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Biomedical subjects

R S Wigton

Publications and source records attributed to R S Wigton.

At least 19 recordsLinked to original sources
PubMed2005

Selection of predictor variables for pneumonia using neural networks and genetic algorithms.

BACKGROUND: Artificial neural networks (ANN) can be used to select sets of predictor variable that incorporate nonlinear interactions between variables. We used a genetic algorithm, with selection based on maximizing network accuracy and minimizing network input-layer cardinality, to evolve parsimonious sets of variables for predicting community-acquired pneumonia among patients with respiratory complaints. METHODS: ANN were trained on data from 1044 patients in a training cohort, and were applied to 116 patients in a testing cohort. Chromosomes with binary genes representing input-layer variables were operated on by crossover recombination, mutation, and probabilistic selection based on a fitness function incorporating both network accuracy and input-layer cardinality. RESULTS: The genetic algorithm evolved best 10-variable sets that discriminated pneumonia in the training cohort (ROC areas, 0.838 for selection based on average cross entropy (ENT); 0.954 for selection based on ROC area (ROC)), and in the testing cohort (ROC areas, 0.847 for ENT selection; 0.963 for ROC selection), with no significant differences between cohorts. Best variable sets based on the genetic algorithm using ROC selection discriminated pneumonia more accurately than variable sets based on stepwise neural networks (ROC areas, 0.954 versus 0.879, p = 0.030), or stepwise logistic regression (ROC areas, 0.954 versus 0.830, p = 0.000). Variable sets of lower cardinalities were also evolved, which also accurately discriminated pneumonia. CONCLUSION: Variable sets derived using a genetic algorithm for neural networks accurately discriminated pneumonia from other respiratory conditions, and did so with greater accuracy than variables derived using stepwise neural networks or logistic regression in some cases.

Algorithms↗
PubMed2003

Entering the black box of neural networks.

OBJECTIVES: Artificial neural networks have proved to be accurate predictive instruments in several medical domains, but have been criticized for failing to specify the information upon which their predictions are based. We used methods of relevance analysis and sensitivity analysis to determine the most important predictor variables for a validated neural network for community-acquired pneumonia. METHODS: We studied a feed-forward, back-propagation neural network trained to predict pneumonia among patients presenting to an emergency department with fever or respiratory complaints. We used the methods of full retraining, weight elimination, constant substitution, linear substitution, and data permutation to identify a consensus set of important demographic, symptom, sign, and comorbidity predictors that influenced network output for pneumonia. We compared predictors identified by these methods to those identified by a weight propagation analysis based on the matrices of the network, and by logistic regression. RESULTS: Predictors identified by these methods were clinically plausible, and were concordant with those identified by weight analysis, and by logistic regression using the same data. The methods were highly correlated in network error, and led to variable sets with errors below bootstrap 95% confidence intervals for networks with similar numbers of inputs. Scores for variable relevance tended to be higher with methods that precluded network retraining (weight elimination) or that permuted variable values (data permutation), compared with methods that permitted retraining (full retraining) or that approximated its effects (constant and linear substitution). CONCLUSION: Methods of relevance analysis and sensitivity analysis are useful for identifying important predictor variables used by artificial neural networks.

Algorithms↗
PubMed2001

The effect of obesity on medical students' approach to patients with abdominal pain.

Because widely held stereotypes characterize obese people as less intelligent, unhappy, lacking in self control and more prone to psychological problems, we tested whether obese appearance alone would affect medical students' decisions about the diagnosis and management of simulated patients. We videotaped 4 patient simulators presenting each of 4 cases in 2 states: normal and obese (by using padding and bulky clothing). Seventy-two clinical students at 2 medical schools viewed the cases and answered questions about diagnostic tests and management. We found the expected biases toward patients when in their obese form as well as pessimism about patient compliance and success of therapy, but there were no significant differences in tests or treatments ordered except where appropriate for an obese patient (e.g., weight reduction diet). Thus, the appearance of obesity alone biased the students' impressions of the patients, but did not affect diagnostic test ordering.

Abdominal Pain↗
PubMed2001

How physicians diagnose urinary tract infections: the potential influence of laboratory regulations on test availability and use.

OBJECTIVE: Physician office laboratory regulations may decrease test availability. We examined the potential effects of regulations on test availability and whether the use of tests in diagnosing uncomplicated urinary tract infections is related to availability. STUDY DESIGN: We performed an analysis of a cross-sectional survey conducted in 1994 and 1995. Test availability and use were determined by physicians' reports. POPULATION: The survey respondents included practicing physicians in 3 specialties (family medicine, general internal medicine, and obstetrics and gynecology) from 4 states: Pennsylvania (which had longstanding office laboratory regulations), and Alabama, Minnesota, and Nebraska (states that were not regulated until the implementation of the Clinical Laboratory Improvement Amendment of 1988). OUTCOMES MEASURED: We determined whether 4 specific tests were available in the office and how the tests were used to diagnose uncomplicated urinary tract infections. RESULTS: Our analysis was based on the responses from the 1898 respondents to the survey. All tests were less commonly available in Pennsylvania; this included the dipstick, microscopic urinalysis, wet prep, and urine culture (odds ratio [OR]=0.20-0.34; all P values < .05). The availability of the microscopic urinalysis and culture increased their use (OR = 4.37 and 2.03, respectively; P=.001). The availability of microscopic urinalysis was associated with a decrease in ordering urine cultures (OR=0.42; P=.001), and the availability of the dipstick was associated with a decrease in the use of both the microscopic urinalysis (OR=0.36; P=.02) and the culture (OR=0.48; P=.05). CONCLUSIONS: We found lower test availability in the state with office laboratory regulations and a decrease in testing when availability is reduced, suggesting that laboratory regulations may influence physicians&rsquo diagnostic approach to urinary tract infections. Further study will be required to determine the level of testing that maximizes patient welfare.

Adult↗
PubMed2000

Procedural experience and comfort level in internal medicine trainees.

BACKGROUND: The American Board of Internal Medicine (ABIM) has recommended a specific number of procedures be done as a minimum standard for ensuring competence in various medical procedures. These minimum standards were determined by consensus of an expert panel and may not reflect actual procedural comfort or competence. OBJECTIVE: To estimate the minimum number of selected procedures at which a majority of internal medicine trainees become comfortable performing that procedure. DESIGN: Cross-sectional, self-administered survey. SETTING: A military-based, a community-based, and 2 university-based programs. PARTICIPANTS: Two hundred thirty-two internal medicine residents. MEASUREMENTS: Survey questions included number of specific procedures performed, comfort level with performing specific procedures, and whether respondents desired further training in specific procedures. The comfort threshold for a given procedure was defined as the number of procedures at which two thirds or more of the respondents reported being comfortable or very comfortable performing that procedure. RESULTS: For three of seven procedures selected, residents were comfortable performing the procedure at or below the number recommended by the ABIM as a minimum requirement. However, residents needed more procedures than recommended by the ABIM to feel comfortable with central venous line placement, knee joint aspiration, lumbar puncture, and thoracentesis. Using multivariate logistic regression analysis, variables independently associated with greater comfort performing selected procedures included increased number performed, more years of training, male gender, career goals, and for skin biopsy, training in the community-based program. Except for skin biopsy, comfort level was independent of training site. A significant number of advanced-year house officers in some programs had little experience in performing selected common ambulatory procedures. CONCLUSION: Minimum standards for certifying internal medicine residents may need to be reexamined in light of house officer comfort level performing selected procedures.

Adult↗
PubMed1999

Variation by specialty in the treatment of urinary tract infection in women.

To determine practicing physicians' strategies for diagnosing and managing uncomplicated urinary tract infection, we surveyed physicians in general internal medicine, family practice, obstetrics and gynecology, and emergency medicine in four states. Responses differed significantly by respondents' specialty. For example, nitrofurantoin was the antibiotic of first choice for 46% of obstetricians, while over 80% in the other specialties chose trimethoprim-sulfamethoxazole. Most surveyed said they do not usually order urine culture, but the percentage who do varied by specialty. Most use a colony count of 10(5) colony-forming units or more for diagnosis although evidence favors a lower threshold, and 70% continue antibiotic therapy even if the culture result is negative. This survey found considerable variation by specialty and also among individual physicians regarding diagnosis and treatment of urinary tract infection and also suggests that some of the new information from the literature has not been translated to clinical practice.

Adult↗
PubMed1997

Factors explaining variability among caregivers in the intent to restrict life-support interventions in a pediatric intensive care unit.

OBJECTIVE: To explore patient-related factors which influence the decisions of pediatric intensive care unit (ICU) caregivers to restrict life-support interventions. DESIGN: Cross-sectional survey. SETTING: A university-affiliated pediatric ICU. SUBJECTS: All physicians and nurses caring for oncology or cardiology ICU patients. INTERVENTIONS: Seven patient characteristics were systematically presented in 16 theoretical case scenarios. MEASUREMENTS AND MAIN RESULTS: Individual linear regression models were constructed for each participant by calculating the importance caregivers placed on seven patient characteristics when deciding about starting intravenous vasopressors, performing chest compressions, and withdrawing life support. We compared the numerical and descriptive (very low, low, moderate, high) probability of survival. We surveyed 86 caregivers and 56 (65%) responded. The most important factors influencing decisions were family preferences (76% of decisions), followed by probability of survival (50%), and functional status (47%). There was marked variability among respondents in 38 (79%)/48 of the questions; 20% to 50% of caregivers chose opposing directions of patient management when they were asked to indicate the likelihood that they would perform a specific life-support intervention. The same term was never used by all respondents to describe the probability of survival for a scenario. CONCLUSION: Critically ill children and their families could face markedly different attitudes about the restriction of life-support interventions, depending on which nurses and physicians are involved in their care.

Activities of Daily Living↗
PubMed1996

Attitudes and expectations of 1995 gastroenterology graduates about gastroenterology.

OBJECTIVE: To learn more about current attitudes and expectations of recent (June 1995) graduates of gastroenterology fellowship programs, why they chose either a private practice or academic career, and what impact managed care or health care reform had in their decision. METHODS: Between April and June 1995, and 8-page, 35-question survey questionnaire was mailed to graduating fellows and returned for evaluation. RESULTS: Graduates believed managed care had an impact on job availability, but it was not a factor in their job choice. Forty percent of the respondents reported that finding a job was either difficult or very difficult. The majority of respondents (67%) are pursuing a career in private practice. Most private practice physicians (PP) trained in 2-yr programs whereas academic physicians (AC) trained for the most part in 3-yr programs. The principal criteria on which decisions regarding job selection were based were similar between the two groups: co-workers, geographic location, access to patient care, and ability to perform endoscopy. Respondents in PP and AC expected to work 50-70 h/wk, care for patients with similar diseases, and have ample time for family. They would choose GI again as a career and believed that there is a future in GI. Salary expectations varied markedly between the two groups, and AC physicians were more concerned about their future financial needs. Twenty percent of PP physicians and 71% of AC physicians plan to participate in clinical research. CONCLUSIONS: Recent graduates of gastroenterology fellowship programs continue to have high expectations of their future careers. Although some had difficulty finding a job and stated that, although managed care had an impact on the job market, it had not yet become a major factor in their job selection.

Adult↗
PubMed1995

Procedural skills of practicing pulmonologists. A national survey of 1,000 members of the American College of Physicians.

We surveyed pulmonologists to determine which procedures they do in practice, where they learned the procedures, and how much training they recommend to attain and maintain clinical competence in each. We mailed a survey to a random sample of 1,000 members of the American College of Physicians who were identified as practicing pulmonologists; 755 (75%) responded. Respondents performed a variety of pulmonary procedures, an average of 17 of the 29 listed. Pulmonologists who were more recent graduates, who worked longer hours, and who were involved in critical care did a greater variety of procedures. Only 26% of practicing pulmonologists currently do all the procedures required for board certification in pulmonary medicine. For each of 13 specific procedures, the number reported done in the past year was generally unrelated to practice factors. Many respondents who learned procedures in practice did so without formal training or supervision. Respondents' recommendations regarding numbers of procedures required to attain or maintain competence did not vary greatly. Pulmonologists vary considerably in the types of procedures they do. Their opinions about the training needed for competence help to better define requirements for training programs. More attention should be focused on training and certifying practicing pulmonologists in procedures learned after formal fellowship training.

Adult↗
PubMed1993

Discrimination and reproducibility of an information maximizing multivariable model.

Predictor variables for multivariate rules are frequently selected by methods that maximize likelihood rather than information. We compared the discrimination and reproducibility of a prediction rule for pneumonia derived using extended dependency analysis (EDA), an information maximizing variable selection program, with that of a validated rule derived using logistic regression. Discrimination was measured by receiver-operating characteristic (ROC) analysis, and reproducibility by rederivation of the rule on 200 replicate samples of size 250 and 500, generated from a training cohort of 905 patients using Monte Carlo techniques. Four of the five predictor variables selected by EDA were identical to those selected by logistic regression. With each variable weighted by its conditional contribution to total information transmission, EDA discriminated pneumonia and nonpneumonia in the training cohort with an ROC area of 0.800 (vs 0.816 for logistic regression, p = 0.60), and in the validation cohort with an area of 0.822 (vs 0.821 for logistic regression, p = 0.98). EDA demonstrated reproducibility comparable to that of logistic regression according to most criteria for replicability. Replicate EDA models showed good discrimination in the training and testing cohorts, and met statistical criteria for validation (no significant difference in ROC areas at a one-tailed alpha level of 0.05) in 80.8% to 94.2% of cases. We conclude that extended dependency analysis selected the most important variables for predicting pneumonia, based on a validated logistic regression model. The information-theoretic model showed good discriminatory power, and demonstrated reproducibility according to clinically reasonable criteria. Information-theoretic variable selection by extended dependency analysis appears to be a reasonable basis for developing clinical prediction rules.

Cohort Studies↗
PubMed1992

Training internists in procedural skills.

The procedural skills of internists have been scrutinized recently because of concern for quality of care and because of economic and liability issues. The findings of recent surveys of program directors and practicing internists about procedural skills are reviewed. The results of these surveys in relation to the American Board of Internal Medicine's (ABIM) new training requirements and New York State's new policy requiring credentialing of residents in training are also discussed. Surveys show that internists do a large number and variety of procedures, that the number of procedures varies with the nature and location of practice, and that internists who more recently completed training do more procedures. Many graduates do not master the procedures their program directors think they should, and many learn procedures, often without supervision, after they have entered practice. The ABIM has recently ruled that residents must have documented experience and competence in specific core procedures to become eligible for certification. Also, New York State, in the wake of the Libby Zion case, now requires that all residents be credentialed in the procedures they do during training. Programs in internal medicine need to decide which procedures their residents will master and assure that their residents receive the training and testing necessary for competency and for formal certification of mastery in each procedure. Programs may restructure rotations to assure adequate experience. In the new era of accountability, certification of training and of competence in procedural skills will be an important function of training programs.

Certification↗
PubMed1992

Controlled trial using computerized feedback to improve physicians' diagnostic judgments.

The goal of this study was to test an innovative method to improve physicians' diagnostic judgments by integrating the use of a computer program (employing cognitive feedback to teach a clinical rule that predicts the probability of streptococcal pharyngitis), a traditional lecture, and periodic disease-prevalence reports. In a controlled trial using pre- and postintervention measures involving 885 patients, the authors compared the effects of the integrated method on the diagnostic judgments of seven experienced physicians at a university health service (from 1982 to 1985) with the effects of the lecture alone on the judgments of seven experienced physicians at a different university health service (1986 to 1987). The integrated method significantly improved the quality of the physicians' judgments as measured by calibration curves and Brier scores, and increased the level of agreement between the physicians' judgments and those made by the clinical prediction rule. The lecture alone produced less improvement in the quality of the physicians' judgments, and decreased the level of agreement with the rule. The authors conclude that this method, based on cognitive psychology, is a promising educational tool.

Computer-Assisted Instruction↗