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PubMed2005

Comparing Rasch analyses probability estimates to sensitivity, specificity and likelihood ratios when examining the utility of medical diagnostic tests.

INTRODUCTION: Medical diagnostic tests are evaluated based on measures of sensitivity (Sn), specificity (Sp), and likelihood ratios (LR). These procedures are limited in the event of a biased gold standard or missing data. Interpretations of these measures are frequently inappropriate. PURPOSE: The Rasch measurement model (RMM) was examined as a method to provide evidence of diagnostic test utility in order to overcome the limitations of Sn, Sp, and LR. METHODS: Patients suspected of a knee ligament tear (n = 825) were studied, by evaluating four diagnostic tests. The RMM probability estimates for each test were compared to estimates of Sn, Sp, and LR. RESULTS: The RMM provided probability estimates for the diagnosis that were comparable to likelihood ratios. These probability estimates correlated with the estimates of Sn, Sp, and LR. The RMM estimates were not affected by missing data. DISCUSSION: The RMM may provide an alternative means to study the utility of medical diagnostic tests to estimate the probability of disease presence/absence.

Anterior Cruciate Ligament Injuries↗

PubMed2005

Analysis of lymph nodal metastases in malignant melanoma using the poisson probability paradigm and Bayes rule.

This article deals with and formalizes 2 notions common to the practice of pathology. The first is that the number of lymph nodes found positive for metastasis relates directly to the total number of lymph nodes examined. The second is that for any patient, there is a chance that the absence of lymph node metastases is a false-negative result. I introduce the Poisson probability density function to deal with the first notion and the Bayes probability rule to deal with the second. To illustrate the insight these 2 models provide, I apply them to data regarding lymph nodal metastases in malignant melanoma. In this preliminary study, the results of these 2 models correlate well with observed survival probabilities in patients with stage N0 melanoma and with observed rates of false-negative results in sentinel lymph node biopsy technology. With further development, the combination of these models should provide a way to estimate the probability of nodal metastasis when, in fact, none have been observed. Thus, these models might provide useful tools for evaluating patients with stage N0 malignant neoplasms.

Adolescent↗

PubMed1990

Probability of cardiac disease: Framingham revisited.

A study was undertaken to test the utility of a strict Bayesian formulation for the diagnosis of coronary disease. Using known probabilities of the disease for men and women in four different age groups and by estimating the probabilities of disease in patients with four important risk factors, we were able to estimate the probability of coronary disease in 512 different subsets of patients. We found that it was not possible to rigourously apply Bayes formula because neither the probability of the risk factor given the disease nor in patients without disease was obtainable in the medical literature. We conclude that to use Bayes formula without equivocation in coronary diagnosis does not appear possible in the present state of statistical knowledge. Rather, an expert system in the form of a knowledge-base would appear to be more achievable.

Adult↗

PubMed1977

Mathematical model of the summated electromyogram based on the probability characteristics of single motor units.

A probability model for synthesis of the summated electromyogram (EMG) is elaborated on the basis of previous experimental work describing the probability characteristics of the firing of single motor units (MUs) subjected to different external disturbances (e. g. stretch or unloading) and following different instructions for voluntary activation. The possibility is demonstrated some maxima in the summated EMG to be due not to increases excitability of the alpha-motoneurones but to synchronization of the impulses after application of external disturbance, whereby the probability for appearance of impulse in some time intervals will disturbance, whereby the probability for appearance of impulse in some time intervals will increase. The proposed model is used for qualitative studies as a number of factors influencing the value of the signal recorded upon leading off of summated EMG are not taken into account.

Electromyography↗

PubMed1981

[On the position of the human foetus and the probability of spontaneous change in position during pregnancy (author's transl)].

Since ultrasonic examinations became routine practice in pregnancy rather often breech presentations are being found in the course of pregnancy. The amounts of breech, vertex presentation and cross position in the course of pregnancy are shown in a curve which is made from 2.240 single measurements. There are significant differences between primiparae and multiparae as to the frequency of breech and vertex presentation. The analysis of all repeated determinations of fetal presentations allows predications about the probability of changing of a breech into a vertex presentation and vice versa in a determined week of pregnancy. For example the probability of the turning of a breech presentation into a vertex presentation is 44.6% in the 29th week post menstruation, 23.2% in the 33rd week post menstruation. From the 37th week onwards the fetus won't turn any more into the vertex presentation. A vertex presentation, for example in the 29th week post menstruation changes into a breech presentation with a probability of only 0.55%. From the 33rd week onwards a turn into a breech presentation is no longer to be expected. A diagram for the probabilities of the fetal presentations' turnings into the opposite presentations is given for the 13.-40. week post menstruation, from which the patient can immediately be informed about the individual chance. The turn into the vertex presentation is the most common one and seems to be the physiologic one. This turn occurs more or less constantly, not abruptly.

Breech Presentation↗

PubMed1995

Management of probably benign breast lesions.

Several large-scale prospective clinical studies establish the validity of managing probably benign breast lesions with periodic mammographic surveillance as a safe and effective alternative to immediate tissue diagnosis. This approach to mammographic interpretation is now very widely accepted; the American College of Radiology indeed includes "probably benign - short interval follow-up suggested" as one of the five final assessment categories in the Breast Imaging Reporting and Data System (BI-RADS), which all American radiologists are encouraged to use. There is also general consensus that probably benign interpretations should involve (1) cases restricted to nonpalpable lesions; (2) use of the specific imaging criteria described in the prospective clinical studies; and (3) pre-interpretation comparison with prior mammograms, if available, to ensure that new or progressing lesions undergo prompt biopsy (it makes no sense to recommend follow-up for a lesion that has already demonstrated interval progression when the very demonstration of progression during surveillance is what prompts biopsy instead of continued follow-up). As yet unresolved issues concerning probably benign lesions include whether initial full problem-solving imaging should be performed in all cases, whether to use patient age and lesion size (for solitary masses) as additional criteria in deciding between the management alternatives of mammographic follow-up and immediate tissue diagnosis, and what should be the specific timing, frequency, and duration of the follow-up examinations that constitute the surveillance protocol.

Biopsy↗

PubMed1995

Impact of racial genetic polymorphism on the probability of finding an HLA-matched donor.

As successful organ or marrow transplantation correlates with the degree of HLA-compatibility between patient and donor, registries have been developed to facilitate matching. However, racial minority groups have a lower chance of finding a match. We evaluate the impact of the biology of racial genetic polymorphism upon the probability of finding an HLA match for patients of different racial groups. The National Marrow Donor Program has compiled the HLA types of 20,449 patients and 1,625,159 potential volunteer donors. These HLA types were used to estimate the probability of finding an HLA-matched donor for patients of different racial groups. We estimated the HLA haplotype frequencies for different races, and then determined the probability of finding matched donors, given several hypothetical registry sizes. We confirmed that patients of minority races searching the current National Marrow Donor Program registry have low probabilities of finding matches. This was only partly due to the smaller number of donors from these racial minorities, as the observation persisted even when hypothetical donor registry sizes were the same for all racial groups. We demonstrate that African-Americans are more polymorphic with respect to HLA, and are hence less likely to find donors at any given registry size. An increase in the recruitment of minority racial groups for organ and marrow donors will only partially alleviate the problem of equal access to HLA matches for patients belonging to racial minority groups. It will therefore be important to attempt to improve methods for transplantation using HLA-mismatched donors.

HLA Antigens↗

PubMed1994

Publication probability of a study on odds ratio value circumstantial evidence for publication bias in medical study areas.

A summarized odds ratio, calculated from odds ratios of published studies in a meta-analysis, may be overestimated because of publication bias. A method has been developed estimating indirectly the summarized odds ratio of all studies in a given research area, including not only those published but also unpublished. In the present study, a publication probability according to odds ratio value was obtained from the probability density function of all the studies, and a histogram of those published. A publication probability, according to odds ratio value, enables us to infer the quantitative relationship between publication probability and odds ratio. A notable nonpublication of studies whose odds ratios were close to unity was shown from examples of studies on the relationship between passive smoking and lung cancer, whereas nonpublication of studies whose summarized odds ratio was located far from unity was not detected from examples of studies on the relationship between cryptorchidism and testicular cancer. In both study areas, however, the differences between the summarized odds ratios, either with or without the hypothetical unpublished studies, were not large. The small difference, however, should not be ignored, when the study area is recognized as a social problem.

Cryptorchidism↗

PubMed1993

[Probability analysis of the value of ergometry in the detection of restenosis after coronary angioplasty].

To evaluate the usefulness of treadmill exercise test in the diagnosis of coronary restenosis, we have chosen a sequential and probabilistic analysis. The rate of coronary restenosis found in the sample (n = 213) was of 30%. This initial probability of having restenosis was radically changed by the recurrence of typical angina: 77% in patients with this symptom, 17% in those without (p < 0.001). In contrast, the qualitative result of the exercise test was unable to change significantly the probabilities established after anamnesis. This was due to a lower specificity for exercise test (76%) than for angina (93%), the sensibility being the same (56%) for both. Employment of a discriminant value that integrates different ergometric variables did not enhanced sensibility, but allowed the identification of a good number of false positive results and therefore palliated the negative impact of faulty specificity. Being applied to a "discordant group" (no angina/positive exercise test, n = 34) was able to achieve a significant change in probability: from 15% to 50% or 4% (p < 0.01), according to the discriminant being lesser or greater than a preestablished value. In conclusion, prevalence of the event and evaluation of symptomatology are both important to estimate the probability of suffering coronary restenosis. On the contrary, exercise test, in the absence of a weighty method, adds more confusion than clarity to the analysis of the problem. Our results can be used to improve the follow-up of patients who have been successfully dilated by angioplasty.

Angioplasty, Balloon, Coronary↗

PubMed1996

The use of dental radiographs to estimate the probability of cavitation of carious interproximal lesions. Part I: Evidence from the literature.

It is generally recommended that a cavitated, carious lesion be present before an interproximal tooth surface is restored. These lesions often are not clinically visible, however, and must be diagnosed using dental radiographs. Radiographic results can underestimate and overestimate the size of a carious lesion. The purpose of this study was to review and graphically summarize studies that have investigated the relationship between the radiographic image and the presence of a cavitated lesion on the interproximal surfaces of permanent teeth. A search of the literature identified 13 studies, eight of which were suitable for inclusion in our summary. Using the positive and negative likelihood ratios from each study, a graphical summary was developed showing the probability of cavitation based on the radiographic test result and the dentist's pre-radiograph estimate of the probability of cavitation. This graph should allow dentists to more accurately inform their patients of the probability of a cavitated interproximal lesion being present or absent. As a further observation, our findings suggest that to avoid frequent false positive diagnoses, dentists should estimate the probability of cavitation to be at least 30 per cent before they prescribe radiographs for patients who visit them on a regular basis.

Bibliographies as Topic↗

PubMed1997

Estimating the probability of acute appendicitis using clinical criteria of a structured record sheet: the physician against the computer.

OBJECTIVE: To evaluate physicians' probability estimates of acute appendicitis based on structured collection of clinical data. DESIGN: Open prospective study. SETTING: District hospital, Norway. SUBJECTS: 304 patients admitted with suspected acute appendicitis. INTERVENTIONS: Initial diagnostic accuracy of physicians was compared with corresponding results from a computer model. MAIN OUTCOME MEASURES: The estimated probabilities of appendicitis in different testing groups were analysed using receiver operating characteristic (ROC) curves. RESULTS: Physicians' estimates had a mean area under ROC-curve of 0.81 (95% CI 0.79 to 0.82), not significantly different from the computer model. Both correlated well with the actual rate of appendicitis, but the physicians tended to overestimate the probability by 10%. CONCLUSION: Physicians' probability estimates perform rather well. Further attempts to implement a probabilistic approach in the diagnostic process of acute appendicitis therefore seem justified.

Acute Disease↗

PubMed1998

Modulation of neuronal activity in superior colliculus by changes in target probability.

Complex visual scenes require that a target for an impending saccadic eye movement be selected from a larger number of possible targets. We investigated whether changing the probability that a visual stimulus would be selected as the target for a saccade altered activity of monkey superior colliculus (SC) neurons in two experiments. First, we changed the number of possible targets on each trial. Second, we kept the visual display constant and presented a single saccade target repeatedly so that target probability was established over time. Buildup neurons in the SC, those with delay period activity, showed a consistent reduction in activity as the probability of the saccade decreased, independent of the visual stimulus configuration. Other SC neurons, fixation and burst, were largely unaffected by the changes in saccade target probability. Because we had monkeys making saccades to many locations within the visual field, we could examine activity associated with saccades outside of the movement field of neurons. We found the activity of buildup neurons to be similar across the SC, before the target was identified, and reduced when the number of possible targets increased. The results of our experiments are consistent with a role for this activity in establishing a motor set. We found, consistent with this interpretation, that the activity of these neurons was predictive of the latency of a saccadic eye movement and not other saccade parameters such as end point or peak velocity.

Animals↗

PubMed1979

Analysis of probability as an aid in the clinical diagnosis of coronary-artery disease.

The diagnosis of coronary-artery disease has become increasingly complex. Many different results, obtained from tests with substantial imperfections, must be integrated into a diagnostic conclusion about the probability of disease in a given patient. To approach this problem in a practical manner, we reviewed the literature to estimate the pretest likelihood of disease (defined by age, sex and symptoms) and the sensitivity and specificity of four diagnostic tests: stress electrocardiography, cardiokymography, thallium scintigraphy and cardiac fluoroscopy. With this information, test results can be analyzed by use of Bayes' theorem of conditional probability. This approach has several advantages. It pools the diagnostic experience of many physicians ans integrates fundamental pretest clinical descriptors with many varying test results to summarize reproducibly and meaningfully the probability of angiographic coronary-artery disease. This approach also aids, but does not replace, the physician's judgment and may assit in decisions on cost effectiveness of tests.

Adult↗

PubMed1964

FURTHER EXPERIMENTS ON PROBABILITY-MATCHING IN THE PIGEON.

In a discrete-trials, two-key choice situation, probability-learning by pigeons was studied under a variety of training conditions. Matching was found in simultaneous and in successive problems, but a spatial problem produced only maximizing. In the simultaneous problem, noncorrection produced maximizing, while correction produced matching. Guidance produced maximizing when the animals were required to earn each opportunity for choice by pecking a center key on FR-5, but matching when the center key was not used. In a discrete-trials one-key situation, with latency as the measure, frequency and probability of reinforcement were varied independently. Differences in probability produced differences in latency of response, but differences in frequency did not.

Animals↗

PubMed1994

Patients' interpretation of qualitative probability statements.

BACKGROUND: Physicians often use qualitative probability statements to compare treatment options or describe risks of treatment, especially if exact numerical information is not readily available. OBJECTIVES: To determine (1) the effect of context, experience, age, gender, race, occupation, and education on patients' numerical interpretation of probability terms and (2) patient preferences for information about side effects (qualitative or numerical). DESIGN: Cross-sectional survey. SETTING: A university-based family practice in Ann Arbor, Mich. PARTICIPANTS: Patients 18 years of age and older and parents of patients younger than 18 years of age seen during January and February 1993 for any reason except complete physical examination. METHODS: A questionnaire presented scenarios of minor and major complications related to four different medical conditions. Participants were asked to estimate how many people of 100 would have a complication if their physician described the risk for the complication in each scenario as unlikely. Participants were then asked whether they preferred receiving information from their physician about the risk for complications in words or numbers. RESULTS: Of 345 questionnaires distributed, 307 patients (89%) completed them. The rates assigned to the minor complications were significantly higher than the rates assigned to the major complications (P = .0001). Participants who had experienced the described complication reported significantly higher rates for the minor complications of vaccination and surgery (P = .0001 and P = .0235, respectively). Education had a significant effect only on the rates assigned to vaccination complications (P = .0069). Occupation had a significant effect only on the rates assigned to antibiotic side effects (P = .0090). CONCLUSIONS: When a physician uses qualitative probability statements, he or she must be sensitive to the patient's previous experience with that procedure or medication. Also, if one wants to convey the same potential rate of occurrence for major and minor side effects, then one needs to use different words for each.

Adult↗

PubMed1999

Probability of filtration surgery in patients with open-angle glaucoma.

OBJECTIVE: To investigate the probability of undergoing filtration surgery in either 1 or both eyes in patients in whom open-angle glaucoma was newly diagnosed. METHODS AND DESIGN: A retrospective community-based study of 295 residents of Olmsted County, Minnesota, in whom open-angle glaucoma was newly diagnosed between January 1, 1965, and December 31, 1980, was performed. Kaplan-Meier methods were used to estimate the cumulative probability of undergoing filtration surgery during a 20-year period. RESULTS: At 20 years of follow-up, the Kaplan-Meier cumulative probability of undergoing filtration surgery in at least 1 eye was estimated to be 23% (95% confidence interval, 16%-30%), and in both eyes the estimate was 12% (95% confidence interval, 6%-17%). Patients with optic nerve damage at the time of diagnosis were more likely to undergo surgery than patients with elevated intraocular pressure but no damage (1 eye, 39% vs 15%; both eyes, 27% vs 5%). CONCLUSION: This retrospective study of a white population newly diagnosed as having and treated for open-angle glaucoma indicates that while most patients did not undergo filtration surgery in the course of glaucoma therapy, at least one third of those with glaucomatous damage at the time of diagnosis underwent filtration surgery.

Aged↗

PubMed1998

Effect of an intensive educational program for minority college students and recent graduates on the probability of acceptance to medical school.

CONTEXT: Increasing the number of minority physicians is a long-standing goal of professional associations and government. OBJECTIVE: To determine the effectiveness of an intensive summer educational program for minority college students and recent graduates on the probability of acceptance to medical school. DESIGN: Nonconcurrent prospective cohort study based on data from medical school applications, Medical College Admission Tests, and the Association of American Medical Colleges Student and Applicant Information Management System. SETTING: Eight US medical schools or consortia of medical schools. PARTICIPANTS: Underrepresented minority (black, Mexican American, mainland Puerto Rican, and American Indian) applicants to US allopathic medical schools in 1997 (N =3830), 1996 (N = 4654), and 1992 (N =3447). INTERVENTION: The Minority Medical Education Program (MMEP), a 6-week, residential summer educational program focused on training in the sciences and improvement of writing, verbal reasoning, studying, test taking, and presentation skills. MAIN OUTCOME MEASURE: Probability of acceptance to at least 1 medical school. RESULTS: In the 1997 medical school application cohort, 223 (49.3%) of 452 MMEP participants were accepted compared with 1406 (41.6%) of 3378 minority nonparticipants (P= .002). Positive and significant program effects were also found in the 1996 (P=.01) and 1992 (P=.005) cohorts and in multivariate analysis after adjusting for nonprogrammatic factors likely to influence acceptance (P<.001). Program effects were also observed in students who participated in the MMEP early in college as well as those who participated later and among those with relatively high as well as low grades and test scores. CONCLUSIONS: The MMEP enhanced the probability of medical school acceptance among its participants. Intensive summer education is a strategy that may help improve diversity in the physician workforce.

Data Collection↗

PubMed1996

Continuous and group sequential conditional probability ratio tests for phase II clinical trials.

We present continuous and group sequential designs for phase II clinical trials based on the sequential conditional probability ratio test (SCPRT). The SCPRT is derived from a conditional likelihood ratio, where the conditioning is on what the corresponding (reference) fixed sample size test (RFSST) would achieve. In other words, we obtain the sequential design by controlling the maximum probability that the SCPRT does not agree with the RFSST. We shall discuss the difference between SCPRT and stochastic curtailment which also uses the concept of conditional distribution. We show that the power function of the SCPRT is virtually the same as that of the RFSST and its average sample numbers (ASNs) are close to those of Wald's sequential probability ratio test (SPRT), whereas its maximum sample size is no greater than that of the RFSST. Thus the SCPRT has all the desirable properties, such as allowing the use of the RFSST at the last analysis, of the Fleming procedure for phase II trials. The SCPRT, however, preserves the power function of the RFSST better and gives us the option for continuous monitoring. Our recommendation, therefore, is to use a group SCPRT boundary (for interim analyses performed as scheduled) embedded in a continuous SCPRT boundary (for unplanned interim analyses and analyses at times based on data trends). We provide as well a bias-adjusted estimator of the success rate after sequential stopping. We illustrate the method with several examples. The method applies to any single-arm clinical trial with binary endpoints, such as the classic paired design.

Clinical Trials, Phase II as Topic↗