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PubMed2000

A comparison of the pattern- and total deviation-based Glaucoma Change Probability programs.

PURPOSE: To compare the rates of progression of visual field defects in glaucoma patients, by using the Glaucoma Change Probability program based on pattern deviation and total deviation probability maps. METHODS: The incidence of progression of visual field loss among 67 eyes of 56 glaucoma patients with an average of 6 years of follow-up was estimated by applying the criteria set by the Early Manifest Glaucoma Treatment study, which uses the output from the Glaucoma Change Probability (GCP) program of the Humphrey Field Analyzer (San Leandro, CA) based on pattern deviation probability maps. This incidence estimate was compared with one obtained by applying the same criteria but using the GCP program based on total deviation probability maps. RESULTS: The 6-year incidence of progression among patients with glaucoma was 23.2% and 35.7% using the GCP program based on pattern deviation and total deviation probability maps, respectively. Not all patients in whom visual field loss progressed according to pattern deviation also showed progression according to total deviation. CONCLUSIONS: The GCP program based on pattern deviation probability maps appears to screen out patients in whom progression of visual field defects may be due to diffuse loss from cataract, but the pattern deviation maps may also be identifying other types of field loss not detected by the total deviation maps.

Disease Progression↗

PubMed1992

Postoperative subconjunctival 5-fluorouracil injections and success probability of trabeculectomy in Japanese: results of 5-year follow-up.

The effects of postoperative subconjunctival 5-fluorouracil (5-FU) injections on the surgical outcome of trabeculectomy in the Japanese were studied in a total of 362 eyes of 263 glaucoma patients with the postoperative follow-up of 1-9 years. The probability of successful intraocular pressure (IOP) control at the 5-year point of the continuing follow-up was calculated by the life-table method of Kaplan-Meier. The eyes that had undergone trabeculectomy with postoperative injections of 5-FU (5-FU group) included 165 eyes with primary open-angle glaucoma (POAG), 38 eyes with secondary glaucoma (SG) and 60 eyes with refractory glaucoma. The eyes that had undergone trabeculectomy without postoperative 5-FU (control group) included 46 eyes with POAG, 31 eyes with SG and 22 eyes with refractory glaucoma. The surgical techniques and postoperative care were virtually identical between the two groups, except that the control group did not receive the postoperative 5-FU. The total amount of 5-FU given to each case averaged 36.5, 36.0 and 49.5 mg for POAG, SG and refractory glaucoma, respectively. At the 5-year follow-up point, the probability of maintaining IOP control below 21 mmHg with or without medication in the 5-FU group was 92.5% for POAG, 87.4% for SG and 57.5% for refractory glaucoma; while without medication the probability was 58.2, 54.8 and 27.8%, respectively. The probability of IOP control below 16 mmHg with or without medication in the 5-FU group was 77.9% for POAG, 66.8% for SG and 26.9% for refractory glaucoma; without medication the probability was 55.2, 49.8 and 24.5%, respectively. In the control group, the corresponding probability for each type of glaucoma was much lower than that in the 5-FU group, and the probability for IOP control below 16 mmHG was 0.12% at the 5-year follow-up point. In the 5-FU group, the mean postoperative IOP in successfully treated eyes remained at about 12 mmHg throughout the first 5 years of the follow-up period. There was no significant difference in incidence of postoperative complications between the 5-FU and control groups, except that corneal epithelial defect was noted in 38.8% of the eyes in the 5-FU group. No late complications related to the use of postoperative 5-FU were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMedDate not supplied

[Effects of prefrontal ablations on the reaction of the active choice of feeder under different probability and value of the reinforcement on dog].

The role of the prefrontal cortex was investigated on the reaction of the active choice of the two feeders under changes value and probability reinforcement. The experiments were performed on 2 dogs with prefrontal ablation (g. proreus). Before the lesions the dogs were taught to receive food in two different feeders to conditioned stimuli with equally probable alimentary reinforcement. After ablation in the inter-trial intervals the dogs were running from the one feeder to another. In the answer to conditioned stimuli for many times the dogs choose the same feeder. The disturbance of the behavior after some times completely restored. In the experiments with competition of probability events and values of reinforcement the dogs chose the feeder with low-probability but better quality of reinforcement. In the experiments with equal value but different probability the intact dogs chose the feeder with higher probability. In our experiments the dogs with prefrontal lesions chose the each feeder equiprobably. Thus in condition of free behavior one of different functions of the prefrontal cortex is the reactions choose with more probability of reinforcement.

Animals↗

PubMed1993

Calculating the probability of rare events: why settle for an approximation?

OBJECTIVE: Health services researchers often need to compute the probability of observing a certain number of events when only a few such events are expected. Our objective is to show that the standard approaches (Poisson, binomial, and normal approximations) are inappropriate in such instances, and to suggest an alternative. DATA SOURCES: Patients undergoing cholecystectomy (34,234) in 465 California hospitals in 1983 are used to demonstrate the biases arising from various methods of calculating the probability of observing a given number of deaths in each hospital. Similar data from other procedures and diagnoses with lower and higher mortality rates are also used for illustration. STUDY DESIGN: The computational methods to derive probabilities using the Poisson, normal, simulation, and exact probabilities are discussed. Using a previously developed risk factor model, the probability of observing the actual number of deaths (or more) is calculated given the expectation of death for each patient in each hospital. Results for the four methods are compared, showing the types of random and systematic errors in the Poisson, normal, and simulation approaches. DATA COLLECTION: Routinely collected hospital discharge abstract data were provided by the California Office of Statewide Planning and Development. PRINCIPAL FINDINGS: The Poisson and normal approximations are often biased substantially in calculating upper-tail p-values, especially when the expected number of adverse outcomes is less than five. Simulations allow unbiased calculations, and the degree of random error can be made arbitrarily small given enough trials. Exact calculations using a simple recursive algorithm can be done very efficiently on either a mainframe or personal computer. For example, the whole set of cholecystectomy patients can be assessed in less than 90 seconds on a Macintosh. CONCLUSIONS: Calculating the probability of observing a small number of events using standard approaches may result in substantial errors. The availability of a simple and inexpensive method of calculating these probabilities exactly can avoid these errors.

Bias↗

PubMed1998

The accuracy of patients' judgments of disease probability and test sensitivity and specificity.

BACKGROUND: We studied patients' understanding of the characteristics of diagnostic tests for six common conditions to determine what patients know about diagnostic uncertainties before they communicate with a doctor. We compared the accuracy of patients' estimates of disease probabilities and diagnostic test characteristics for diseases with which they did or did not have prior experience. METHODS: To measure patients' understanding of the uncertainty of diagnostic test results, questionnaires describing diseases were given to patients in clinic waiting rooms. For each of six diseases, a 2-page questionnaire presented a case history of the disease and its diagnostic test, and asked respondents to estimate the probability that the case patient has the suspected disease, the sensitivity of test, the specificity of test, and the probability that the patient has the disease if the test result is positive. It also asked whether the patient, a close friend, or family member had ever been thought to have this disease. RESULTS: One hundred eighty-four patients in the clinic waiting room responded for at least one disease. Although patients judged the disease probabilities to be higher after a positive diagnostic test, each of their four judgments was essentially the same for all diseases, including those with high and low prior probabilities, and with accurate and inaccurate tests. Past experience with the disease was associated with only a minimal increase in the accuracy of patient knowledge. CONCLUSIONS: Patients' ignorance of the uncertainties of diseases demonstrates the need for patient education when a disease is suspected. The lack of relation between knowledge and experience suggests that this need is not being effectively met. To convey the rates or probabilities, and to help the patients understand what the probabilities are based on, a physician should speak in terms that patients can easily understand.

Adolescent↗

PubMed1998

Calculating the exact probability of language-like patterns in biomolecular sequences.

We present algorithms for the exact computation of the probability that a random string of a certain length matches a given regular expression. These algorithms can be used to determine statistical significance in a variety of pattern searches such as motif searches and gene-finding. This work improves upon work of Kleffe and Langebacker (Kleffe & Langbecker 1990) and of Sewell and Durbin (Sewell & Durbin 1995) in several ways. First, in many cases of interest, the algorithms presented here are faster. In addition, the type of pattern considered here strictly includes those of both previous works but also allows, for instance, arbitrary length gaps. Also, the type of probability model which can be used is more general than that of Sewell and Durbin, allowing for Markov chains. The problem solved in this work is in fact in the class of NP-hard problems which are believed to be intractable. However, the problem is fixed-parameter tractable, meaning that it is tractable for small patterns. The is problem is also computationally feasible for many patterns which occur in practice. As a sample application, we consider calculating the statistical significance of most of the PROSITE patterns as in Sewell and Durbin. Whereas their method was only fast enough to exactly compute the probabilities for sequences of length 13 larger than the pattern length, we calculate these probabilities for sequences of up to length 2000. In addition, we calculate most of these probabilities using a first order Markov chain. Most of the PROSITE patterns have high significance at length 2000 under both the i.i.d. and Markov chain models. For further applications, we demonstrate the calculation of the probability of a PROSITE pattern occurring on either strand of a random DNA sequence of up to 500 kilo-bases and the probability of a simple gene model occurring in a random sequence of up to 1 megabase.

Algorithms↗

PubMed1999

Review of 6-month mortality following low-probability lung scans.

BACKGROUND: Ventilation perfusion lung scanning is widely used as a diagnostic method for evaluating patients suspected of having pulmonary embolism (PE). While lung scan interpretation is traditionally performed in terms of probability of PE (usually low, moderate or intermediate, and high), in recent years concern has been raised that the term low probability may be misleading because adverse and even fatal sequelae of PE occasionally occur in such patients. To assess these concerns, a review of mortality in a large series of patients following low-probability lung scans was performed. OBJECTIVE: To determine the 6-month mortality in a consecutive series of patients following low-probability ventilation perfusion (V/Q) lung scans. METHODS: Records of all patients who had low-probability V/Q scans during a 9-year period (1987-1995) were reviewed. Causes of mortality for those patients who died during the 6-month period after the index scan were established from patients' charts, autopsy reports, and computer record data. RESULTS: Of the total 536 evaluable patients, 83 (15%) died within 6 months of the date of the lung scan; 73 (88%) died while inpatients at the Seattle Veterans Affairs Medical Center, Seattle, Wash, and the other 10 (12%) died at other facilities or at home. Pulmonary embolism was not reported as a suspected or probable contributing factor in any of the 83 deaths. Sixty-three patients (76%) who died had a diagnosis of either cancer (n = 32) or advanced cardiovascular disease (n = 31) at the time of their lung scans. Twenty-six patients (31%) underwent autopsies, and PE was not identified on examination of the lungs in any of them. Of the 27 patients who died within 1 month of the scan date, 17 (63%) underwent autopsies. CONCLUSION: Review of data from all patients with low-probability V/Q scans and a follow-up of 6 months showed no documentation to attribute any deaths to PE.

Adult↗

PubMed2003

The probabilities of sex offender re-arrest.

BACKGROUND: Estimates of the probabilities of re-arrest for sex offenders apprehended in Western Australia between April 1984 and December 1994 are reported. POPULATION AND METHOD: Of the 116,151 distinct male persons arrested for the first time from 1984 94, 2785 were identified with at least one sex offence. Subjects on average were followed up for 5.7 years and assessed by criminal record, Aboriginality, bail status, age, occupation and penal intervention. Three criteria, rearrest for any, repeat sex or a violent offence are used to summarize the 'careers' of sex offenders. RESULTS: Overall ultimate probabilities of rearrest for any offence were 0.61, for a repeat sex offence 0.33 and for a violent offence 0.51. Probabilities of re-arrest for non-Aboriginal offenders were lower for all definitions. Younger offenders, Aborigines and those with prior arrest for non-sex offences had higher probabilities for any or violent rearrest but older offenders tended to have higher probabilities of repeat sex offending. Community supervision and imprisonment significantly reduced the 'rate' or speed of re-arrest. DISCUSSION: Actuarial risk assessments for low-probability high-consequence events such as dangerous recidivism are useful for identifying groups with a high probability of rearrest, assisting management of these groups and evaluating penal interventions.

Adolescent↗

PubMed1994

Interaction of oddball probability and primary task type on P300 in the dual-task paradigm.

Using a dual-task paradigm with an oddball secondary task, P300 amplitude and latency were studied as a function of factorially manipulated oddball probability (low = .22, high = .44) and primary task type. In addition to a Baseline condition (oddball task only), three primary tasks were used: (1) Pure Sensory; watching a movie; (2) Pure Motor (manipulating a flashlight); and (3) Sensory/Motor (using the flashlight to trace the outlines of characters in a movie). The findings included the usual significant effects of probability on amplitude. There was also a significant effect of task type on amplitude, and a significant interaction of oddball probability with task type. In the low but not high probability condition, a pure Sensory task depressed P300 amplitude. In both probability conditions, the Sensory/motor task depressed P300 amplitude. Only task type had a significant effect on P300 latency. The results confirm the ability of other labs (using Sensory/motor primary tasks) to demonstrate P300 depression at high oddball probability, in view of the difficulty in our lab of achieving P300 depression with pure sensory tasks and high oddball probabilities. The results are discussed in terms of partial overlap of processing resource pools.

Adult↗

PubMed1990

The estimation of post-test probability of coronary disease following exercise testing using the sequential application of two Bayesian methods.

Recent studies have revealed that Bayesian methods to estimate post-test probability following exercise testing differ in their sensitivity and specificity across the range of post-test probability. To take advantage of the relative strengths of each method, we combined two of these methods into a single method (DUAL BAYES) and compared it with the two original methods in 436 patients who underwent stress testing followed within 2 months by coronary arteriography. All patients had post-test probabilities determined using CADENZA (better sensitivity). Those CADENZA-derived probabilities greater than or equal to 50% were substituted with post-test probabilities determined by Diamond and Forrester's original TABULAR method (better specificity). Mean post-test probabilities were as follows: TABULAR 34, CADENZA 48, DUAL BAYES 37 (actual incidence 38%). Comparison of sensitivity and specificity at every fifth percentile of post-test probability revealed that the sensitivity of DUAL BAYES was better than that of TABULAR and equal to that of CADENZA at thresholds less than or equal to 10 and that the specificity was better than that of CADENZA and equal to that of TABULAR at thresholds greater than or equal to 60. Therefore using both methods as indicated above was better than using either method alone.

Algorithms↗

PubMed1983

Stability and coherence of health experts' upper and lower subjective probabilities about dose-response functions.

As part of a method for assessing health risks associated with primary National Ambient Air Quality Standards. T. B. Feagans and W. F. Biller (Research Triangle Park, North Carolina. EPA Office of Air Quality Planning and Standards, May 1981) developed a technique for encoding experts' subjective probabilities regarding dose--response functions. The encoding technique is based on B. O. Koopman's (Bulletin of the American Mathematical Society, 1940, 46, 763-764; Annals of Mathematics, 1940, 41, 269-292) probability theory, which does not require probabilities to be sharp, but rather allows lower and upper probabilities to be associated with an event. Uncertainty about a dose--response function can be expressed either in terms of the response rate expected at a given concentration or, conversely, in terms of the concentration expected to support a given response rate. Feagans and Biller (1981, cited above) derive the relation between the two conditional probabilities, which is easily extended to upper and lower conditional probabilities. These relations were treated as coherence requirements in an experiment utilizing four ozone and four lead experts as subjects, each providing judgments on two separate occasions. Four subjects strongly satisfied the coherence requirements in both conditions. and three more did no in the second session only. The eighth subject also improved in Session 2. Encoded probabilities were highly correlated between the two sessions, but changed from the first to the second in a manner that improved coherence and reflected greater attention to certain parameters of the dose--response function.

Air Pollution↗

PubMed1989

Calculation of complication probability factors for non-uniform normal tissue irradiation: the effective volume method.

An estimation of normal tissue complication probability factors is important, particularly for evaluating 3-dimensional treatment plans. A method has been developed to calculate complication probability factors for non-uniformly irradiated normal organs using dose volume histograms and complication probabilities for uniform partial organ irradiation. In the effective volume method each volume element of the histogram is considered independently and subject to a power law dose volume relationship. Thus, a non-uniform dose volume histogram is reduced to a uniform one with an effective volume, and a dose equal to the maximum dose to the organ. The complication probability is then obtained from known complication probabilities for uniform partial organ irradiation. The effective volume histogram transformation method is shown to obey various boundary conditions, and is illustrated by comparing probability calculations for alternative 3-dimensional treatment plans for the pelvis. In addition, the limitations of this histogram reduction method are discussed and compared to other calculational techniques. The use of probability factor calculations in treatment plan evaluation, and their role in numerical scoring is explored.

Humans↗

PubMed2004

Probability of introduction of exotic strains of bluetongue virus into the US and into California through importation of infected cattle.

Strategies designed to minimize the probability of bluetongue virus (BTV) introduction to new areas should be based on a quantitative assessment of the probability of actually establishing the virus once it is introduced. The risk of introducing a new strain of bluetongue virus into a region depends on the number of viremic animals that enter and the competency of local vectors to transmit the virus. We used Monte Carlo simulation to model the probability of introducing BTV into California, USA, and the US through importation of cattle. Records of cattle and calf imports into California and the US were obtained, as was seroprevalence information from the exporting countries. A simulation model was constructed to evaluate the probability of importing either a viremic PCR-negative animal after 14-day quarantine, a c-ELISA BTV-antibody-negative animal after 28-day quarantine, or an untested viremic animal after 100-day quarantine into California and into the US. We found that for animals imported to the US, the simulated (best to worst scenarios) median percentage that tested positive for BTV-antibody ranged from 5.4 to 7.2%, while for the subset imported to California, the simulated median percentage that tested positive for BTV-antibody ranged from 20.9 to 78.9%. Using PCR, for animals imported to the US these values were 71.8-85.3%, and for those imported to California, the simulated median that test positive ranged from 74.3 to 92.4%. The probability that an imported animal was BTV-viremic is very low regardless of the scenario selected (median probability=0.0%). The probability of introducing an exotic strain of BTV into California or the US by importing infected cattle was remote, and the current Office International des Epizooties (OIE) recommendation of either a final PCR test performed 14 days after entry into quarantine, a c-ELISA performed 28 days after entry into quarantine or a 100-day quarantine with no testing requirement was adequate to protect cattle in the US and California from an exotic strain of BTV.

Animals↗

PubMed2002

A model of fishing vessel accident probability.

PROBLEM: Commercial fishing is one of the least safe occupations. METHOD: The researchers develop a fishing vessel accident probability model for fishing areas off the northeastern United States using logit regression and daily data from 1981 to 1993. RESULTS: The results indicate that fishing vessel accident probability declined over the study period. Higher wind speed is associated with greater accident probability. Medium-size vessels have the highest accident probability, while small vessels have the lowest. Within the study region, accident probability is lower in the southwestern section than in the northeastern section. Accidents are likely to occur closer to shore than offshore. Accident probability is lowest in spring. IMPACT ON INDUSTRY: The probability model is an important building block in development and quantitative assessment of management mechanisms related to safety in the commercial fishing industry.

Accidents, Occupational↗

PubMed1997

Clinical features of probable moyamoya disease in Japan.

To clarify the current clinical features of probable Moyamoya disease in Japan, 180 cases were analyzed based on the cases collected by the Research Committee on Spontaneous Occlusion of the Circle of Willis of the Ministry of Health and Welfare, Japan. Although the age distribution patterns of probable Moyamoya disease showed two peaks similar to that of definite cases, the pattern shifted to the right thus indicating a reversed children versus adult ratio. The female/male ratio was 1.65, which was not significantly different from that observed in definite cases. The family occurrence rate was 6.7%. The incidence of cerebral infarction and bleeding in probable cases was higher than that in definite cases. The incidence of hemorrhage was higher in females than in males. Angiographically probable cases were at earlier stages in comparison to definite cases. The rebuild-up phenomenon in electroencephalograms was less detectable than in definite cases. Surgical procedures were performed in 63.3% of all cases and approximately 81% of them underwent bypass surgery. Single encephalo-duro-arterio-synangiosis, direct bypass and combined bypass procedures were performed in 35, 40 and 25% of all surgical cases, respectively. Although the incidence of bleeding was higher in the probable cases, the outcomes of the patients were similar to that of the definite cases except for mortality. Approximately 7% of the probable cases developed into definite type within an average 6.6 year follow-up period. The majority of probable Moyamoya disease cases thus seems to have somewhat different clinical characteristics from the definite disease cases.

Adolescent↗

PubMed2000

Off-site ignition probability of flammable gases.

A key step in the assessment of risk for installations where flammable liquids or gases are stored is the estimation of ignition probability. A review of current modelling and data confirmed that ignition probability values used in risk analyses tend to be based on extrapolation of limited incident data or, in many cases, on the judgement of those conducting the safety assessment. Existing models tend to assume that ignition probability is a function of release rate (or flammable gas cloud size) alone and they do not consider location, density or type of ignition source. An alternative mathematical framework for calculating ignition probability is outlined in which the approach used is to model the distribution of likely ignition sources and to calculate ignition probability by considering whether the flammable gas cloud will reach these sources. Data are collated on the properties of ignition sources within three generic land-use types: industrial, urban and rural. These data are then incorporated into a working model for ignition probability in a form capable of being implemented within risk analysis models. The sensitivity of the model results to assumptions made in deriving the ignition source properties is discussed and the model is compared with other available ignition probability methods.

Accidents, Occupational↗

PubMed2004

Phonotactic probabilities in young children's speech production.

This research explores the role of phonotactic probability in two-year-olds' production of coda consonants. Twenty-nine children were asked to repeat CVC non-words that were used as labels for pictures of imaginary animals. The CVC non-words were controlled for their phonotactic probabilities, neighbourhood densities, word-likelihood ratings, and contained the identical coda across low and high phonotactic probability pairs. This allowed for comparisons of children's productions of the same coda consonant in low and high phonotactic probability environments. Children were significantly more likely to produce the same coda in high phonotactic probability non-words than in low phonotactic probability non-words. These results are consistent with the hypothesis that phonotactic probability is a predictor of coda production in English. Moreover, this finding provides further evidence for the role of the input and distribution of sound patterns in the ambient language as a basis for phonological acquisition.

Child, Preschool↗

PubMed2005

Effects of contextual predictability and transitional probability on eye movements during reading.

In 2 eye-movement experiments, the authors tested whether transitional probability (the statistical likelihood that a word precedes or follows another word) affects reading times and whether this occurs independently from contextual predictability effects. Experiment 1 showed early effects of predictability, replicating S. A. McDonald and R. C. Shillcock's (2003a) finding that words with a high transitional probability (defeat following accept) are read faster than words with a low transitional probability (losses following accept). However, further analyses suggested that the transitional probability effect was likely due to differences in predictability rather than transitional probability. Experiment 2, using a better controlled set of items, again showed an effect of predictability, but no effect of transitional probability. The authors conclude that effects of transitional probability are part of regular predictability effects. Their data also show that predictability effects are detectable very early in the eye-movement record and between contexts that are weakly constraining.

Eye Movements↗