitting treatment without achieving an ongoing pregnancy were taken into account. Moreover, we studied whether there were trends in cumulative probabilities after adjustment for potential confounding effects of the other two characteristics, duration of subfertility, year of first treatment and reason for quitting treatment. In total, 2984 IVF/ICSI cycles were performed in 1315 couples at the University Hospital Nijmegen, The Netherlands, between 1991 and 1998. The 'realistic' cumulative probability of achieving an ongoing pregnancy was 54.5% after five consecutive IVF/ICSI cycles, which was about 10% lower (absolute value) than the optimistic probability calculated by life-table analysis and about 10% higher (absolute value) than the most pessimistic estimate. Women of 35 years or younger had a higher probability of achieving an ongoing pregnancy than the older women. As ICSI is now an option, there were no obvious differences between the subfertility diagnosis subgroups. The cumulative probability after the first two IVF/ICSI cycles was higher in women with secondary subfertility than in those with primary subfertility; this advantage disappeared after further treatment. These trends remained valid after adjustment for confounding factors.

Adult↗

PubMed1994

Mortality probability models for patients in the intensive care unit for 48 or 72 hours: a prospective, multicenter study.

OBJECTIVE: To develop models in the Mortality Probability Model (MPM II) system to estimate the probability of hospital mortality at 48 and 72 hrs in the intensive care unit (ICU), and to test whether the 24-hr Mortality Probability Model (MPM24), developed for use at 24 hrs in the ICU, can be used on a daily basis beyond 24 hrs. DESIGN: A prospective, multicenter study to develop and validate models, using a cohort of consecutive admissions. SETTING: Six adult medical and surgical ICUs in Massachusetts and New York adjusted to reflect 137 ICUs in 12 countries. PATIENTS: Consecutive admissions (n = 6,290) to the Massachusetts/New York ICUs were studied. Of these patients, 3,023 and 2,233 patients remained in the ICU and had complete data at 48 and 72 hrs, respectively. Patients < 18 yrs of age, burn patients, coronary care patients, and cardiac surgical patients were excluded. OUTCOME MEASURE: Vital status at the time of hospital discharge. RESULTS: The models consist of five variables measured at the time of ICU admission and eight variables ascertained at 24-hr intervals. The 24-hr model demonstrated poor calibration and discrimination at 48 and 72 hrs. The newly developed 48- and 72-hr models--MPM48 and MPM72--contain the same 13 variables and coefficients as the MPM24. The models differ only in their constant terms, which increase in a manner that reflects the increasing probability of mortality with increasing length of stay in the ICU. These constant terms were adjusted by a factor determined from the relationship between the data from the six Massachusetts and New York ICUs and a more extensive data set, from which the ICU admission Mortality Probability Model (MPM0) and MPM24 were developed. This latter data set was assembled from ICUs in 12 countries. The MPM48 and MPM72 calibrated and discriminated well, based on goodness-of-fit tests and area under the receiver operating characteristic curve. CONCLUSIONS: Models developed for use among ICU patients at one time period are not transferable without modification to other time periods. The MPM48 and MPM72 calibrated well to their respective time periods, and they are intended for use at specific points in time. The increasing constant terms and associated increase in the probability of hospital mortality exemplify a common clinical adage that if a patient's clinical profile stays the same, he or she is actually getting worse.

Adult↗

PubMed1996

Erythrocyte sodium transport and the probability of having hypertension.

BACKGROUND: A number of alterations of ion transport and concentrations have been reported in erythrocytes from patients with hypertension and their young normotensive offspring. Of these, only sodium-lithium countertransport appears to be capable of predicting the effects of genetic variation on interindividual differences in blood pressure. OBJECTIVE: As a first step toward identifying other erythrocyte traits capable of predicting the effects of genetic variation on interindividual differences in blood pressure, we evaluated whether furosemide-sensitive sodium or potassium cotransport, ouabain-sensitive sodium pump, passive permeability to sodium or potassium, or intracellular concentrations of sodium or potassium are predictors of the probability of having hypertension in a general Caucasian population; we also attempted to confirm our previous inference that sodium-lithium countertransport is a predictor of the probability of having hypertension in this population. METHODS: The sample for analyses consisted of 199 unrelated men, aged 56-91 years, and 216 unrelated, nonpregnant women, aged 53-87 years, from the population of Rochester, Minnesota. Logistic regression was used to assess the relationship between predictor traits and blood pressure diagnostic status (normotension or hypertension). We assessed whether each erythrocyte trait was a predictor of the probability of having hypertension when the trait was considered by itself and when it was considered after the effects of other identified predictors of the probability of hypertension were included in the logistic regression models. RESULTS: When each erythrocyte trait was considered by itself, the predictors of the probability of having hypertension were sodium-lithium countertransport in men and sodium-lithium countertransport, sodium and potassium cotransport, and intracellular sodium concentration in women. When each erythrocyte trait was considered after other predictors had been included in the logistic regression models, none of the erythrocyte traits made an additional contribution to prediction of the probability of having hypertension unless its interactions with other predictors were also included in the models. CONCLUSIONS: Multiple measures of erythrocyte ion transport are associated with hypertension in the general Caucasian population; however, most of these associations are context-dependent inasmuch as they are gender-specific and dependent on levels of other predictor traits.

Aged↗

PubMed1994

The 1-month outcome of patients with a low probability Technegas ventilation/perfusion lung scan.

The objective was to study the 1-month outcome of patients who had a low probability ventilation/perfusion lung scan using Technegas radioaerosol as the inhalational agent and who did not receive anticoagulation. One hundred consecutive patients with suspected pulmonary embolism were studied retrospectively. Their Technegas lung scans were classified by two blinded and independent nuclear medicine physicians and the medical records of all patients with a low probability scan were reviewed. One hundred inpatients (42 males and 58 females) with a mean age of 63 years were studied. The three most common clinical presentations leading to lung scintigraphy were unexplained dyspnoea (30 cases), unexplained dyspnoea with pleuritic chest pain (26 cases) and pleuritic chest pain only (15 cases). Nine patients had been judged by their managing medical team to have a high clinical probability of true pulmonary embolism, 32 had an intermediate probability clinical presentation and 59 a low clinical probability of pulmonary embolism. None of the 100 patients experienced further episodes of suspected or proven pulmonary embolism during the follow-up period. Six patients died. In none of them was pulmonary embolism either the cause of or a major contributing factor to death. The finding of a low probability scan using Technegas as the ventilation scintigram agent of choice describes a group of patients who, even in the absence of therapeutic anticoagulation, have a favourable 1-month outcome free of either true or suspected clinical pulmonary embolism. Invasive, pulmonary angiography-based diagnostic strategies may not be needed in this group of patients.

Female↗

PubMed1999

The probability of HLA-C matching between patient and unrelated donor at the molecular level: estimations based on the linkage disequilibrium between DNA typed HLA-B and HLA-C alleles.

BACKGROUND: Recent evidence suggests a more significant role of HLA-C as a target of alloreactions after bone marrow transplantation than previously suspected. Although linkage disequilibrium (LD) between HLA-B and -C serogroups is well documented, the level of LD at the allelic level is not known. In this study, we determine the LD between HLA-B and -C alleles and estimate the probability of molecular HLA-C matching between unrelated individuals who match for both HLA-B alleles. METHODS: The study included 727 haplotypes from 849 individuals who were HLA-A, -B, -C and -DRB1 typed by high-resolution PCR-SSOP technique. Zelterman's statistic was used to test for global LD between HLA loci. LD between specific HLA-B and -C allelic combinations was calculated from their observed and expected frequencies in the study haplotypes. The probability of HLA-C matching for specific HLA-B allele was estimated from contingency table generated from the HLA-B and -C haplotypes. RESULTS: HLA-C was found to exist in LD with HLA-A and -B, as well as -DRB1, loci; however, it was strongest between HLA-B and -C loci. A marked variability in the level of LD between specific HLA-B and -C alleles was noticed. A strong LD was seen in some allele pairs like B*0702-C*w0702, B*3501-Cw*0401, and B*0801-Cw*0701. The overall estimated probability of HLA-C matching between unrelated individuals that match for both HLA-B alleles is 42.25%. For 237 (72.9%) of 325 combinations involving the 25 commonest HLA-B alleles, the estimated probability that the HLA-B-matched unrelated individuals will match for both HLA-C alleles is less than 50%. In addition, a 100% probability of matching for both HLA-C alleles is expected only if both individuals bear either B*0801/ B*0801 or B*4901/B*4901 or B*0801/B*4901. Probability tables for common alleles are presented. CONCLUSIONS: We conclude that, despite matching for both HLA-B alleles by high resolution DNA typing and the presence of a strong LD between HLA-B and HLA-C loci, unrelated individuals are more likely to mismatch rather than match for one or both HLA-C alleles.

Alleles↗

PubMed2006

The probability of glaucoma from ocular hypertension determined by ophthalmologists in comparison to a risk calculator.

OBJECTIVE: To investigate the ability of ophthalmologists to estimate an individual's risk of converting from ocular hypertension to glaucoma, and to compare these estimates to a risk calculator. DESIGN: Cross-Sectional Survey. METHODS: Fifty-one ophthalmologists estimated the probability of developing glaucoma of 4 factitious patients with ocular hypertension, after a didactic review of the Ocular Hypertension Treatment Study (OHTS) results. We compared the physician estimates to the probability estimates of a risk calculator on the basis of the multivariate Cox proportional hazard model of the OHTS results. RESULTS: The average estimates given by the ophthalmologists (mean probability+/-SD) of developing glaucoma in 5 years for patient no. 1, patient no. 2, patient no. 3, and patient no. 4 were 6.5%+/-8.4 (range 1 to 50), 30.6%+/-20.5 (range 1 to 100), 7.1%+/-5.1 (range 0 to 20), and 21.1%+/-17.3 (range 1 to 80), respectively. The risk calculator estimated the probability of glaucoma in these same patients to be 13.7%, 53.8%, 5.1%, and 41.9%, respectively. CONCLUSIONS: The ophthalmologists showed a high range of estimates for the probability of developing glaucoma in the same ocular hypertensive patients. This may lead to either under or over treatment of patients. Clinicians need a more exact method to determine the probability of glaucoma from ocular hypertension.

Aged↗

PubMed2004

Dynamic probability estimator for machine learning.

An efficient algorithm for dynamic estimation of probabilities without division on unlimited number of input data is presented. The method estimates probabilities of the sampled data from the raw sample count, while keeping the total count value constant. Accuracy of the estimate depends on the counter size, rather than on the total number of data points. Estimator follows variations of the incoming data probability within a fixed window size, without explicit implementation of the windowing technique. Total design area is very small and all probabilities are estimated concurrently. Dynamic probability estimator was implemented using a programmable gate array from Xilinx. The performance of this implementation is evaluated in terms of the area efficiency and execution time. This method is suitable for the highly integrated design of artificial neural networks where a large number of dynamic probability estimators can work concurrently.

Artificial Intelligence↗