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PubMed1993

[Probability of dying in the first year of life in an urban area of southern Brazil].

A birth-cohort of 4,876 children born alive in hospital were selected and followed through up to the age of one year with a view to estimating the risk of dying in the first year of life. All of them were born in 1989, in one of the seven hospitals of an urban area of Southern Brazil and the only requirement for belonging to the cohort was that of residence on the area. The selected variables were: sex, birthweight, age at moment of death, underlying cause of death, and maternal age. The estimated probability of dying in the first year was of 19.9 per 1,000 (77.3% of the deaths occurred during the neonatal period). Perinatal causes and congenital malformations contributed to 80% of the deaths, and infectious diseases were the underlying cause of death in only 1.1% of the losses. The risk of dying in the first year of life due to afections arising during the perinatal period was higher among vaginally delivered babies (20.3 per 1,000) than it was for those born by cesarean section (9 per 1,000). A higher probability of death was present among infants born to adolescent mothers, and those with low birthweight (less than 2,500g). The results brought out the need for improving the quality of prenatal and infant care. They also suggested the hypothesis of a possible association between higher infant mortality and lower socio-economic level.

Age Factors↗

PubMed2005

Projected population-level effects of thiobencarb exposure on the mysid, Americamysis bahia, and extinction probability in a concentration-decay exposure system.

Population-level effects of the mysid, Americamysis bahia, exposed to varying thiobencarb concentrations were estimated using stage-structured matrix models. A deterministic density-independent matrix model estimated the decrease in population growth rate (lambda) with increasing thiobencarb concentration. An elasticity analysis determined that survival of middle stages provided the largest contribution to lambda. Decomposing the effects of lambda in terms of changes in the matrix components determined that reduced reproduction had a large influence on population dynamics at lower thiobencarb concentrations, whereas reduced survivorship had the largest impact on populations at higher concentrations. A simulation model of a concentration-decay system was developed to demonstrate the importance of integrating chemical half-life and management practices in determining population viability. In this model, mysids were originally exposed to a high thiobencarb concentration (300 microg/L) that decayed an order of magnitude in the number of mysid generations corresponding to thiobencarb half-life values under three different exposure regimes. Environmental stochasticity was added to the model to estimate the cumulative extinction probability of mysids exposed to fluctuating concentrations of thiobencarb in random environments. The cumulative extinction probability increased with thiobencarb half-life, stochasticity, and concentration present at the time of a new exposure. The model demonstrated the expansion of population projection models in determining the ecological impact of a population exposed to pesticides.

Animals↗

PubMed2000

Effects of high-probability requests on the latency to initiate academic tasks.

The purpose of this study was to evaluate the effectiveness of a high-probability request sequence on the latency to and duration of compliance to a request for completion of an independent math assignment. The participant was an elementary-school student with learning disabilities who exhibited noncompliance during math instruction. The results showed that high-probability requests were effective in reducing the latency to compliance but only minimally affected duration of engagement.

Adolescent↗

PubMed1964

BEHAVIOR STABILITY AND RESPONSE RATE AS FUNCTIONS OF REINFORCEMENT PROBABILITY ON "RANDOM RATIO" SCHEDULES.

A random ratio schedule is one under which every ordinally specified response has the same probability of reinforcement as any other. Data have been gathered at several values of this type of schedule, using a separate group of pigeons for each schedule value and giving prolonged exposure to each value. No simple relationship was found between response rate and reinforcement probability. In general aspect group data from the present experiment agree with those from a single organism study cited. It was shown that 40 to 50 days of exposure to random ratio schedules yields fairly asymptotic response rate data. The tabulated raw data, and the results of some statistical manipulations, have been deposited with the American Documentation Institute.

Animals↗

PubMed1966

Concurrent schedules of interresponse time reinforcement: probability of reinforcement and the lower bounds of the reinforced interresponse time intervals.

Data were obtained with rats on the effects of interresponse time contingent reinforcement of the lever press response using schedules in which interresponse times falling within either of two temporal intervals could be reinforced. Some of the findings were (a) the mode of the interresponse time distribution generally occurred near the first lower bound when the maximum reinforcement rate for the two lower bounds was equal; this also frequently occurred even when the reinforcement rate was less for the first lower bound; (b) as is the case with schedules using a single interval of reinforced interresponse times the values of the lower bounds partially determined the location and spread of the distributions; but the particular pair of values used did not seem to influence the effects of the probabilities of reinforcement; (c) although the modal interresponse time was usually at the lower bound of one of the two intervals of reinforced interresponse times, no simple relation existed between either the probability or rate of reinforcement of interresponse times in these two intervals and the location of this mode.

Animals↗

PubMed1999

Measuring sensitivity in pharmacoeconomic studies. Refining point sensitivity and range sensitivity by incorporating probability distributions.

OBJECTIVE: The aim of the present study is to describe a refinement of a previously presented method, based on the concept of point sensitivity, to deal with uncertainty in economic studies. DESIGN: The original method was refined by the incorporation of probability distributions which allow a more accurate assessment of the level of uncertainty in the model. In addition, a bootstrap method was used to create a probability distribution for a fixed input variable based on a limited number of data points. The original method was limited in that the sensitivity measurement was based on a uniform distribution of the variables and that the overall sensitivity measure was based on a subjectively chosen range which excludes the impact of values outside the range on the overall sensitivity. PATIENTS AND PARTICIPANTS: The concepts of the refined method were illustrated using a Markov model of depression. MAIN OUTCOME MEASURES AND RESULTS: The application of the refined method substantially changed the ranking of the most sensitive variables compared with the original method. The response rate became the most sensitive variable instead of the 'per diem' for hospitalisation. CONCLUSIONS: The refinement of the original method yields sensitivity outcomes, which greater reflect the real uncertainty in economic studies.

Economics, Pharmaceutical↗

PubMed1985

Lung scan perfusion defects limited to matching pleural effusions: low probability of pulmonary embolism.

Patients with a new pleural effusion are often sent for a ventilation-perfusion scan to exclude a pulmonary embolism. This retrospective study assessed the probability of pulmonary embolism when a pleural effusion and a perfusion defect of similar size are the only significant imaging abnormalities. In 451 reports of patients who were scanned for suspected pulmonary embolism, 53 had perfusion defects secondary to pleural effusion without other significant perfusion defects. Using pulmonary angiography, venography, analysis of pleural fluid, clinical course, and other radiographic and laboratory studies to establish the final diagnosis, only two patients had documented venous thrombotic disease: one had pulmonary emboli, the other thrombophlebitis. Lung scans having significant perfusion defects limited to pleural effusions and matching them in size have a low probability for pulmonary embolism.

Adult↗

PubMed2001

Multilevel performance probability: a meta-analytic integration of expectancy and self-efficacy.

A meta-analysis of one approach to measuring expectancy and self-efficacy was conducted. Although used for over 25 years, this measure has yet to be named or integrated across the two theoretical domains. We proposed to label this measure a Multilevel Performance Probability and conducted a meta-analysis. The search for empirical tests of expectancy and self-efficacy using this procedure yielded 16 studies with ratings which could be subjected to meta-analysis. Five studies with 8 tests were taken from expectancy studies and 11 studies with 47 tests from studies of self-efficacy. In total, the analyses involved 7,444 subjects across 55 tests of the Multilevel Performance Probability to performance relationship. Examination of the measure as a predictor of performance gave a mean r of .51 (p<.001) which is in the same direction and larger than values from other meta-analyses conducted within each of the two theoretical domains (rs of .21 and .38).

Humans↗

PubMed1995

Reliability of the probability effect on event-related potentials during repeated testing.

The reliability of event-related potentials (ERPs) was studied in 10 healthy adults who were tested 8 times over 7-10 day intervals using a standard auditory oddball paradigm. The difference waveforms, obtained by subtracting the averaged waveforms for frequent trials from those obtained in rare trials, were designed to analyze the components of the ERPs, such as the P300, and to focus on the reliability of the probability effect on the ERPs. The between-session reliability (8 sessions) and the within-session reliability (order of blocks or of different visual procedures) were computed for the obtained difference waveforms. The between-session reliabilities, expressed as the intraclass correlations (r') for the P300 amplitude, area and latency, were 0.70, 0.61 and 0.65, respectively. The within-session reliability, presented as the Pearson correlation coefficients (r) for the three P300 measures were 0.43, 0.35 and 0.25 for different eyes. The values were 0.45, 0.39, 0.42 between the first and the second blocks (eyes-open) and 0.58, 0.47 and 0.29 (eyes-closed). These findings indicate that the P300 amplitude calculated from the difference waveforms may be the most stable marker for the between-session reliabilities. There were no significant differences in the P300 measures over the 8 sessions, suggesting that habituation may not occur with the difference waveform reflecting the probability effect on ERPs. The difference waveform may be useful in research on repetitive group ERPs.

Adult↗

PubMed2003

Data selection and natural sampling: probabilities do matter.

Probabilistic accounts of Wason's selection task (Oaksford & Chater, 1994, 1996) are controversial, with some researchers failing to replicate the predicted effects of probability manipulations. This paper reports a single experiment in which participants sampled the data naturally-that is, sequentially. The proportions of possible data types (i.e., cards in the selection task) also reflected the probability manipulation. Other than this procedural difference, the materials were the same as those in Oberauer, Wilhelm, and Rosas-Diaz's (1999) Experiment 3, which failed to show probabilistic effects. Significant probabilistic effects were observed. Moreover, in a comparative model-fitting exercise, a revised version of the information gain model (Hattori, 1999, 2002; Oaksford & Chater, in press-b) was shown to provide better fits to these data than did competing explanations.

Choice Behavior↗

PubMed2004

Missing information in multiple-cue probability learning.

In a multiple-cue probability learning task, participants learned to use six discrete symptoms (i.e., cues) to diagnose which of three possible flu strains a hypothetical patient suffered from. For some patients, information regarding the status of certain symptoms was not available. Various possible ways in which the missing cue information might be processed were distinguished and tested in a series of three experiments (Ns = 80, 109, and 61). The results suggest that the judged probability of the outcome variable (i.e., flu strain) was assessed by "filling in" the missing cue information with a mean value based on previous observations. The predictions of other methods of processing missing cue information are inconsistent with the data.

Cues↗

PubMed1999

MPROB: computation of multinomial probabilities.

An algorithm for computing exact multinomial probabilities is presented that uses the fewest number of operations that are possible without symbolic simplification of the multinomial coefficient and performs them in a sequence that minimizes the potential for overflow or underflow errors. Multinomial probabilities computed with this algorithm are accurate to machine precision, unlike those based on logarithmic transformations and/or the evaluation of factorials, using Stirling's approximation.

Algorithms↗

PubMed1999

Generating fixed-length sequences satisfying any given nth-order transition probability matrix.

An experimental design involving sequences of m distinct events can be conceptualized as an nth-order transition probability matrix specifying the probabilities with which each of the m distinct events is to follow certain n-grams. This paper describes a general method for constructing sequences of shortest possible length that satisfy any such matrix and presents a computer program that randomly generates such sequences.

Algorithms↗

PubMed1989

Instructional and probability manipulations of bias in multiletter matching.

Ratcliff (1985) performed fits of his diffusion model to the results of multiletter-matching experiments conducted by Ratcliff and Hacker (1981) and Proctor, Rao, and Hurst (1984), in which bias to respond "same" or "different" was manipulated by instructions and probabilities, respectively. The fits showed that both bias manipulations affected settings of a goodness-of-match criterion, whereas instructions also affected sensitivity. Evaluations of the experimental procedures and of Ratcliff's model-fitting procedures were performed in the present study. Three experiments showed that instructions and probabilities had similar effects, regardless of whether the different pairs were blocked or randomized according to the number of mismatching positions. The most salient feature of the results--that "same" reaction times were traded off more than were "different" reaction times, with no corresponding asymmetry in the error rates--was evident in all situations. The evaluation of Ratcliff's model-fitting procedures indicated that the apparent influence of instructions on sensitivity likely is an artifact of unequal variance for the sets of same and different pairs. Moreover, the effects of bias can be explained in terms of settings of response criteria, rather than of the goodness-of-match criterion, as in Ratcliff's fits.

Adult↗

PubMed2000

The boundary for growth of Zygosaccharomyces bailii in acidified products described by models for time to growth and probability of growth.

Models to predict days to growth and probability of growth of Zygosaccharomyces bailii in high-acid foods were developed, and the equations are presented here. The models were constructed from measurements of growth of Z. bailii using automated turbidimetry over a 29-day period at various pH, NaCl, fructose, and acetic acid levels. Statistical analyses were carried out using Statistical Analysis Systems LIFEREG procedures, and the data were fitted to log-logistic models. Model 1 predicts days to growth based on two factors, combined molar concentration of salt plus sugar and undissociated acetic acid. This model allows a growth/no-growth boundary to be visualized. The boundary is comparable with that established by G. Tuynenburg Muys (Process Biochem. 6:25-28, 1971), which still forms the basis of industry assumptions about the stability of acidic foods. Model 2 predicts days to growth based on the four independent factors of salt, sugar, acetic acid, and pH levels and is, therefore, much more useful for product development. Validation data derived from challenge studies in retail products from the U.S. market are presented for Model 2, showing that the model gives reliable, fail-safe predictions and is suitable for use in predicting growth responses of Z. bailii in high-acid foods. Model 3 predicts probability of growth of Z. bailii in 29 days. This model is most useful for spoilage risk assessment. All three models showed good agreement between predictions and observed values for the underlying data.

Food Microbiology↗

PubMed1997

[The effects of judge's roles on probability judgment].

A number of studies on probability judgment have reported that people often tend to neglect the base-rate in the Cab Problem (Bar-Hillel, 1980). To explain the base-rate neglect, the present research hypothesized that subjects presented with the Cab Problem focused on the case information in the problem, because the subjects were asked to estimate probability based on that particular case. In 'two experiments, subjects' individuated or general interpretation of the Cab Problem was manipulated by instructing the subjects to play either responsible or neutral judge's role, respectively. The results suggested that in the responsible judge condition the case information had large impact on subjects' judgment, whereas in the neutral judge condition it did not. These results implied that the subject's base-rate neglect arose from taking the individuated interpretation.

Adult↗

PubMed1985

Diagnostic tests in breast cancer. Clinical strategies based on diagnostic probabilities.

Optimal diagnostic strategies used in screening for breast cancer and evaluating breast masses depend on the likelihood of malignancy, findings at physical examination, and the accuracy of tests and procedures. Results from published series, in conjunction with calculations of the probability of malignancy based on test results, indicate that only mammography is needed for screening. A clinical sequence for evaluating palpable breast masses should include a combination of mammography, ultrasound examination, and needle aspiration. In patients with negative findings, the probability of cancer will be sufficiently low to obviate the need for immediate surgical biopsy. However, if there are positive findings, or the initial clinical likelihood of malignancy is high, excision of the mass is indicated.

Adult↗

PubMed1983

Clinical trials and statistical verdicts: probable grounds for appeal.

Conventional interpretation of clinical trials relies heavily on the classic p value. The p value, however, represents only a false-positive rate, and does not tell the probability that the investigator's hypothesis is correct, given his observations. This more relevant posterior probability can be quantified by an extension of Bayes' theorem to the analysis of statistical tests, in a manner similar to that already widely used for diagnostic tests. Reanalysis of several published clinical trials according to Bayes' theorem shows several important limitations of classic statistical analysis. Classic analysis is most misleading when the hypothesis in question is already unlikely to be true, when the baseline event rate is low, or when the observed differences are small. In such cases, false-positive and false-negative conclusions occur frequently, even when the study is large, when interpretation is based solely on the p value. These errors can be minimized if revised policies for analysis and reporting of clinical trials are adopted that overcome the known limitations of classic statistical theory with applicable bayesian conventions.

Aspirin↗