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PubMed1997

Probable locally acquired mosquito-transmitted Plasmodium vivax infection--Georgia, 1996.

Endemic, mosquitoborne transmission of malaria was interrupted in the United States during the 1940s. Since then, 57 small localized outbreaks of probable mosquito-transmitted malaria in the United States have been reported to CDC. This report summarizes the investigation of a case of Plasmodium vivax infection in a resident of Georgia who had never lived in or visited a malarious area. The results of this investigation suggest that this case probably was acquired through the bite of a locally infected Anopheles sp. mosquito, although a probable source of infection for mosquitoes was not confirmed.

Animals↗

PubMed1997

Human visual sensitivity to plumes with a Gaussian luminance distribution: experiments to develop an empirical probability of detection model.

This paper discusses results of a research project designed to develop an empirical model that could be used as a tool to predict human visual sensitivity to plumes. The resultant probability of detection algorithm (PROBDET) allows one to estimate the probability of a plume of known size, shape and contrast being detected visually. As a basis for the algorithm, a series of laboratory experiments using a high threshold signal detection procedure and computer generated images of plumes with Gaussian luminance distributions was conducted to measure human visual sensitivity to plumes. Results of the laboratory experiments are compared with results of contrast sensitivity experiments that examined visual sensitivity to stimuli with square and sine wave luminance distributions. An example of the PROBDET algorithm is presented to demonstrate its potential usefulness for assessing how probability of detection estimates change as plume size and contrast parameters vary. Since this research was designed to build on existing knowledge, a discussion of that knowledge and how it relates to the research conducted is also presented. The focus of this discussion is on the human visual system (HVS) and on how visual sensitivity is affected by factors such as the luminance of the stimulus and the surround, the luminance distribution of the stimulus, the size of the surround, and the size and spatial frequency characteristics of the stimulus.

Adult↗

PubMed1997

The role of a decision rule in symptomatic pulmonary embolism patients with a non-high probability ventilation-perfusion scan.

BACKGROUND: In order to improve the use of information contained in the medical history and physical examination in patients with suspected pulmonary embolism and a non-high probability ventilation-perfusion scan, we assessed whether a simple, quantitative decision rule could be derived for the diagnosis or exclusion of pulmonary embolism. METHODS: In 140 consecutive symptomatic patients with a non-high probability ventilation-perfusion scan and an interpretable pulmonary angiogram, various clinical and lung scan items were collected prospectively and analyzed by multivariate stepwise logistic regression analysis to identify the most informative combination of items. RESULTS: The prevalence of proven pulmonary embolism in the patient population was 27.1%. A decision rule containing the presence of wheezing, previous deep venous thrombosis, recently developed or worsened cough, body temperature above 37 degrees C and multiple defects on the perfusion scan was constructed. For the rule the area under the Receiver Operating Characteristic curve was larger than that of the prior probability of pulmonary embolism as assessed by the physician at presentation (0.76 versus 0.59; p = 0.0097). At the cut-off point with the maximal positive predictive value 2% of the patients scored positive, at the cut-off point with the maximal negative predictive value pulmonary embolism could be excluded in 16% of the patients. CONCLUSIONS: We derived a simple decision rule containing 5 easily interpretable variables for the patient population specified. The optimal use of the rule appears to be in the exclusion of pulmonary embolism. Prospective validation of this rule is indicated to confirm its clinical utility.

Adult↗

PubMed1997

Probability of valid gait data acquisition using currently available force plates.

A major difficulty in using force plates for gait analysis is to have a foot fall completely on the instrument while not having the other foot in contact with the same device. This translates into more trials (and time) required to obtain valid data. In order to estimate the probability of a successful trial, which is related to the overall number of trials required, the dimensional relationships between force plate, foot and gait cycle were investigated. In particular, it was analyzed how the dimensions of the plate, the size of foot, the step length and width affect the probability of having a successful trial when acquiring one or two subsequent foot falls using one or two force plates respectively. The equations obtained can also be used to estimate the force plate dimensions that allow for the minimum number of trials for a specific group of subjects. To illustrate this approach, commercially available force plate sizes were statistically evaluated using gait data collected in recent years at The Ohio State University Gait Laboratory from patients with different pathologies. The force plate length maximizing the probability of a successful trial was identified for this specific population.

Adolescent↗

PubMed1998

Nonpalpable, probably benign breast lesions in general practice: the role of follow-up mammography.

A nonpalpable, probably benign lesion is frequently detected on mammograms. The aim of this paper was to determine the role of follow-up mammography as an alternative to surgical biopsy of these lesions, in patients from a general practice population. In a prospective study we estimated the compliance rate of general practitioners and patients with the recommendations for mammographic follow-up of nonpalpable, probably benign lesions. Reasons for noncompliance, the value of a reminder and the probability of malignancy were determined.

Breast Diseases↗

PubMed1998

Percent free prostate-specific antigen in assessing the probability of prostate cancer under optimal analytical conditions.

Although general consensus exists that percent free prostate-specific antigen (PSA) is superior to total immunoreactive PSA for prostate cancer (CaP) detection, its diagnostic performance is not yet well established. Analytical problems may account for difficulties in evaluating percent free PSA because the free PSA concentration is substantially lower than that of total PSA. The aim of the present study was to establish the diagnostic performances of the IMMULITE percent free PSA assay from Diagnostics Products Corp. under experimental conditions optimized to minimize analytical variability. Eighty-five patients with untreated primary CaP and 261 with untreated benign prostate hypertrophy (BPH) were prospectively enrolled. The Diagnostics Products IMMULITE total (Third Generation) and free PSA were measured by the same technician, using the same instrument and the same reagent batch. We calculated the post-test probability to express how the likelihood of the diagnosis of CaP changed after the percent free PSA was determined. Areas under the ROC curves of percent free PSA were better than those of total PSA in every evaluated range of total PSA. The percent free PSA could have reduced the rate of unnecessary biopsies by 47% in patients with total PSA >/=4 microg/L with only 3.8% false-negative results. The post-test probability of percent free PSA was, however, <50% in men 50-70 years of age, using cutoff points providing sensitivity from 99% to 80%. Percent free PSA is superior to total PSA in distinguishing primary CaP from BPH in patients with total PSA between 2 and 30 microg/L. In men with low total PSA, the diagnostic performance of the percent free PSA assay may be optimized by controlling methodological variability. The percent free PSA assay is effective in reducing the rate of unnecessary biopsies in men with total PSA >4 microg/L. However, the post-test probability provided by percent free PSA is relatively low in asymptomatic patients 50-70 years of age.

Aged↗

PubMed1986

Probability theory in the use of diagnostic tests. An introduction to critical study of the literature.

The purpose of this article is to provide an understanding of methods that are useful in formulating advice about when to use diagnostic tests. If the clinician expresses diagnostic uncertainty as the probability of a disease in a patient, Bayes' theorem may be used to predict the effect of doing various tests and their impact on patient management. To use Bayes' theorem wisely, one must be aware of pitfalls in estimating probability and must understand the limitations of most studies of the sensitivity and specificity of diagnostic tests.

Bayes Theorem↗

PubMed2002

Untreated gonococcal and chlamydial infection in a probability sample of adults.

CONTEXT: The prevalence and distribution of gonococcal and chlamydial infections in the general population are poorly understood. Development of nucleic acid amplification tests, such as the ligase chain reaction assay, provides new opportunities to estimate the prevalence of untreated infections in the population. OBJECTIVE: To estimate the overall prevalence of untreated gonococcal and chlamydial infections and to describe patterns of infection within specific demographic subgroups of the young adult population in Baltimore, Md. DESIGN AND SETTING: Cross-sectional behavioral survey based on a probability sample of Baltimore households with collection of urine specimens between January 1997 and September 1998. PARTICIPANTS: A total of 728 adults aged 18 to 35 years completed the interview portion of the study, and 579 of these respondents also provided a urine specimen adequate for testing. MAIN OUTCOME MEASURE: Prevalence of untreated infection, as measured by the percentage of specimens testing positive for gonococcal and chlamydial infection by ligase chain reaction, weighted to reflect variations in probabilities of sample selection from the population. Alternate estimates of the prevalence of recent treated infection were derived from clinically diagnosed cases reported to the Baltimore City Health Department and by diagnoses reported by participants in the survey. RESULTS: An estimated 5.3% (SE, 1.4%) of the population aged 18 to 35 years has an untreated gonococcal infection, and 3.0% (SE, 0.8%) is estimated to have an untreated chlamydial infection. While 7.9% (SE, 1.6%) of the population is estimated to have either an untreated gonococcal or chlamydial infection, estimated prevalence is substantially higher among black women (15.0%; SE, 3.7%). Few participants with untreated infections reported dysuria or discharge during the 6 months preceding testing. The estimated number of untreated gonococcal infections in the population (9241; SE, 2441) substantially exceeds both the number of such infections diagnosed among Baltimore adults aged 18 to 35 years and reported to the Baltimore City Health Department during 1998 (4566), and the estimated number of diagnoses derived using participants' reports for the 12 months prior to the survey (4708 [SE, 1918] to 5231 [SE, 2092]). The estimated number of untreated chlamydial infections (5231; SE, 1395) is also greater than the number of cases reported to the health department in 1998 (3664) but is slightly less than the estimated number of diagnoses derived using participants' reports of chlamydial infections diagnosed during the 12 months prior to the survey (5580 [SE, 1918] to 6975 [SE, 2441]). CONCLUSION: In 1997-1998, the estimated number of undiagnosed gonococcal and chlamydial infections prevalent in the population of Baltimore adults aged 18 to 35 years approached or exceeded the number of infections that were diagnosed and treated annually.

Adult↗

PubMed1999

Estimation of failure probabilities in the presence of competing risks: new representations of old estimators.

A topic that has received attention in both the statistical and medical literature is the estimation of the probability of failure for endpoints that are subject to competing risks. Despite this, it is not uncommon to see the complement of the Kaplan-Meier estimate used in this setting and interpreted as the probability of failure. If one desires an estimate that can be interpreted in this way, however, the cumulative incidence estimate is the appropriate tool to use in such situations. We believe the more commonly seen representations of the Kaplan-Meier estimate and the cumulative incidence estimate do not lend themselves to easy explanation and understanding of this interpretation. We present, therefore, a representation of each estimate in a manner not ordinarily seen, each representation utilizing the concept of censored observations being 'redistributed to the right.' We feel these allow a more intuitive understanding of each estimate and therefore an appreciation of why the Kaplan-Meier method is inappropriate for estimation purposes in the presence of competing risks, while the cumulative incidence estimate is appropriate.

Confounding Factors, Epidemiologic↗

PubMed1999

Probability-based protein identification by searching sequence databases using mass spectrometry data.

Several algorithms have been described in the literature for protein identification by searching a sequence database using mass spectrometry data. In some approaches, the experimental data are peptide molecular weights from the digestion of a protein by an enzyme. Other approaches use tandem mass spectrometry (MS/MS) data from one or more peptides. Still others combine mass data with amino acid sequence data. We present results from a new computer program, Mascot, which integrates all three types of search. The scoring algorithm is probability based, which has a number of advantages: (i) A simple rule can be used to judge whether a result is significant or not. This is particularly useful in guarding against false positives. (ii) Scores can be compared with those from other types of search, such as sequence homology. (iii) Search parameters can be readily optimised by iteration. The strengths and limitations of probability-based scoring are discussed, particularly in the context of high throughput, fully automated protein identification.

Amino Acid Sequence↗

PubMed1987

Making the most of multiple measurements in estimating carrier probability in Duchenne muscular dystrophy: the Bayesian incorporation of repeated measurements using logistic discrimination.

In carrier detection studies, females-at-risk are usually tested several times if the results are ambiguous, whereas subjects in the control and obligate carrier reference groups may not be tested as often. The question is how to incorporate the multiple measurements most effectively with information in the family pedigree into combined carrier risks. Sets of measurements on individuals are not independent, but are related with the correlation coefficient 0 less than rho less than 1. We have developed a procedure for incorporating repeated measurements on individuals and their a priori chance of having the disease into logistic models. This procedure utilizes the set of measurements and an estimate of rho. We describe application of this procedure to carrier detection in Duchenne muscular dystrophy (DMD) using serum creatine kinase (CK) measurements as the biochemical indicator of carrier status. Estimates of rho for controls and obligate DMD carriers did not differ significantly from 0.5. Repeated testing with use of rho = 0.5 significantly decreased the median logistic carrier probability for controls and increased it for carriers. In some cases four to six rather than the three CK tests conventionally used in genetic counseling were necessary to obtain a stable logistic carrier probability for a subject.

Creatine Kinase↗

PubMed1987

Psychological aspects of genetic counseling. IV. The subjective assessment of probability.

Subjects asked to compare mathematically equal statements (or frames) of probability invariably perceived a difference in magnitude between percentages and equivalent proportions. Presented as unrelated to genetic risk, percentages tended to be chosen as having greater magnitude than their equivalent proportions. In justifying their choices subjects used a process of reasoning in which numbers were mentally compared, contrasted, or otherwise manipulated (numerical strategy). When framed as genetic risks, two types of reasoning were used to assess probabilities, the numerical strategy and one involving mental images of persons or parts of persons (person strategy). Subjects who used numerical reasoning tended to perceive percentages as having a greater risk magnitude than equivalent proportions whereas when person reasoning was used proportions with denominators of 10 or less tended to be perceived as having a greater risk magnitude than equivalent percentages. The implications of the findings for genetic counseling are discussed.

Adult↗

PubMed1984

A genetic model of dental reduction through the probable mutation effect.

A simulation approach is used in order to elucidate the nature of the hypothesized "probable mutation effect" as it applies to dental reduction in man. Computer-generated simulations of the accumulation of mutations in a human gene pool show the results of the proposed model under the influence of various parameters, as well as illustrating the nature of such genetic change through time. This approach supports a polygenic model of the probable mutation effect as a viable hypothesis for an explanation of the dental reduction which has occurred in some human populations over the last 40,000 years.

Humans↗

PubMed1994

Patients' interpretations of verbal expressions of probability: implications for securing informed consent to medical interventions.

Physicians often use verbal expressions of probability to characterize their uncertainty about outcomes and the risks or side effects of proposed therapies. However, there is an extensive literature that documents the inherent vagueness of such expressions. Because of the potential importance of probability terms to physician-patient communication and decision-making, we asked patients to tell us the odds they thought applicable to the term "rare," as used by their physician to discuss the likelihood of an adverse outcome from surgery. Patients were randomly assigned to one of three outcome groups: death, severe heart attack, or severe pneumonia. Demographic data were elicited from each subject, as were indicators of present health status, medical history for certain diseases and surgery, and life expectancy. Linear regression and ANOVA analyses of the responses indicate that patient age, education level, perceived health status, and recency of experience with disease and medical care influence patients' numeric interpretations. We discuss the implications of these results.

Adult↗

PubMed2006

Development and validation of nomograms for predicting residual tumor size and the probability of successful conservative surgery with neoadjuvant chemotherapy for breast cancer.

BACKGROUND: Neoadjuvant chemotherapy (NACT) increases the likelihood that breast conservation therapy for breast cancer patients will be successful. There is no available nomogram to predict breast conservation after NACT. The aim of the current study was to develop and validate nomograms for predicting residual tumor size and probability of a patient becoming eligible for breast conservation surgery after NACT. METHODS: A total of 1147 patients treated at M. D. Anderson Cancer Center (Houston, TX) and the Institut Gustave Roussy (Villejuif, France) who received anthracycline with or without paclitaxel NACT were included in the analysis. Clinicopathologic data from 1 series were used to construct logistic regression models for breast conservation and residual tumor size < 3 cm after NACT and were validated on an independent series. RESULTS: The discrimination and the calibration of the nomogram for predicting the probability of residual tumor size < 3 cm after anthracycline-based NACT were good when applied to the validation set (concordance index = 0.79; U-index = 10(-3)). The discrimination of the nomogram for predicting eligibility for breast conservation therapy was also good (concordance index = 0.67). However, the calibration had to be adjusted to take into account global rates of breast conservation surgery. A second nomogram adapted to preoperative chemotherapy regimens containing paclitaxel was established. The concordance index of the nomogram for predicting breast conservation was 0.71 (P < 10(-6)) for the independent dataset and the calibration was also good. The confrontation of both nomograms showed that predictions were highly correlated (r = 0.97), suggesting that eligibility for breast conservation therapy was independent of the preoperative chemotherapy regimen used. CONCLUSIONS: Nomograms were developed for breast cancer patients who received NACT to predict residual tumor size and whether the patient would thus become eligible for breast conservation therapy. These tools may be useful when counseling patients about treatment options, and a web-based interface is now available to help guide patients and physicians in these decisions.

Anthracyclines↗

PubMed1995

Theory of the mobility-shift assay of nonspecific protein-DNA complexes governed by conditional probabilities: the HU:DNA complex.

Complexes of an 88 bp DNA and the HU protein were studied by both experimental and theoretical electrophoretic mobility-shift analyses. Experimental analysis defined the stoichiometry of binding and estimated an apparent intrinsic dissociation constant (Kd = 1 to 3 x 10(-7) M) for the HU:DNA complexes. The theory of conditional probabilities was applied to the binding of HU to DNA in order to fix the initial equilibrium composition of mixtures to be assayed theoretically by the mobility-shift procedure. Electrophoretic mobility-shift patterns were obtained by numerical solution of a set of simultaneous transport-reaction equations, in which the chemical kinetic term is formulated in terms of dissociation of the different DNA:HU complexes in gel cages. The computed patterns simulated the experimental patterns describing the titration of a fixed concentration of an 88 bp DNA fragment with dimeric HU. These insightful results provide guidelines for interpretation of the electrophoretic behavior of systems in which a ligand binds nonspecifically to DNA. In particular, the narrow unresolved zone observed both experimentally and theoretically beyond 50-60% saturation is a reaction zone characteristic of noncooperative ligand-binding governed by conditional probabilities. The discrepancy between the theoretically assigned and experimental values of the intrinsic binding constant is attributed to an HU-induced change in the conformation of DNA.

Bacterial Proteins↗

PubMed1988

Myogenic stem cell commitment probability remains constant as a function of organismal and mitotic age.

Chicken myogenic stem cells can undergo symmetric and asymmetric cell divisions. Symmetric divisions produce two stem cells or two cells committed to terminal muscle differentiation. Asymmetric divisions produce one stem cell and one committed cell. Committed cells undergo four divisions, and their progeny differentiate into postmitotic, biochemically distinct muscle cells, which can be identified immunocytochemically. The control of stem cell commitment was investigated in vitro by means of cell cloning and subcloning experiments, and computer modeling. We found that stem cell commitment is a process which can be modeled as a stochastic event, with a central tendency or probability of 0.2 +/- 0.1. This value is independent of organismal or mitotic age of the stem cells, cell density, or growth in a mitogen-poor environment. Myogenic stem cells stop dividing after approximately 30 divisions in vitro. Since the probability of commitment to terminal differentiation remains below 0.5, clonal senescence and terminal differentiation are separate processes in this system.

Animals↗

PubMed1996

MR image segmentation using vector decomposition and probability techniques: a general model and its application to dual-echo images.

A general model is developed for segmenting magnetic resonance images using vector decomposition and probability techniques. Each voxel is assigned fractional volumes of q tissues from p differently weighted images (q < or = p + 1) in the presence of partial-volume mixing, random noise, and other tissues. Compared with the eigenimage method, fewer differently weighted images are needed for segmenting the q tissues, and the contrast-to-noise ratio in the calculated fractional volumes is improved. The model can produce composite tissue-type images similar to that of the probability methods, by comparing the fractional volumes assigned to different tissues on each voxel. A three-tissue (p = 2, q = 3) model is illustrated for segmenting three tissues from dual-echo images. It provides statistical analysis to the algebraic method. A three-compartment phantom is segmented for validation. Two clinical examples are presented.

Artifacts↗