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PubMed1994

Quantification of fetal heart rate variation using a probability distribution matrix.

Analysis of FHR variability attempts to be able to distinguish which FHR changes are physiological and which are pathological. From the results of such studies, it is hoped that clinicians will be provided with the means to identify accurately which fetuses are healthy, which are at risk and which are actually in distress at any gestational age. The probability distribution matrix presented has the outstanding advantage of enabling one to condense any amount of FHR data into one uniform description for analysis en bloc. Not even one FHR is sacrificed; each one contributes to the FHR vs. DFHR distribution pattern. Where the probability distribution matrix is made from many FHR samples taken from healthy fetuses under natural day-to-day maternal circumferences, as we have done, this matrix can be considered as a physiologically unbiased reference. The subtraction matrix is characterized by the difference in FHR vs. DFHR distribution patterns between two probability distribution matrices compared, representing the equal residue of net absolute value. The larger the difference in FHR vs. DFHR distribution between two probability distribution matrices, the larger these kinds of residue values, and if two probability distribution matrices are identical, all the elements in the subtraction matrix indicate the residue values of zero. Our probability distribution matrix approach confirms the results of previously reported studies which utilized other analytical strategies. Therefore, we can evaluate quantitatively age-related FHR changes used as variables, such as the subtraction matrix and difference rate. By varying intervals between paired FHRs (e.g. selecting the original FHR--skip--select the following FHR--skip 2 FHR--select the next FHR, etc.), the probability distribution matrix could be adopted as a general tool for analysis of sequential changes in large numbers of FHR for further studies.

Bias↗

PubMed2001

Prevalence corrected hysterectomy rates and probabilities in Utah.

PURPOSE: A life table method is used for correcting hysterectomy rates and probabilities for prevalent cases of hysterectomies in the population. Both corrected and conventional hysterectomy rates and probabilities are reported. METHODS: Hysterectomy prevalence estimates are derived from cross-sectional hysterectomy and mortality using a life table method. Analysis is based on the Utah Hospital Discharge Data Base and State death certificates. RESULTS: Hysterectomy rates are strongly influenced by age, reaching 150 per 10,000 for ages 45-49 years. The corresponding corrected hysterectomy rate is 196. Differences between the corrected and uncorrected cause-specific hysterectomy rates tend to be most pronounced at their peaks, particularly later in life where the prevalence of hysterectomy is greatest. Probability of hysterectomy approaches slightly above 35% over the life span, whereas the corrected hysterectomy probability approaches 43%. Probability of hysterectomy in the next 10 years is 12.9% for women aged 35 years and 11.7% for women aged 45 years. Corresponding corrected hysterectomy probabilities are 14.3 and 15.1. Higher prevalence of hysterectomy in later ages explains the reverse in magnitude of the rates when the correction is applied to the hysterectomy rates. CONCLUSIONS: Conventional hysterectomy rates are underestimated, particularly in older age groups. A prevalence correction of the rates and probabilities is necessary to fully understand the potential health related consequences and impact of this medical procedure in the population.

Adult↗

PubMedDate not supplied

Comparison of probability and likelihood models for peptide identification from tandem mass spectrometry data.

We evaluate statistical models used in two-hypothesis tests for identifying peptides from tandem mass spectrometry data. The null hypothesis H(0), that a peptide matches a spectrum by chance, requires information on the probability of by-chance matches between peptide fragments and peaks in the spectrum. Likewise, the alternate hypothesis H(A), that the spectrum is due to a particular peptide, requires probabilities that the peptide fragments would indeed be observed if it was the causative agent. We compare models for these probabilities by determining the identification rates produced by the models using an independent data set. The initial models use different probabilities depending on fragment ion type, but uniform probabilities for each ion type across all of the labile bonds along the backbone. More sophisticated models for probabilities under both H(A) and H(0) are introduced that do not assume uniform probabilities for each ion type. In addition, the performance of these models using a standard likelihood model is compared to an information theory approach derived from the likelihood model. Also, a simple but effective model for incorporating peak intensities is described. Finally, a support-vector machine is used to discriminate between correct and incorrect identifications based on multiple characteristics of the scoring functions. The results are shown to reduce the misidentification rate significantly when compared to a benchmark cross-correlation based approach.

Databases, Protein↗

PubMed2000

Violence risk assessment and risk communication: the effects of using actual cases, providing instruction, and employing probability versus frequency formats.

This article describes studies designed to inform policy makers and practitioners about factors influencing the validity of violence risk assessment and risk communication. Forensic psychologists and psychiatrists were shown case summaries of patients hospitalized with mental disorder and were asked to judge the likelihood that the patient would harm someone within six months after discharge from the hospital. They also judged whether the patient posed a high risk, medium risk, or low risk of harming someone after discharge. Studies 1 and 2 replicated, with real case summaries as stimuli, the response-scale effects found by Slovic and Monahan (1995). Providing clinicians with response scales allowing more discriminability among smaller probabilities led patients to be judged as posing lower probabilities of committing harmful acts. This format effect was not eliminated by having clinicians judge relative frequencies rather than probabilities or by providing them with instruction in how to make these types of judgments. In addition, frequency scales led to lower mean likelihood judgments than did probability scales, but, at any given level of likelihood, a patient was judged as posing higher risk if that likelihood was derived from a frequency scale (e.g., 10 out of 100) than if it was derived from a probability scale (e.g., 10%). Similarly, communicating a patient's dangerousness as a relative frequency (e.g., 2 out of 10) led to much higher perceived risk than did communicating a comparable probability (e.g., 20%). The different reactions to probability and frequency formats appear to be attributable to the more frightening images evoked by frequencies. Implications for risk assessment and risk communication are discussed.

Adult↗

PubMedDate not supplied

The probability of conception on different days of the cycle with respect to ovulation: an overview.

Several mathematical models have been developed over the past thirty years to investigate how the probability of conception changes on the different days of the cycle with respect to ovulation. A problem general to all models is to estimate the day of ovulation. Since the most fertile days are those close to ovulation, less precise estimates of this event will lead to less accurate estimates of the probability of conception on a given day of the cycle. Given that a reference point for ovulation is available, the first model considered conception as dependent only on the timing of intercourse. Conception was found to be most likely to occur on only six days in each cycle. However, the model is biologically unrealistic because it assumes that all ova can be fertilized and lead to a viable pregnancy. There are other factors that affect the probability of conception, including whether the ovum is viable or not. Recent models have extended the idea of cycle viability to allow for differences between cycles within couples and for the introduction of couple specific covariates. In a second group of models the probability of conception depends mainly on the time of intercourse and the survival times of sperm and ovum. A graphical summary of the results available in the literature is presented. Conception probabilities have been found to be significantly different from zero from five days before ovulation to the day of ovulation itself. On average, less than half of the cycles are viable in women, although recent studies suggest that different cycle viability between women should be taken into account. Survival times for sperm and the ovum have been estimated to be 1.4 days and 0.7 days, respectively. Sperm would have a 5% probability of surviving more than 4.4 days and a 1% probability of surviving more than 6.8 days.

Female↗

PubMed1991

Representativeness and conjoint probability.

People commonly violate a basic rule of probability, judging a conjunction of events to be more probable than at least 1 of its component events. Many manifestations of this conjunction fallacy have been ascribed to people's reliance on the representativeness heuristic for judging probability. Some conjunction fallacies, however, have been ascribed to the incorrect rules people use to combine probabilities. In 2 experiments, representativeness was pitted against probability combination to determine the contributions of each to the fallacy. Even for exemplar representativeness problems, the fallacy stemmed primarily from the application of incorrect combination rules. Representativeness seemed to be involved only insofar as it influenced the probabilities of a conjunction's component events. Implications of these findings are discussed for the representativeness account of judgmental errors and the relation between similarity and probability.

Humans↗

PubMed1988

Components of the location probability effect in visual search tasks.

In visual search tasks, targets are detected more rapidly when they appear in locations that commonly contain a target than when they appear in locations that rarely contain a target. Five experiments were conducted to investigate two specific properties of this location probability effect: its dependence on spatial location versus relative position and its dependence on or independence of target identity. In Experiment 1 spatial location of a stimulus row was varied to determine whether high location probability facilitates target detection in a particular location in visual space or a particular relative position within the row. Both were facilitated to approximately the same extent. In Experiment 2 an inducing target occurred with high probability in one of four display locations, and a test target occurred with equal probability in all four locations. Both targets were found more quickly in the high-probability location than in the other locations, but the advantage associated with targets in the high-probability location was larger for the inducing target than for the test target. In Experiments 3-5 the correspondence between the components observed in Experiments 1 and 2 was examined. The overall pattern of results was compatible with a model in which the location probability effect is produced partly by an attentional spotlight, which facilitates processing of any stimulus appearing in a particular location in visual space, and partly by a network of position-specific letter detectors, which facilitates detection of a particular letter in a particular relative position within a display. Models with flexible scanning strategies were also considered.

Attention↗

PubMed2000

Perceived probability, perceived severity, and health-protective behavior.

It seems obvious that 2 key attributes of health hazards, their perceived probability and perceived severity, do not act independently on the motivation to engage in protective behavior. If a health problem is perceived to have no chance of occurring, there should be no interest in acting against it, regardless of how serious it might be. Nevertheless, researchers seldom observe the expected interaction between probability and severity. A case study approach was used to examine how probability and severity combine to influence interest in protection. Ratings of motivation to act, probability, and severity for 201 hazards were collected from 12 participants, and data were analyzed for each person separately. Analyses revealed the expected Probability x Severity interaction. Additional calculations showed why it is difficult to detect this interaction using between-subjects designs. The data also revealed that people are surprisingly insensitive to variations in hazard probability when probabilities are in the moderate to high range.

Adult↗

PubMed2005

Branch-length prior influences Bayesian posterior probability of phylogeny.

The Bayesian method for estimating species phylogenies from molecular sequence data provides an attractive alternative to maximum likelihood with nonparametric bootstrap due to the easy interpretation of posterior probabilities for trees and to availability of efficient computational algorithms. However, for many data sets it produces extremely high posterior probabilities, sometimes for apparently incorrect clades. Here we use both computer simulation and empirical data analysis to examine the effect of the prior model for internal branch lengths. We found that posterior probabilities for trees and clades are sensitive to the prior for internal branch lengths, and priors assuming long internal branches cause high posterior probabilities for trees. In particular, uniform priors with high upper bounds bias Bayesian clade probabilities in favor of extreme values. We discuss possible remedies to the problem, including empirical and full Bayesian methods and subjective procedures suggested in Bayesian hypothesis testing. Our results also suggest that the bootstrap proportion and Bayesian posterior probability are different measures of accuracy, and that the bootstrap proportion, if interpreted as the probability that the clade is true, can be either too liberal or too conservative.

Bayes Theorem↗

PubMedDate not supplied

Probabilities of heart donors arising within specified times for child recipients.

AIM: To determine the availability of donor hearts for children of different blood group and weight needing urgent heart transplantation. METHODS: Data maintained by the Australia and New Zealand Organ Donor Registry 1989-2004 were analysed to determine the frequency of donation. Probabilities of suitable donor availability within 10, 20, 30, 40, 60, 90 and 180 days were estimated using a Poisson model with the assumptions that traditional ABO blood compatibilities applied, suitable donors were 0.8-4.0 times the recipient's body weight (BW) and suitable adult donors were aged <40 years. RESULTS: Probabilities of suitable donor availability increase with passage of time from 10 to 180 days and decrease with competition from other needful recipients. Maximum suitable donor availability occurs for children of all blood groups at body weight 20 kg. The probabilities of a donor heart arising within 40 days (maximum safe duration of extracorporeal membrane oxygenation support locally available for young children) for this recipient body weight according to blood group is 0.89, 0.85, 0.73, 0.67 (AB, A, B, O). Probabilities for recipients of BW 3 kg and 60 kg respectively are 0.16, 0.14, 0.10, 0.09 (AB, A, B, O) and 0.66, 0.61, 0.47, 0.42 (AB, A, B, O). CONCLUSION: Expectation of suitable heart donation arising within 40 days for needful recipients in Australia is low for infants (probability <0.3), moderate for small children (probability 0.5-0.9) and modest for large children (probability 0.4-0.7), with variation at all body weights according to blood group and waiting time.

Blood Grouping and Crossmatching↗

PubMed2006

When does information about probability count in choices under risk?

The question addressed in the present research is whether in naturalistic risky decision environments people are sensitive to information about the probability parameter. In Study 1, we showed that in naturalistic scenarios participants generally revealed little interest in obtaining information about the outcomes and probabilities. Moreover, participants asked fewer questions about probabilities for scenarios containing moral considerations. In Study 2, it was shown that, when supplied with information on probabilities, people could be sensitive to this information. This sensitivity depends on two factors. People were less sensitive to probabilities in scenarios perceived as containing ethical considerations. People were also less sensitive to probabilities when they were faced with a single-choice situation than when they were faced with a series of lotteries with different probabilities. This can be accounted for in terms of the evaluability principle.

Adult↗

PubMed2002

Validation of the Canadian clinical probability model for acute venous thrombosis.

OBJECTIVE: To validate the predictive value of the Canadian clinical probability model for acute venous thrombosis, which, to the best of the authors' knowledge, has not been done in emergency department (ED) settings outside of Canada. METHODS: Demographic and clinical information, rapid D-dimer testing, and venous ultrasound imaging were obtained among patients presenting with clinically suspected venous thrombosis at a university-affiliated ED. A diagnosis of deep venous thrombosis (DVT) was made based on venous ultrasound test results or objectively documented venous thromboembolism during a 12-week follow-up period. The probability of venous thrombosis was calculated using the Canadian clinical probability model. RESULTS: Among 102 patients, 17 (17%) were diagnosed as having venous thrombosis initially or during the three-month follow-up period. The frequency of venous thrombosis among patients categorized as having high probability was 10 of 17 [59%, 95% confidence interval (95% CI) = 35% to 82%], 6 of 44 (14%, 95% CI = 4% to 24%) with intermediate probability, and 1 of 41 (2%, 95% CI = 0.1% to 11%) with low probability. This compares with respective values of 49%, 14%, and 3%, reported by Canadian researchers in an ED study. Forty-one of 102 (40%) patients had an alternate diagnosis as likely or more likely than venous thrombosis, but only three (7%, 95% CI = 2% to 18%) of these had venous thrombosis. CONCLUSIONS: Use of the Canadian probability model for DVT in this ED resulted in effective risk stratification, comparable to previously published results.

Adult↗

PubMed2004

Probability of transmitter release at neocortical synapses at different temperatures.

The probability of transmitter release at synaptic terminals is one of the key characteristics of communication between nerve cells because it determines both the strength and dynamic properties of synaptic connections. To assess the distribution of the release probabilities at excitatory synapses on supragranular pyramidal cells in rat visual cortex, we have used the MK-801, a blocker of the open N-methyl-d-aspartate (NMDA) receptor-gated channels. With this method, the release probability can be calculated from the time course of the blockade of NMDA-receptor mediated postsynaptic currents in the presence of MK-801. At temperatures >32 degrees C, the distribution of release probabilities covered the range from 0.05 to 0.43 [mean: 0.171 +/- 0.012 (SE), n = 65], being skewed toward low values. When estimated at room temperature (22-25 degrees C), the release probabilities were significantly lower (mean: 0.123 +/- 0.009, n = 54), and almost the whole distribution was restricted to values <0.2. Furthermore, warming from room temperature to >32 degrees C led to a pronounced overshooting increase of the release probability. Taken together, the results of the present study show that release probabilities at synapses formed onto layer 2/3 pyramidal cells in the visual cortex vary significantly, but values >0.3 are rare and the results obtained either at room or variable temperature differ significantly from those made under conditions of constant temperature in the physiological range.

Animals↗

PubMedDate not supplied

Verbal expressions of probability in informed consent litigation.

Informed consent litigation provides a forum in which probabilistic evidence is elicited from physicians as parties or as expert witnesses. The authors reviewed over 450 medical informed consent opinions reported by both trial and appellate courts in all 50 states over 40 years to determine 1) the extent to which verbal expressions of probability were used by testifying physicians to characterize the risks of medical procedures; 2) when such expressions were used, whether consistent numeric interpretations of the terms were being applied by the physicians; 3) whether the choice of expression was influenced by the severity of the consequences associated with the particular risk; and 4) whether the use of such terms was correlated with trial outcomes, inasmuch as the duty to disclose a risk is said to increase with the magnitude of the risk and probability is one measure of such magnitude. It was found that subjective verbal expressions of probability are used in the litigation setting, and that such expressions represent broad ranges of numeric probabilities. There was some correlation between the expression and the represented numeric probabilities. In general, expressions such as "extremely low" and "low" corresponded to probabilities lower than those represented by terms such as "high" and "very high." Further, verbal expressions appeared to be influenced by the severity of the consequences associated with the risks, but whether this increases or decreases the ambiguity of verbal expressions in the communication process warrants further research. The authors suggest a syntax of verbal expressions of probability as a means to reduce the numeric ambiguity of these terms.

Choice Behavior↗

PubMed2006

Using probability vs. nonprobability sampling to identify hard-to-access participants for health-related research: costs and contrasts.

This article compares the recruitment costs and participant characteristics associated with the use of probability and nonprobability sampling strategies in a longitudinal study of older hemodialysis patients and their spouses. Contrasts were made of people who accrued to the study based on probability and nonprobability sampling strategies. Probability-based sampling was more time-efficient and cost-effective than nonprobability sampling. There were no significant differences between the respondents identified through probability and nonprobability sampling on age, gender, years married, education, work status, and professional job status. Respondents from the probability sample were more likely to be Protestant and less likely to be Catholic than those from the nonprobability sample. Respondents from the probability sample were more likely to be Black, whereas those from the nonprobability sample were more likely to be White. There are strengths and shortcomings associated with both nonprobability and probability sampling. Researchers need to consider representativeness and external validity issues when designing sampling and related recruitment plans for health-related research.

Aged↗

PubMed2002

A method of probability diagnostic assignment that applies bayes theorem for use in serologic diagnostics, using an example of Neospora caninum infection in cattle.

OBJECTIVE: To develop a method of probability diagnostic assignment (PDA) that uses continuous serologic measures and infection prevalence to estimate the probability of an animal being infected, using Neospora caninum as an example. ANIMALS: 196 N caninum-infected beef and dairy cattle and 553 cattle not infected with N caninum; 50 dairy cows that aborted and 50 herdmates that did not abort. PROCEDURE: Probability density functions corresponding to distributions of N caninum kinetic ELISA results from infected and uninfected cattle were estimated by maximum likelihood methods. Maximum likelihood methods also were used to estimate N caninum infection prevalence in a herd that had an excessive number of abortions. Density functions and the prevalence estimate were incorporated into Bayes formula to calculate the conditional probability that a cow with a particular ELISA value was infected with N caninum. RESULTS: Probability functions identified for infected and uninfected cattle were Weibull and inverse gamma functions, respectively. Herd prevalence was estimated, and probabilities of N caninum infection were determined for cows with various ELISA values. CONCLUSIONS AND CLINICAL RELEVANCE: Use of PDA offers an advantage to clinicians and diagnosticians over traditional seronegative or seropositive classifications used as a proxy for infection status by providing an assessment of the actual probability of infection. The PDA permits use of all diagnostic information inherent in an assay, thereby eliminating a need for estimates of sensitivity and specificity. The PDA also would have general utility in interpreting results of any diagnostic assay measured on a continuous or discrete scale.

Abortion, Veterinary↗

PubMed2003

Signal probability effects on error detection performance in a quality control task.

This study was designed to examine the influence of signal probability on detection accuracy in a quality control task patterned after the checking of prescriptions in a pharmacy. Signal probability was defined as the ratio of erroneous scripts to correct scripts. 91 participants were either exposed to signal probabilities ranging from 26 to 30% ("low probability") or 34 to 38% ("high probability") while checking two sets of 40 simulated scripts for accuracy. Wrong item, wrong number, and wrong label information errors were possible, and performance was measured in terms of sensitivity (percentage of errors detected) and specificity (percentage of correct orders accepted). Analysis indicated that sensitivity was significantly worse for participants in the high signal probability condition, but specificity was not significantly different between signal probability conditions. Connections to existing theory and future directions for research are discussed.

Adult↗

PubMed1999

The conditional probability of survival of patients with primary malignant brain tumors: surveillance, epidemiology, and end results (SEER) data.

BACKGROUND: Five-year survival estimates in standard cancer reports provide a general description of disease outcome that is useful for surveillance and comparison purposes. However, for cancer survivors these overall survival rates may be discouraging, and the relevant question regarding an individual is this: Once he or she has survived for a specified period of time, what is the probability of survival over the next period of time? METHODS: To address this, conditional survival rates by histology for malignant brain tumor survivors were estimated using the SEER public use data and the Portable Survival System, with 19,105 brain and other nervous system patients diagnosed between 1979 and 1993. Given that the survival curve declines more rapidly in the first 2 years than in subsequent years, conditional probabilities of surviving 5 years given survival to 2 years and 95% confidence intervals (CIs)were calculated. As age is a strong prognostic factor for these tumors, conditional probabilities were also estimated by categories of age. RESULTS: Estimated 2- and 5-year relative survival rates for patients with malignant brain and other CNS tumors were 36.2% and 27.6%; however, the conditional probability of surviving to 5 years, given survival to 2 years, reaches 76.2% (95% CI: 74.8-77.6). Conditional probabilities varied by histology and age at diagnosis. The conditional probability of surviving 5 years after surviving 2 years was 67.8% (95% CI: 62.6-73.1) for patients with anaplastic astrocytomas, 36.4% (95% CI: 31.9-41.6) for patients with glioblastomas, and 79.8% (95% CI:75.3-84.1) for patients with medulloblastomas. CONCLUSIONS: Conditional probabilities provide important and encouraging information for those who are brain tumor survivors. The utility of these estimates for other time intervals and other cancers or diseases should be considered.

Adult↗