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PubMed2003

Using a Rasch scale to characterize the clinical features of patients with a clinical diagnosis of uncertain, probable, or possible Alzheimer disease at intake.

OBJECTIVE: This study examined the clinical features of patients with clinical diagnoses of probable Alzheimer disease (AD), possible AD, and uncertain. DESIGN: Case study comparing three groups of AD patients diagnosed at their initial visit to an Alzheimer outpatient clinic. SETTING: Southern Illinois University School of Medicine's Center for Alzheimer Disease and Related Disorders (CADRD) assessment sites (20) in rural Illinois. PARTICIPANTS: 300 patients assessed at CADRD between January 1, 1994 and July 1, 2000. MEASUREMENTS: Patients were given an extensive clinical battery consisting of physical and neurologic examination, mental status testing including the Mini-Mental State Exam (MMSE), Short Blessed Dementia (SBD) and Blessed Dementia Scale (ADL), medical history evaluation, and laboratory tests. Other data included age at visit, gender, and medical history variables. RESULTS: Mean MMSE, SBD, and ADL scores differed significantly between groups (p's < 0.01). In all three cognitive tests, the uncertain group was the least impaired while the probable AD group was the most impaired. A Rasch model indicated that only the cognitive measures were useful in discriminating between the three diagnostic groups. CONCLUSION: In general, probable AD patients were distinguished from possible AD patients by the severity of their dementia as measured by the MMSE, ADL and SBD as well as Hachinski-Ischemic Score (HIS) scores. A Rasch model did well at predicting group membership based upon dementia measures only. The uncertain group differed from the AD groups in age and dementia severity as measured by the MMSE, ADL and SBD. Noting differences between this and previous studies, we speculate disparity may be related to differences in population ethnicity.

Activities of Daily Living↗

PubMed2003

Probability judgment and subadditivity: the role of working memory capacity and constraining retrieval.

In this research, we examined the role that individual differences in working memory (WM) capacity, the strength of alternatives, and time constraints play in probability judgment and subadditivity. With a laboratory-based learning task, Experiment 1 revealed that the degree to which participants' probability judgments were subadditive was negatively correlated with a measure of WM capacity, even when variance due to short-term memory capacity was removed. In addition, participants were more subadditive when the viable alternatives were all rather weak. Experiment 2 extended the WM-capacity-subadditivity correlation to a population judgment task and revealed that subadditivity increases when the judgment task is performed under time constraints. Results support a model that assumes that people make probability judgments by comparing the focal hypothesis with relevant alternatives retrieved from long-term memory and that people high in WM span include more alternatives in the comparison process. Time constraints are assumed to truncate the alternative generation process, leading to fewer alternatives being recalled from long-term memory.

Humans↗

PubMed1980

[The late positive component (P3) in auditory evoked potentials: effects of probabilities and numbers of stimulus presentation (author's transl)].

Scalp evoked potentials to tone pips were recorded for nine subjects while performing a visual tracking task. The pips, which differed in intensity (40 & 60 dB), were presented as either frequent on infrequent stimuli. These stimuli were randomly presented under three stimulus conditions which were determined in terms of probability (0.10 or 0.40) and number of infrequent stimuli (24 or 96) in one run. It was shown that the amplitude of the P3 wave (around 340 ms latency) in response to the infrequent stimuli was larger for the low probability condition than for the high probability condition, while no effect on the P3 amplitude was found for the numbers of the stimuli.

Adult↗

PubMed2004

Generating pre-test probabilities: a neglected area in clinical decision making.

OBJECTIVE: To assess the accuracy and variability of clinicians' estimates of pre-test probability for three common clinical scenarios. DESIGN: Postal questionnaire survey conducted between April and October 2001 eliciting pre-test probability estimates from scenarios for risk of ischaemic heart disease (IHD), deep vein thrombosis (DVT), and stroke. PARTICIPANTS AND SETTING: Physicians and general practitioners randomly drawn from College membership lists for New South Wales and north-west England. MAIN OUTCOME MEASURES: Agreement with the "correct" estimate (being within 10, 20, 30, or > 30 percentage points of the "correct" estimate derived from validated clinical-decision rules); variability in estimates (median and interquartile ranges of estimates); and association of demographic, practice, or educational factors with accuracy (using linear regression analysis). RESULTS: 819 doctors participated: 310 GPs and 288 physicians in Australia, and 106 GPs and 115 physicians in the UK. Accuracy varied from about 55% of respondents being within 20% of the "correct" risk estimate for the IHD and stroke scenarios to 6.7% for the DVT scenario. Although median estimates varied between the UK and Australian participants, both were similar in accuracy and showed a similarly wide spread of estimates. No demographic, practice, or educational variables substantially predicted accuracy. CONCLUSIONS: Experienced clinicians, in response to the same clinical scenarios, gave a wide range of estimates for pre-test probability. The development and dissemination of clinical decision rules is needed to support decision making by practising clinicians.

Adult↗

PubMed1988

Posttest probability calculation by weights. A simple form of Bayes' theorem.

This article reintroduces a different form of Bayes' theorem that allows calculation of posttest probabilities by adding quantities known as "weights." A weight combines information found in both a test's sensitivity and specificity. A single value can describe how a given test result changes the posttest probability of disease. The use of weights and this form of Bayes' theorem should allow more widespread understanding and use of probability theory in clinical practice.

Bayes Theorem↗

PubMed1976

On the absorption probabilities and absorption times of finite homogeneous birth-death processes.

This paper provides some formulas for the absorption probabilities, the mean absorption times and the variances of first absorption times in finite homogeneous absorbing birth-death processes. The results are then applied to a genetic model of Moran [1958] for computing the absorption probability densities, the mean absorption times and the variances of first absorption times. Specifically, it is shown that the probability distribution of the first absorption time is the matrix analog of exponential distribution or a mixture of exponential distributions if the transition matrix is diagonable.

Alleles↗

PubMed1998

Transition probability cell cycle model with product formation.

A cell cycle population model based on the transition probability model of Smith and Martin (1973) has been extended to include product synthesis and export. The model handles two probable mechanisms. In the direct production model, the product is the protein. In the transcription model, the product is the specific mRNA. The protein is synthesized by translation of the specific mRNA and subsequently exported. In either case, the cell density is jointly distributed in the primary product and maturity age in the cell cycle. This extended model also is capable of describing a large range of conditions, including substrate dependent batch and continuous cultures. With the use of unity maturity-velocity (but the transition rate a function of limiting substrate), the model is shown to exhibit a negative growth association between the specific productivity of monoclonal antibodies from hybridomas and the dilution rates of a chemostat. Possibilities of maturity age dependent transcription and translation are considered, and the results show that these features can amplify the specific productivity negative association with specific growth rate. While this model may provide a partial elucidation of monoclonal antibody productivity in a chemostat, the present work provides a proper framework with which probable cell cycle dependent product formation can be analyzed rigorously with a comprehensive computational model.

Animals↗

PubMed1999

Correlation of miniature synaptic activity and evoked release probability in cultures of cortical neurons.

Spontaneous miniature synaptic activity is caused by action potential (AP)-independent release of transmitter vesicles and is regulated at the level of single synapses. In cultured cortical neurons we have used this spontaneous vesicle turnover to load the styryl dye FM1-43 into synapses with high rates of miniature synaptic activity. Automated selection procedures restricted analysis to synapses with sufficient levels of miniature activity-mediated FM1-43 uptake. After FM1-43 loading, vesicular FM1-43 release in response to AP stimulation was recorded at single synapses as a measure of release probability. We find that synapses with high rates of miniature activity possess significantly enhanced evoked release rates compared with a control population. Because the difference in release rates between the two populations is [Ca(2+)](o)-dependent, it is most likely caused by a difference in release probability. Within the subpopulation of synapses with high miniature activity, we find that the probabilities for miniature and AP-evoked release are correlated at single synaptic sites. Furthermore, the degree of miniature synaptic activity is correlated with the vesicle pool size. These findings suggest that both evoked and miniature vesicular release are regulated in parallel and that the frequency of miniature synaptic activity can be used as an indicator for evoked release efficacy.

Action Potentials↗

PubMed1999

PROBES: a framework for probability elicitation from experts.

A decision analytic model represents uncertainties as probability distributions. These distributions are hard to assess especially for large and dynamic models. We propose an integrated framework that facilitates elicitation of the relevant probability distributions for dynamic decision models from the domain experts. The experts usually use some judgmental heuristics to aid probability assessments; the resulting distributions may be proned to cognitive biases. Our framework aims to minimize the effects of these biases and to improve the quality of decisions made. We have implemented a prototype system of the framework and evaluated its effectiveness via a case study in the follow-up management of colorectal cancer patients after curative surgery. Preliminary results demonstrate the practical promise of the framework.

Colorectal Neoplasms↗

PubMed2000

The effect of marginal tax rate on the probability of employment-based insurance by risk group.

RESEARCH OBJECTIVE: To evaluate the effect of the tax subsidy on participation in employment-based health insurance for high- and low-risk individuals. The total exclusion of employer-paid health insurance premiums from taxable income has frequently been seen as contributing to excess insurance and hence welfare loss. However, less attention has been paid to quantifying the extent to which the tax subsidy mitigates the deleterious effects of adverse selection on the health insurance market. Adverse selection reduces pooling in an insurance market, so that high-risk individuals are either unable to obtain coverage or are forced to pay premiums that are unaffordable to all but the wealthiest. If there is an external benefit to society of an individual's purchase of medical care, then the presence of adverse selection may reduce the purchase of health care below the socially optimal level. Therefore, a mechanism for enhancing access to insurance and ultimately to medical care for high-risk individuals may be socially desirable. STUDY DESIGN: Data from the March 1996-March 1998 Current Population Survey (CPS). For each observation in the sample, state and federal income tax liability is calculated using code based on the ACIR Significant Features of Fiscal Federalism. The probability of having employment-based coverage in either one's own name or as a dependent is evaluated as a function of demographic variables such as age, education, marital status and family size, family income, type of employment, employer size, occupation, location, marginal tax rate, risk group (determined by self-assessed health status), and an interaction between risk group and tax rate. CPS data do not identify individuals who have declined offered coverage. Under alternative models of employer group decision making, the tax subsidy will have an important influence on the employer's decision to offer coverage. If offered, high-risk individuals accept coverage, while some low-risk individuals may decline coverage. PRINCIPAL FINDINGS: For all individuals, the probability of having coverage is an increasing function of the marginal tax rate. Those classified as high-risk because their own or a family member's self-assessed health status is fair or poor are less likely to have coverage than those considered low-risk. The effect of the tax subsidy on insurance coverage is greater for high-risk individuals than for individuals classified as low-risk. CONCLUSIONS: These preliminary results indicate that high-risk individuals benefit from the tax subsidy by increased access to employment-based coverage. Therefore, welfare loss from excess levels of health insurance may be mitigated by welfare gain through expanded access to health insurance and hence to health care for high-risk individuals. IMPLICATIONS FOR POLICY, DELIVERY, OR PRACTICE: Elimination or reduction of the tax exclusion of health insurance premiums may have the unintended consequences of disproportionately reducing the probability of obtaining coverage in the employment-based market for high-risk individuals.

Adolescent↗

PubMed2001

Intermediate probability lung scans (IPLS): retrospective review of 82 cases.

OBJECTIVE: In the light of a reported 30-40% prevalence of pulmonary embolism (PE) in intermediate probability lung scans (IPLS) based on results of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study, we examined the frequency of documented PE in 82 patients with IPLS, the management strategy employed in these patients with regards to additional imaging (e.g. further evaluation with venous sonography or spiral computed tomographic angiography (CTA)), anticoagulation therapy, and subsequent follow-up outcomes. METHOD: Retrospective review of the medical records of 82 patients with intermediate probability ventilation-perfusion (V/Q) lung scans from January 1998 to July 1999. RESULTS: 14.1% of V/Q scans were reported as having an intermediate probability of PE. 72% of IPLS were subject to further evaluation with venous Doppler ultrasound and/or CTA, and 39% of these patients had evidence of thrombo-embolic disease. All patients with imaging evidence of thromboembolic disease were started on anticoagulation therapy. In addition, 19 patients were treated based on clinical judgement. Amongst the 35 patients who were not treated, 17 (49%) were based on clinical findings without further imaging. There was no mortality on follow-up of 28 cases of untreated IPLS. CONCLUSION: The majority of IPLS will have further imaging, out of which over one-third will have thrombo-embolic disease. Approximately half of IPLS cases will receive anticoagulation therapy. No mortality or PE was found on follow-up of patients who were not treated.

Adolescent↗

PubMed1986

Estimating the probability of emigration from individual-specific data: the case of Italy in the early twentieth century.

"This article develops a method for estimating the probability of emigration conditional on the observed characteristics of individuals. In addition, it is shown how to calculate the mean, standard error, and confidence intervals of the conditional probability of emigration given a random sample of emigrants. The technique is illustrated by providing statistically consistent estimates of the probability an Italian would emigrate to the United States in 1901 and 1911, conditional on personal attributes."

Americas↗

PubMed2002

[Axiomatic probability by the poet Abu Ala Al MA'ARRI].

The Arabic poet-philosopher Abu AJa AI Ma'ARRI says a famous verse announcing ten centuries before an axiom of the probability theory: that the probability of fundamental space is equal one; and only the death can prove this equality and all of unpredictable phenomenon of life base a probability lower than one.

Arab World↗

PubMed1999

[Probability models for altitude decompression sickness].

Objective. To study the probability or risk of decompression sickness in high altitude flight and to establish a probability model. Method. Survival analysis technique was used in the analysis of the information about altitude decompression sickness. Result. It was found that the risk of decompression sickness initially increases up to a certain time point, and then decreases because of denitrogenation. The hazard function may describe the characteristics of this pattern in changes of risk. The parameters of probability models for altitude decompression sickness can be estimated by using the maximum likelihood method. Conclusion. Prediction with the survival models based on the logistic distribution is good.

Aerospace Medicine↗

PubMed1976

Lifetime probability of additional births by age and parity for American women, 1935-1968: a new measurement of period fertility.

A new fertility measurement, probability that a woman of specified parity and age will bear a given number of births in her remaining lifetime, is proposed in this article. The measurement is a summary index of a set of age-parity-specific birth probabilities and in a particular case it is conceptually analogous to the total fertility by birth order but free from the influence of the parity distribution. Fertility of American women for the period 1935-1968 was studied by use of such lifetime probabilities. It appears that the trend of fertility of high birth orders has been parallel with that of low orders. Initiation of the recent decline in fertility depends on parity and age of woman.

Adolescent↗

PubMed2003

[Analysis of HLA matching probability in Guangzhou Cord Blood Bank].

The HLA matching results for 1 060 patients searching donors within 3 000 units of umbilical cord blood in Guangzhou Cord Blood Bank from 1998 to 2002 were analyzed. There were 119 (11.23%) and 992 (93.58%) patients found 6/6 and more than 4/6 of HLA matched loci of unrelated cord blood donors respectively. 61.29% of probability in all patients could find one or more cord blood with 4/6 or more matched loci and total nucleated cell (TNC) dose of >or= 3.7 x 10(7)/kg. The highest mean body weight in these supplied patients was 79 kg. The probability was 89.79% for those patients with TNC dose of >or= 2.0 x 10(7)/kg and >or= 4/6 of HLA loci matched. In these patients, the highest weight was 175 kg. In conclusion, a cord blood bank with 3 000 units or more of cord blood in stock shows a high probability of HLA matching and can meet the requirement of TNC >or= 3.7 x 10(7)/kg dose in child and part of adult patients. The umbilical cord blood is a good alternative stem cell source for all patients including adults.

Blood Banks↗

PubMedDate not supplied

Probability of failure of veneered glass fiber-reinforced composites and glass-infiltrated alumina with or without zirconia reinforcement.

PURPOSE: The probability of failure under flexural load of veneered specimens of a unidirectional glass fiber-reinforced composite (FibreKor/Sculpture), a bidirectional glass fiber-reinforced composite (Vectris/Targis), a glass-infiltrated alumina (In-Ceram Alumina/Vita alpha), and a zirconia-reinforced glass-infiltrated alumina (In-Ceram Zirconia/Vita alpha) was investigated; a metal-ceramic (PG200/Vita omega) system served as a control. MATERIALS AND METHODS: Ten uniform beams of the veneered core materials were fabricated for each system and subjected to a three-point bending test. The data were analyzed using the Weibull method. The failure load of specimens at a 10% probability of failure (B10 load) was compared. The mode of failure was analyzed. RESULTS: The B10 load of the systems investigated was not significantly different from that of the metal-ceramic system. FibreKor possessed significantly higher B10 load than Vectris, In-Ceram Alumina, and In-Ceram Zirconia. The B10 strength loads of Vectris, In-Ceram Alumina, and In-Ceram Zirconia were not significantly different from one another. CONCLUSION: The probability of FibreKor to fracture under a flexural load was significantly lower than that of Vectris, In-Ceram Alumina, or In-Ceram Zirconia.

Aluminum Oxide↗

PubMed2004

Cardiovascular risk factors and probability for cardiovascular events in HIV-infected patients - part III: age differences.

OBJECTIVE: In recent years, concerns have been growing about an elevated rate of cardiovascular diseases in HIV-infected patients due to side effects of antiretroviral therapy. The present study analyses the cardiovascular risk profile and the probability of cardiovascular events with regard to the age of HIV-infected patients. METHODS: Cardiovascular risk factors of 309 HIV-infected adults were analysed. Patients were divided into four groups: 18-30 years (group 1), 31-40 years (group 2), 41-50 years (group 3), > 50 years (group 4). Overall 10-years probability for cardiovascular events was evaluated by the Framingham algorithm. RESULTS: Differences between the groups were detected in cardiovascular risk factors including changes in lipid- and glucose metabolism. Lipid values increased with elevated age, such as total cholesterol concentration (Mean +/- SEM in group 1 vs. group 4: 4.71 +/- 0.20 to 6.36 +/- 0.21 mmol/L, p < 0.05), LDL-cholesterol concentration (2.86 +/- 0.17 vs. 4.17 +/- 0.21 mmol/L, p < 0.05) and triglyceride concentration (1.56 +/- 0.14 vs. 3.48 +/- 0.40 mmol/L, p < 0.05). HDL-cholesterol concentration did not show a significant difference (1.15 +/- 0.03 mmol/L). Glucose concentration increased with elevated age in HIV-infected patients (5.28 +/- 0.19 vs. 6.46 +/- 0.24 mmHg, p < 0.05), but there was no significant difference in HbA1c - concentration, blood pressure and smoking rate between the groups. The overall 10-years probability for cardiovascular events was higher in group 1 (median: 1.9%) than in group 4 (20.5%; p < 0.01). CONCLUSIONS: The risk of cardiovascular events is related to the age in HIV-infected patients. Therefore, an increased duration of life due to a more effective antiretroviral therapy will have a significant impact on the rate of cardiovascular events in this patient population. In the future, further increase of cardiovascular events in HIV-infected patients may be expected.

Adolescent↗