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PubMed1984

[Calculation of Steel's cell loss factor and of the cellular kinetic parameters for a population with an exponential growth of the cell number and an equal probability of cell death in all phases of the life cycle].

A method of calculation of parameter m (equal to a doubled probability of birth of cells which did not pass into phase G0 from the mitotic cycle) and of the proliferative pool was shown to be the same for the exponential growth phase of cell population with the equal probability of cell death (lambda = const) at all phases of the life cycle (the Steel model of type E), and for the case "lambda = 0" (the Steel model of type B). The method is proposed for the calculation of parameter lambda and of the Steel cell lose factor phi = lambda/[lambda + [ln 2)/tD)]. It is noted that the value of parameter phi for the type E model can be estimated by the Steel formula: phi congruent to 1-tDpot/tD--where tD is the doubling time of the cell number, and tDpot = tcln 2/ln m. Here tc is the mean mitotic cycle duration.

Cell Count↗

PubMed1984

Conditional probability of multiple coronary graft failure.

To assess the potential capability of using artery-specific factors to predict the success of coronary bypass grafting, we classified each graft according to the type of graft (mammary, single vein, or multiple skip vein), the degree of obstruction in the native coronary artery, and the size of the grafted artery. The mean patency rates for each category of graft were determined by performing early postoperative (mean 6.6 months) arteriograms in 354 patients. We found that mammary arteries gave the best results for every graft category. Skip vein grafts had a higher mean patency rate than single vein grafts for arteries with obstructions between 70% and 90% and lumina less than 2.0 mm in diameter. The results for vein and skip grafts were equivalent for the category with arteries greater than 2.0 mm and obstruction greater than 90%. Vein grafts produced better results than skip grafts for the remaining categories. Patients were classified into subgroups according to the number of actually observed graft failures. The probabilities that specific numbers of grafts would fail were calculated for each patient. These probabilities were based upon the observed patency rates for the category appropriate for each graft and the hypothesis that individual grafts within a patient fail independently. We observed an excess number of patients with no failures or multiple failures than would be expected according to the hypothesis of independent failure and category-specific patency rates. Conversely, there were fewer patients than expected who had single failures. Therefore, we postulate that there may also be global factors which influence early graft patency.

Computers↗

PubMed1984

Clinical inferences and decisions--II. Decision trees, receiver operator curves and subjective probability.

In patient management, clinical decisions follow a logical sequence which can be formally expressed as a decision tree in which the uncertainties associated with each alternative outcome may be made explicit using Bayes' theorem. Where test data is used in the formulation of a decision, the uncertainty associated with the information it conveys may be modified by changing the pass/fail criterion to alter the false positive and false negative error rate. Classical procedures based on information theory are described to illustrate how this may be achieved for any test. When hard data is not available to permit such an approach, the clinician must rely on his own past experience or that of a colleague. Several methods are available for quantifying such experience by estimating subjective probabilities associated with an action or test result. Two simple methods are described for deriving subjective probabilities for subsequent use within a Bayesian decision model.

Bayes Theorem↗

PubMed1982

Computation of preoperative diagnosis probability for follicular adenoma and carcinoma of the thyroid on aspiration smears.

Morphometric analysis of 23 follicular tumors (13 adenomas and 10 carcinomas) and 10 metastatic lesions from follicular thyroid carcinomas resulted in the identification of five significant parameters between the carcinoma and adenoma groups. With a classification rule using these features, the probability of a histologic diagnosis of adenoma versus carcinoma was computed for each case. Using threshold values of probabilities of 0.25 and 0.75, only 1 of the 33 cases was not correctly classified on the cytologic smear alone; the remaining 32 cases were correctly classified. These results indicate that morphometric analysis in follicular tumors of the thyroid may be of great help in individual patient care if used as a selective method by a well-trained cytopathologist.

Adenocarcinoma↗

PubMed1982

Predicting the probability of quarter infection (by major pathogens) from somatic cell concentration.

The herd factor did not significantly affect distributions of somatic cell counts of 6,560 milk samples (collected in 3 herds) within an infection status. Minor-infections distribution for a herd was closer to that of healthy quarters than that of major infections. About 35% of the quarters infected by major pathogens had counts less than 400,000 cells/ml. Statistical analysis by conditional probability indicated that herd major-infection level should be taken into account to predict the probability of quarter infection by major pathogens. Discrimination with a good reliability between presence and absence of pathogens, as estimated by a single somatic cell count, is possible only in herds with high major-infection level.

Age Factors↗

PubMed1982

Approximate confidence intervals for probabilities of survival and quantiles in life-table analysis.

For survival probabilities with censored data, Rothman (1978, Journal of Chronic Diseases 31, 557-560) has recommended the use of quadratic confidence limits based on the assumption that the product of the 'effective' sample size at time t and the life-table estimate of the survival probability past time t follows a binomial distribution. This paper shows that the proposed confidence limits are asymptotically correct for continuous survival data. These intervals, as well as those based on the arcsine transformation, the logit transformation and the log(--log) transformation, are compared by simulation to those based on Greenwood's formula--the usual method of interval estimation in life-table analysis. With large amounts of data, the alternatives to the Greenwood method all produce acceptable intervals. On the basis of overall performance, the intervals suggested by Rothman are preferred for smaller samples. Any of these methods may be used to generate confidence sets for the median survival time or for any other quantile.

Actuarial Analysis↗

PubMed1981

Dependence between the P3-wave and the prestimulus EEG negative shift under conditions of probability prediction.

The connection between the prestimulus slow potential shift (SPS) and the P3-wave of auditory averaged evoked potentials (AEP) from Fz and Cz is studied upon changing the probability and signal characteristics of the stimuli. It has been found that while the changes in the P3-wave, depending on the character of the experimental tasks, are unidirectional for all subjects studied in both recordings and repeat our earlier results, the changes in SPS have different directions. The same changes in P3 are accompanied in some cases by a slightly expressed negativization, in other cases by a certain positivization and in a third group of cases by lack of SPS. The results obtained show that the observed changed in the P3-wave under the conditions of our experiments are not connected with pre-stimulus SPS of the CNV type, being generated in the central nervous system irrespectively of them. They support our hypothesis that the P3-wave is connected with the processes of probability prediction in the brain functioning.

Electroencephalography↗

PubMed1980

Distribution of gene frequencies and discrimination probabilities for 22 human blood genetic systems in four racial groups.

Gene frequencies were computed in four racial categories from 5956 blood donors from California, Hawaii, Mexico City, and Texas. Calculations were based on the phenotypic distribution of 22 blood genetic systems including 7 blood groups and 15 genetically controlled polymorphic proteins and enzymes. Matching probabilities for 20 systems were approximately 1 in 100 000 Asians, 1 in 200 000 blacks, 1 in 330 000 Mexicans, and 1 in 1 000 000 whites. The complementary discrimination probability, which measures the likelihood that two random individuals do not match, was, for practical purposes, unity. The combined new technology for blood grouping and electrophoresis using cellulose acetate membranes provides a powerful individualizing and discriminating tool for forensic science investigation.

Alanine Transaminase↗

PubMed1995

Assessment of individual and population bioequivalence using the probability that bioavailabilities are similar.

In this paper a new method for the assessment of both individual and population bioequivalence is proposed that is derived from the approach of Schall and Luus (1993, Statistics in Medicine 12, 1109-1124). The method considers the probability that the bioavailability of the test product is close to the bioavailability of the reference product, against the probability that the bioavailability of the reference product is close to itself when administered on different occasions. The method can accommodate unequal variances of the bioavailabilities of the test and reference formulations, as well as formulation by subject interaction. It is thus as general and comprehensive as the methods proposed by Sheiner (1992, Statistics in Medicine 11, 1777-1778) and Schall and Luus (1993), but the resulting bioequivalence criteria are simple and easy to interpret.

Acetaminophen↗

PubMed1993

Error-prone polymerization by HIV-1 reverse transcriptase. Contribution of template-primer misalignment, miscoding, and termination probability to mutational hot spots.

We have observed previously that DNA template-directed polymerization by the type 1 human immunodeficiency virus reverse transcriptase is error-prone for single-nucleotide substitution, addition and deletion errors at homopolymeric sequences. We have also noted strong termination of processive synthesis at these positions (Bebenek, K., Abbotts, J., Roberts, J. D., Wilson, S. H., and Kunkel, T. A. (1989) J. Biol. Chem. 264, 16948-16956). Here we have tested three models to explain errors at these hot spots: template-primer misalignment for deletion errors, and dislocation and direct miscoding for substitution errors. The approach involves introducing single-nucleotide changes within or flanking the homopolymeric hot spots and examining the effects that these changes have on human immunodeficiency virus type 1 (HIV-1) reverse transcriptase error rate, error specificity, and termination probability. The results obtained suggest that single-nucleotide deletion errors in homopolymeric runs result from template-primer misalignment and that both direct miscoding and template-primer dislocation contribute to the base substitution hot spots. The data also suggest that base substitution errors at one position can be templated by the preceding nucleotide or either of the next two nucleotides. Frameshift error rates at homopolymeric sites were affected by changes in the sequences flanking the runs, including single-nucleotide differences in the single-stranded template strand and in the double-stranded primer region as many as six nucleotides distant from the hot spot. Both increases and decreases in frameshift fidelity were observed, and most of these correlated with concomitant increases or decreases in the probability that HIV-1 reverse transcriptase terminated processive synthesis within the run. These data provide further support for a relationship between the frameshift fidelity and the processivity of DNA-dependent DNA synthesis by HIV-1 reverse transcriptase.

Base Sequence↗

PubMed1995

[Age, desire for children and probability of pregnancy in The Netherlands].

OBJECTIVE: To investigate the relation between the age of women and their probability of conceiving, and to analyse the factors that influence the age at which couples desire to have their first child. METHOD: A national survey among women between the ages of 25 and 49. A random sample of 8050 households were approached. In these households 3295 women between the ages of 25 and 49 answered a short questionnaire about planning of the first pregnancy and fertility. Also sociodemographic data were gathered. RESULTS: There was little variation in probability of conceiving between the ages of 20 and 28; around 65% to 70% after 6 months, just below 90% after 12 months and about 93% after 2 years. The pregnancy rate after 6 months started to decrease after the age of 33, while pregnancy rate after 1 and 2 years decreased gradually from the age of 28 to 75% and about 80% respectively at the age of 35. The year of birth of the woman (the factor 'time') was the most important factor influencing the age at which couples desire their first child. In addition demographic factors particularly a high level of education, and furthermore a high professional level and a high level of family income were associated with the desire to have the first child at a relatively late age.

Adult↗

PubMed1995

Inferring a major gene for quantitative traits by using segregation analysis with tests on transmission probabilities: how often do we miss?

In an effort to safeguard against false inference of a major gene in segregation analysis, it has become common practice to require nonrejection of the Mendelian-transmission hypothesis (Mendelian tau's) and rejection of the no-transmission hypothesis (equal tau's). However, it is not known how often one would actually infer a major gene, when one exists, by using these criteria. A simulation study was undertaken to investigate this issue. Segregation of a Mendelian gene under a variety of models was simulated in families with both parents and three children. The data were analyzed by using POINTER; the assumptions under the generating and analysis models were identical. By design, the power to reject the no-major-effect hypothesis (q = 0) was > 60% for all models considered; tests on the transmission probabilities were carried out only when q = 0 was rejected, using alpha = 0.05 for all tests. The rates of Mendelian inference were mostly in the range of 22%-50% under recessive inheritance, versus 60%-99% under dominant inheritance. Notably, it was not possible to resolve the transmission (from among Mendelian tau's, equal tau's, and general unconstrained tau's) in approximately 20%-70% of the cases under recessive models, versus 3%-15% under dominant models. Therefore, while tests on transmission probabilities can serve to reduce rates of false inference of a major gene, it is also possible to fail to infer a major gene when one indeed exists, especially under recessive inheritance.

Computer Simulation↗

PubMed1993

Effects of high salt concentration on the open probability of the background chloride channel.

We report here single channel data showing that high concentration of NaCl or CsCl at the cytoplasmic side of the membrane increases the open probability of the background Cl channel from hippocampal neurons. The open probability vs. voltage curve was shifted by 36 mV towards more negative voltages, when salt concentration was raised from 300 to 1000 mM. The steepness of the curve remained unchanged. Possible explanations for this effect are discussed.

Animals↗

PubMed1993

Probability of matching RFLP patterns from unrelated individuals.

RFLP patterns from more than 3,700 individuals, collected by several southeastern laboratories, were compared using a series of mathematical match criteria to determine the probability of randomly matching two samples from different individuals. Data from five loci (D1S7, D2S44, D4S139, D10S28, and D17S79) were compared in all possible combinations. The probability of declaring a false match under any of the match criteria decreased by at least one order of magnitude for each locus added to the comparison. No false matches were declared across four or more loci when match criteria approximately equivalent to that of forensic laboratories were used.

Black People↗

PubMed1993

Mortality Probability Models (MPM II) based on an international cohort of intensive care unit patients.

OBJECTIVE: To revise and update models in the Mortality Probability Model (MPM II) system to estimate the probability of hospital mortality among 19,124 intensive care unit (ICU) patients that can be used for quality assessment within and among ICUs. DESIGN AND SETTING: Models developed and validated on consecutive admissions to adult medical and surgical ICUs in 12 countries. PATIENTS: A total of 12,610 patients for model development, 6514 patients for model validation. Patients younger than 18 years and burn, coronary care, and cardiac surgery patients were excluded. OUTCOME MEASURE: Vital status at hospital discharge. RESULTS: The admission model, MPM0, contains 15 readily obtainable variables. In developmental and validation samples it calibrated well (goodness-of-fit tests: P = .623 and P = .327, respectively, where a high P value represents good fit between observed and expected values) and discriminated well (area under the receiver operating characteristic curve = 0.837 and 0.824, respectively). The 24-hour model, MPM24 (developed on 10,357 patients still in the ICU at 24 hours), contains five of the admission variables and eight additional variables easily ascertained at 24 hours. It also calibrated well (P = .764 and P = .231 in the developmental and validation samples, respectively) and discriminated well (area under the receiver operating characteristic curve = 0.844 and 0.836 in the developmental and validation samples, respectively). CONCLUSIONS: Among severity systems for intensive care patients, the MPM0 is the only model available for use at ICU admission. Both MPM0 and MPM24 are useful research tools and provide important clinical information when used alone or together.

Adult↗

PubMedDate not supplied

[The development of the index of probability of psychosocial adaptation of chronic kidney patients].

Variables obtained from statistical techniques of multivarying analysis, related to psychosocial adaptation of chronic renal patients on treatment were applies in order to construct an index for the probability of the psychosocial adaptation of chronic renal patients (I.P.P.A.C.R.P.). The probability of 1% adaptation determines correctly to 97% of the cases with high sensibility and specificness thus is convenient to wait for the crossed validation of other investigators.

Adaptation, Psychological↗

PubMed1996

The probability of finding a suitable related donor for bone marrow transplantation in extended families.

In bone marrow transplantation, the advantages of family donors over unrelated donors are threefold. (1) Family donors are better matched because they share complete haplotypes. (2) The time between the start of the search and the actual transplantation can be much shorter than for unrelated donors. (3) Related bone marrow transplantation is cheaper. We developed a procedure for calculating the probability of finding a suitable donor among cousins and blood-related aunts and uncles (the extended family). The procedure calculates the following probabilities (P): (1) P that any blood-related uncle or aunt is a suitable donor, (2) P that a suitable donor exists in all blood-related uncles/aunts (from [1]), (3) P that any cousin is a suitable donor (as in [1]), (4) P that a suitable donor exists in all cousins (from [3]), (5) P that a suitable donor exists in the entire extended family (from [2] and [4]). Additionally, we discuss the suitability of this procedure in the daily practice of donor procurement. The procedure is also suitable to search for family donors who have a single antigen mismatch with the patient. We also discuss the differences between our method and the one recently described by Kaufman (Bone Marrow Transplant 15:279, 1995).

Algorithms↗

PubMed1995

[Helpful to bacterial identification: an alternative to probability calculation].

In the field of bacterial identification, the usual probabilistic approach may be criticized to some extent for the way it deals with weak tests. To improve this, we propose a modification which consists to compare the probability of the observed profile to the average of all the possible answers of a given bacteria. The result is discussed and showed to be understood in terms of plausibility rather than probability.

Bacteria↗