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Results for “Bayesian analysis”

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PubMed1991

The evaluation of patients with human immunodeficiency virus-related disorders and brain mass lesions.

In patients at risk for acquired immunodeficiency syndrome who present with a mass lesion, a dilemma arises as to whether to treat empirically for toxoplasmosis or perform a brain biopsy. We present data that further define the indications for performing brain biopsy vs empiric treatment. We reviewed charts on 59 patients with acquired immunodeficiency syndrome--related disorders and cerebral mass lesions. Thirty-two patients met diagnostic criteria for toxoplasmosis. Bayesian analysis demonstrated that the prior probability of toxoplasmosis was increased by the presence of contrast enhancement on computed tomographic scans (0.68) and toxoplasmosis titers greater than 1:64 (0.81). Features associated with decreasing probabilities of toxoplasmosis included the absence of contrast enhancement on computed tomographic scans (0.29) and toxoplasmosis titers less than or equal to 1:64 (0.14). Ten percent of patients had complications of brain biopsy. Treatment with pyrimethamine and sulfadiazine produced complications in 29% and serious complications in 8% of treated patients. These data favor empiric therapy for patients with typical features of toxoplasmosis and brain biopsy for defined subsets of patients with atypical features.

Bayes Theorem↗

PubMedDate not supplied

[Detection of young female carriers of Duchenne muscular dystrophy].

36 females aged through 1 to 16 years were studied. They were sisters or close kin, on the maternal side, of patients with Duchenne's Muscular Dystrophy (DMD). 23 healthy controls were also studied so as to evaluate the usefulness of determining serum creatine phosphokinase (CPK) as means for detecting young carriers of DMD. 18 of 36 girls (50%) who were the daughters of the affected families, showed CPK seric values more than twice the standard deviation of the mean of the witness group (21 +/- 7.9 U/L). The Bayesian analysis performed on the problem group showed a good correspondence. These findings imply a high range of detection in possible carriers under 16 years of age. We believe that the absence of symptomatology in some of these girls does not eliminate the possibility of being a carrier.

Adolescent↗

PubMedDate not supplied

Improving the sensitivity of cervical cytologic screening. A comparison of duplicate smears and colposcopic examination of patients with cytologic inflammatory epithelial changes.

During a ten-month period, 264 cervical cytologic specimens were submitted in duplicate to two separate cytology laboratories. An attempt was made to perform colposcopy on all 45 patients reported as having an abnormality by either laboratory. All but one patient with a cytologic diagnosis of cervical intraepithelial neoplasia (CIN) underwent colposcopy, as did 68% of the patients with a diagnosis of nondysplastic atypia (inflammatory epithelial changes [IEC]). Five cases of histologically verified CIN were found by colposcopic study of patients with a cytologic diagnosis of CIN; two additional cases were found by colposcopic study of patients with a cytologic diagnosis of IEC. On the assumption that patients not colposcoped were not systematically different from the others with IEC, the screening sensitivities for both laboratories and for cytology followed by colposcopy of IEC cases were estimated. A statistically significant improvement in screening sensitivity was achieved by colposcopic examination of patients with IEC. This conclusion was tempered by a Bayesian analysis that suggested that some of the apparent improved sensitivity could be due to falsely positive biopsy reports. Despite potential benefits, it is premature to recommend universal colposcopic examination of patients with cytologic reports of inflammatory epithelial changes.

Cervix Uteri↗

PubMed1986

Early detection of necrotizing pancreatitis by computer.

In 59 patients admitted with a clinical picture compatible with acute pancreatitis, 88 features, recorded within the first day, were retrospectively collected and stored in a database programmed on a NCR DM V personal computer. On the basis of the final diagnosis, the patients were divided into two groups, according to Becker's grading of acute pancreatitis. A third group comprised the false-positives. Using 14 significant differences (p less than 0.025) between the three groups, a Bayesian analysis was programmed for early prediction, in terms of percentage probability, of each of the three final diagnoses. A retrospective assessment of computer performance was carried out in the patients entered the initial database, and further 38 underwent a prospective test. In the detection of necrotizing pancreatitis the procedure gave 95.8% accuracy, 91.9% sensitivity and 98.3% specificity. Previous diagnosis of pancreatitis, estimate of the degree of necrosis, data to be used for the processing, are discussed. Performances, similar in retrospective and prospective series, proved higher as compared to diagnostic peritoneal lavage. Comparison with Ranson's multiple criteria or computed tomography is inappropriate. The system seems to be reliable feasible and adaptable. The choice of treatment is difficult in acute pancreatitis. A computer-aided analysis may provide a better approach, than an unaided clinical estimate, to several decisional problems in acute pancreatitis.

Acute Disease↗

PubMed1978

The predictive value of myocardial perfusion scintigraphy after stress in patients without previous myocardial infarction.

Seventy-five patients who had chest pain but no history or ECG evidence of myocardial infarction (MI) underwent myocardial-stress perfusion scintigraphy (MSPS) with thallium-201, treadmill-stress testing (TST), and coronary cineangiography (CA). The sensitivities of MSPS and TST for coronary stenosis greater than or equal to 75% were 68% and 71%, respectively; their specificities were 97% and 79%, respectively (0.1 greater than p greater than 0.05). When the character of a patient's chest pain is considered, Bayesian analysis leads to the following conclusions: (a) MSPS can be useful in pre-CA screening of patients with chest pain but no MI if their pain is thought to be of uncertain or nonischemic origin: (b) the sensitivity of Tl-201 MSPS is not sufficient for pre-CA screening of patients without MI who have typical or atypical angina pectoris; (c) the sensitivity of MSPS would have to be approximately 95% in order for the test to be useful in pre-CA screening of patients who have atypical angina pectoris; (d) MSPS may be superior to TST in these applications; and (e) it is not clear that there is any advantage in combining MSPS and TST into a single screening test rather than using MSPS alone.

Cineangiography↗

PubMed1982

[Cytochemical studies of bone marrow plasma cells in monoclonal gammapathies (author's transl)].

Three plasma cell enzymatic reactions--ATPase, acid phosphatase (AP), alpha-naphthyl acetate esterase (alpha-NAE)--were tested in a large number of bone marrow samples from patients with multiple myeloma (MM), benign monoclonal gammapathy (BMG)--idiopathic (iBMG) and secondary (sBMG)--, polyclonal hypergammaglobulinemia (PH), Waldenström's macroglobulinemia (WM) and from normoglobulinemic subjects (NS). The purpose of the present study was to evaluate the significance of these reactions in differential diagnosis of BMG and initial or atypical MM. For each reaction results were expressed as scores and normal limits were statistically established. Our findings in MM, HP and NS are consistent with previous reports (similar enzymatic pattern in NS and PH; depressed ATPase activity, raised AP and alpha-NAE activities in most MM cases). In the BMG class, ATPase activity was normal in about 40% of iBMG, while it was depressed in other cases; most sBMG had diminished ATPase activity. AP patterns were normal for both BMG groups. alpha-NAE activity was normal in 50% of iBMG, while it was raised in the other cases. All the reactions were normal in WM. In a bayesian analysis of cytochemical patterns of NS and MM subjects ATPase showed the highest diagnostic significance, followed by alpha-NAE and AP. ATPase, therefore, seems to be the most useful criterion for the diagnosis of initial MM; low ATPase score BMG patients should therefore be carefully followed-up.

Acid Phosphatase↗

PubMed1982

The noninvasive evaluation of the coronary artery disease patient: clinical, economic and social issues.

The patient with chest pain is a common but often challenging diagnostic problem to the physician. Evaluating such a patient for coronary artery disease requires a careful history, physical examination and judicious selection of laboratory procedures. Noninvasive stress tests for cardiac diagnosis need not be applied to every patient who presents with chest pain and, in general, are most likely to be helpful when they are used discriminately for patients who have an intermediate likelihood of coronary artery disease. A further elaboration of one systematic approach to this problem, based on Bayesian analysis of noninvasive testing procedures, is presented.

Aged↗

PubMed1995

Stopping a clinical trial very early based on unplanned interim analyses: a group sequential approach.

In the conduct of a clinical trial, unexpectedly high rates of toxicity may cause a researcher to want to terminate the trial early even though no formal stopping rule had been specified. The experience of one such clinical trial is used as an example of the ways in which group sequential methodology can be applied in deciding to stop the study, as well as in reporting the results of the clinical trial. This approach is then compared to a Bayesian analysis.

Antidotes↗

PubMed1994

The design of oral sustained-release theophylline dosing after conversion from intravenous to oral therapy.

We studied the design of oral sustained-release theophylline dosing after conversion from constant aminophylline infusion. Twelve children with bronchial asthma (9 boys and 3 girls) were evaluated in this study. Each patient received a constant intravenous administration of aminophylline for 4-10 days. Three hours after conversion from constant aminophylline infusion, they received oral sustained-release theophylline twice daily at 12-hour intervals. Blood samples were obtained at least once during the aminophylline infusion, just before conversion from the aminophylline infusion, and 0, 3 and 6 hours, and 4-5 days after administering oral theophylline. Pharmacokinetic parameters were estimated using the serum theophylline concentrations that were obtained during constant aminophylline infusion. These estimates of pharmacokinetic parameters were used to predict the serum theophylline concentrations during oral theophylline therapy. Predicted serum theophylline concentrations using individual pharmacokinetic parameters were fitted with actual measured values in this study. When switching a patient from intravenous aminophylline to sustained-release oral theophylline, the use of Bayesian analysis of serum theophylline concentration values obtained during intravenous therapy works well in predicting serum theophylline concentrations and in determining oral dosages that maximize the drug's effectiveness.

Administration, Oral↗

PubMed1994

Vancomycin pharmacokinetics in middle-aged and elderly men.

A study was conducted to establish new values for vancomycin volume of distribution (V) and clearance (CL) that would result in more accurate predictions of serum vancomycin concentrations (SVCs). All patients who had received vancomycin at a Veterans Affairs medical center were divided into two groups: those for whom SVCs had been measured between August 13, 1990, and February 12, 1991 (group 1), and those for whom SVCs had been measured between February 13, 1991, and October 4, 1991 (group 2). Data for group 1 were used to derive new values for V and CL by means of Bayesian analysis. SVCs for each patient in group 2 were calculated by using the new pharmacokinetic values, and the predictive performance of these values was compared with that of accepted population values (V = 0.70 L/kg, CL = 0.65 times creatinine clearance [CLcr]). Forty-four men with 95 SVCs were entered into group 1, and 69 men with 171 SVCs were entered into group 2. The mean +/- S.D. ages for groups 1 and 2 were 61.6 +/- 12.9 and 64.3 +/- 11.3 years, respectively. There were no significant differences between the groups. V could not be evaluated because of inadequate sample size. Compared with the method employing the conventional CL value, the method that assumed a CL of 0.90CLcr was more precise and less biased in estimating group 2 SVCs. In middle-aged and elderly men, use of a CL value of 0.90CLcr produced estimates of serum vancomycin concentration that were more precise and less biased than did use of a CL value of 0.65CLcr.

Aged↗

PubMed1994

[Bronchial hyperreactivity in 1994, a cheerful quinquagenarian. Conclusions].

A review is made of the principal themes that are discussed in this supplement of the Revue des Maladies Respiratoires. Three important questions on bronchial hyperresponsiveness, a key feature of asthma, are raised: 1) the clinical usefulness of its assessment, mostly in the atypical forms of asthma and in occupational asthma and, less so, to estimate the severity of asthma; data derived from the Bayesian analysis lead to the conclusion that it is a test which is better for excluding rather than for confirming asthma; in an epidemiological setting, the assessment of bronchial responsiveness should be carried out to assess both host factors and the effect of environmental exposure; 2) the method of assessment which should take into account the stimulus, be it pharmacological or not, the physiological index used to assess the response and the mode of expression of results; 3) finally, the mechanisms of bronchial responsiveness are probably multiple as examined in different chapters of this supplement.

Asthma↗

PubMed1993

Fine needle aspiration in the clinical management of mammary masses.

The role of fine needle aspiration (FNA) for clinical decision-making in patients with nodules of the breast remains in evolution. We retrospectively studied FNA outcomes in 183 patients, stratified by decades of age, to determine the reliability of FNA cytologic examination. Using Bayesian analysis, the predictive value of a positive FNA for women more than 60 years of age is 98 to 99 percent. In women 41 to 60 years of age, those with a first-degree relative with carcinoma of the breast and those with a prior biopsy with increased risk have an 88 to 95 percent likelihood of carcinoma. In women younger than 41 years of age, this likelihood decreases to 65 percent. Additionally, the probability of a lump being carcinoma, given the FNA was negative, ranges from 3 to 80 percent. Therefore, biopsy of a dominant nodule should not be deferred based only on a negative FNA. We can conclude that women 61 years of age or older could be counseled for definitive care at the first operation. Women 41 to 60 years of age, those with a positive family history or those with a past biopsy with increased risk, could be counseled for definitive therapy, but have the diagnosis confirmed with frozen section. Women less than 40 years of age without other risk factors receive no diagnostic benefit from FNA and should only be evaluated with open biopsy.

Adult↗

PubMed1997

[Evaluation of the diagnostic usefulness of CA125 immunoscintigraphy for ovarian carcinoma follow-up after treatment: contribution of this technique in Grenoble University Medical Center].

Immunoscintigraphy using indium-111-labeled OC125 monoclonal antibody F(ab')2 fragments is a technic complementary of morphological imaging (i.e. ultrasonography and computed tomography). It allows early detection of recurrences of ovarian carcinomas. We performed immunoscintigraphy 30 times in 26 patients who previously underwent radical treatment for ovarian carcinoma, and were suspected to have a recurrence. Our purposes were appreciation of diagnostic accuracy of the method, and above all its impact on clinical decisions and evolution of the patients. There were, after reevaluation of the results, 18 true positives, 7 true negatives, 3 false negatives and 2 false positive cases (sensitivity 85.7%, specificity 77.8%). Bayesian analysis showed positive and negative predictive values of 86% and 87% when probability of recurrence a priori was 50%, and 80% and 58% when probability of recurrence a priori was 70%. The result of immunoscintigraphy contributed to clinical decisions in 24 cases out of 30, and led to a correct decision for the patient in 21 cases. Conversely, for the 6 cases in which the result has not been considered, to take this result into account would have been beneficial in 4 cases, but harmful in 2. Finally, survival tended to be longer when immunoscintigraphy was negative, which could be associated with a better prognosis. We conclude that OC125-immunoscintigraphy may be useful for ovarian carcinoma follow-up and may contribute to a better therapeutic strategy.

Adenocarcinoma↗

PubMed1996

Risk-based environmental remediation: Bayesian Monte Carlo analysis and the expected value of sample information.

A methodology that simulates outcomes from future data collection programs, utilizes Bayesian Monte Carlo analysis to predict the resulting reduction in uncertainty in an environmental fate-and-transport model, and estimates the expected value of this reduction in uncertainty to a risk-based environmental remediation decision is illustrated considering polychlorinated biphenyl (PCB) sediment contamination and uptake by winter flounder in New Bedford Harbor, MA. The expected value of sample information (EVSI), the difference between the expected loss of the optimal decision based on the prior uncertainty analysis and the expected loss of the optimal decision from an updated information state, is calculated for several sampling plan. For the illustrative application we have posed, the EVSI for a sampling plan of two data points is $9.4 million, for five data points is $10.4 million, and for ten data points is $11.5 million. The EVSI for sampling plans involving larger numbers of data points is bounded by the expected value of perfect information, $15.6 million. A sensitivity analysis is conducted to examine the effect of selected model structure and parametric assumptions on the optimal decision and the EVSI. The optimal decision (total area to be dredged) is sensitive to the assumption of linearity between PCB sediment concentration and flounder PCB body burden and to the assumed relationship between area dredged and the harbor-wide average sediment PCB concentration; these assumptions also have a moderate impact on the computed EVSI. The EVSI is most sensitive to the unit cost of remediation and rather insensitive to the penalty cost associated with under-remediation.

Animals↗

PubMed2004

Ultraviolet light inactivation of protozoa in drinking water: a Bayesian meta-analysis.

To assess the dose of UV light needed to achieve specified levels of Giardia spp. cysts and Cryptosporidium spp. oocysts inactivation in drinking water, a Bayesian meta-analysis is used to analyze experimental data from several studies. Of the 20 studies identified by an extensive data collection effort, 14 (five reported experiments on Giardia and nine on Cryptosporidium) were selected for analysis based on a set of criteria. A substantial amount of the log inactivation data are reported as greater than a given inactivation level (i.e., censored data). The Bayesian hierarchical modeling approach used in this study not only properly addresses the common concerns in a meta-analysis but also provides a robust method for incorporating censored data. Different statistical models will result in different estimates of the UV doses needed to achieve a specific inactivation level. The Bayesian approach allows us to present the uncertainty in terms of risk, which is better suited for supporting US EPA in developing regulations.

Animals↗

PubMed2001

Bayesian methods of analysis for cluster randomized trials with binary outcome data.

We explore the potential of Bayesian hierarchical modelling for the analysis of cluster randomized trials with binary outcome data, and apply the methods to a trial randomized by general practice. An approximate relationship is derived between the intracluster correlation coefficient (ICC) and the between-cluster variance used in a hierarchical logistic regression model. By constructing an informative prior for the ICC on the basis of available information, we are thus able implicitly to specify an informative prior for the between-cluster variance. The approach also provides us with a credible interval for the ICC for binary outcome data. Several approaches to constructing informative priors from empirical ICC values are described. We investigate the sensitivity of results to the prior specified and find that the estimate of intervention effect changes very little in this data set, while its interval estimate is more sensitive. The Bayesian approach allows us to assume distributions other than normality for the random effects used to model the clustering. This enables us to gain insight into the robustness of our parameter estimates to the classical normality assumption. In a model with a more complex variance structure, Bayesian methods can provide credible intervals for a difference between two variance components, in order for example to investigate whether the effect of intervention varies across clusters. We compare our results with those obtained from classical estimation, discuss the relative merits of the Bayesian framework, and conclude that the flexibility of the Bayesian approach offers some substantial advantages, although selection of prior distributions is not straightforward.

Bayes Theorem↗

PubMed2006

Improving source detection and separation in a spatiotemporal Bayesian inference dipole analysis.

Most existing spatiotemporal multi-dipole approaches for MEG/EEG source localization assume that the dipoles are active for the full time range being analysed. If the actual time range of activity of sources is significantly shorter than the time range being analysed, the detectability, localization and time-course determination of such sources may be adversely affected, especially for weak sources. In order to improve detectability and reconstruction of such sources, it is natural to add active time range information (starting time point and ending time point of source activation) for each candidate source as unknown parameters in the analysis. However, this adds additional nonlinear free parameters that could burden the analysis and could be unfeasible for some methods. Recently, we described a spatiotemporal Bayesian inference multi-dipole analysis for the MEG/EEG inverse problem. This approach treated the number of dipoles as a free parameter, produced realistic uncertainty estimates using a Markov chain Monte Carlo numerical sampling of the posterior distribution and included a method to reduce the unwanted effects of local minima. In this paper, our spatiotemporal Bayesian inference multi-dipole analysis is extended to incorporate active time range parameters of starting and stopping time points. The properties of this analysis in comparison to the previous one without active time range parameters are demonstrated through extensive studies using both simulated and empirical MEG data.

Action Potentials↗

PubMed1996

Measurement of pulsatile flow using MRI and a Bayesian technique of probability analysis.

This work shows that complete spatial information of periodic pulsatile fluid flows can be rapidly obtained by Bayesian probability analysis of flow encoded magnetic resonance imaging data. These data were acquired as a set of two-dimensional images (complete two-dimensional sampling of k-space or reciprocal position space) but with a sparse (six point) and nonuniform sampling of q-space or reciprocal displacement space. This approach enables more precise calculation of fluid velocity to be achieved than by conventional two q-sample phase encoding of velocities, without the significant time disadvantage associated with the complete flow measurement required for Fourier velocity imaging. For experimental comparison with the Bayesian analysis applied to nonuniformly sampled q-space data, a Fourier velocity imaging technique was used with one-dimensional spatial encoding within a selected slice and a uniform sampling of q-space using 64 values of the pulsed gradients to encode fluid flow. Because the pulsatile flows were axially symmetric within the resolution of the experiment, the radial variation of fluid velocity, in the direction of the pulsed gradients, was reconstructed from one-dimensional spatial projections of the velocity by exploiting the central slice theorem. Data were analysed for internal consistency using linearised flow theories. The results show that nonuniform q-space sampling followed by Bayesian probability analysis is at least as accurate as the combined uniform q-space sampling with Fourier velocity imaging and projection reconstruction method. Both techniques give smaller errors than a two-point sampling of q-space (the conventional flow encoding experiment).

Bayes Theorem↗