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Biomedical subjects

C B Begg

Publications and source records attributed to C B Begg.

101 records · Page 6Linked to original sources
PubMed1976

Use of coagulation tests to predict the clinical progress of pre-eclampsia.

The clinical manifestations of severe pre-eclampsia are normally separated from those of mild pre-eclampsia and normal pregnancy on arbitrary grounds. A clinical index, based on the increase in diastolic blood-pressure and the presence of proteinuria, was developed to reflect the spectrum of disease from mild to severe pre-eclampsia. This was related to a coagulation index based on the platelet-count, plasma-factor-VIII, and serum-fibrinolytic-degradation-products. The two indices were shown to be strongly correlated. All cases of perinatal death associated with pre-eclampsia had coagulation indices in the most severely abnormal range. These results suggest that intravascular coagulation is a highly characteristic feature of pre-eclampsia and that the coagulation index may be of value in monitoring the progress of the disease.

Blood Cell Count↗
PubMedDate not supplied

A measure to aid in the interpretation of published clinical trials.

The published literature contains numerous reports of clinical studies. A problem in their interpretation is that studies in which the observed efficacy of the treatment is high are much more likely to be reported than those in which the observed efficacy is average or poor. This phenomenon has had the consequence of generally discrediting the reliability of the literature, especially that of non-randomized studies. In this paper a model is developed which permits estimation of the potential magnitude by which the reported efficacy of a treatment might be inflated. This quantity is termed the publication bias. The magnitude of the bias depends on the sample size of the study and the number of similar studies conducted concurrently. Tabulated values of the bias are presented, permitting easy computation. The new measure may have potential use for physicians in clinical decision making in that it characterizes the reliability of results from a specific published study, especially when there are no definitive randomized studies. However, correction of publication bias in this manner is not a substitute for a well controlled or a randomized study. The technique merely assists in the interpretation of available evidence from the literature. Moreover, it must be used with due caution in recognition of the assumptions and approximations involved in the calculation.

Attitude↗
PubMedDate not supplied

Treatment allocation methods in clinical trials: a review.

A comprehensive review of methods for allocation of treatments to patients in clinical trials is presented. Attention is restricted to controlled, prospective trials, as opposed to comparisons involving historical or other 'external' controls. We describe the features of each method and classify them according to whether their primary focus is randomization, efficiency, or balance with respect to prognostic factors. Methods which prevent bias, ensure an efficient treatment comparison and are simple to implement will contribute to the ability of clinical trials to provide precise and valid treatment comparisons. We assess critically the extent to which the methods achieve these goals, review the relationships of the allocation methods with subsequent analyses of the trial results, discuss current usage and provide guidelines for choice of method.

Biometry↗
PubMedDate not supplied

A general regression methodology for ROC curve estimation.

A method for applying generalized ordinal regression models to categorical rating data to estimate and analyze receiver operating characteristic (ROC) curves is presented. These models permit parsimonious adjustment of ROC curve parameters for relevant covariates through two regression equations that correspond to location and scale. Particular shapes of ROC curves are interpreted in relation to the kind of covariates included in the two regressions. The model is shown to be flexible because it is not restricted to the assumption of binormality that is commonly employed in smoothed ROC curve estimation, although the binormal model is one particular form of the more general model. The new method provides a mechanism for pinpointing the effect that interobserver variability has on the ROC curve. It also allows for the adjustment of ROC curves for temporal variation and case mix, and provides a way to assess the incremental diagnostic value of a test. The new methodology is recommended because it substantially improves the ability to assess diagnostic tests using ROC curves.

Breast Neoplasms↗
PubMedDate not supplied

Testing for fetal pulmonary maturity: ROC analysis involving covariates, verification bias, and combination testing.

The lecithin/sphingomyelin ratio (L/S) and the measured value of saturated phosphatidylcholine (SPC), amniotic fluid determinations obtained to assess fetal pulmonary maturity, were evaluated with receiver operating characteristic (ROC) curve analysis. The effects of covariates on the ROC curves were analyzed with a regression methodology that took into account all the available data when constructing an ROC curve for each subgroup. To correct for verification bias the authors used a logistic regression analysis to model the probability of verification, thereby permitting correction for verification bias of a fully stratified data set in spite of small cell frequencies. They examined combination testing with prediction rules using prospective logistic modeling, including as variables test results and clinical features. The L/S was found to be significantly better than SPC for assessing fetal pulmonary maturity. For older gestational age the L/S and SPC performed better than for younger gestational age. Contamination of the specimen degraded the ROC curves. Correcting for verification bias did not influence the ROC curves significantly but changed the cutoff value of the test variable for any particular operating point. Prediction rules to evaluate combination testing showed that obtaining the SPC level in addition to the L/S ratio added no significant information compared with the L/S only. Including gestational age in the prediction rule of either test improved the prediction.

Bias↗
PubMedDate not supplied

Treatment of renal carcinoma: a phase III randomized trial of oral medroxyprogesterone (Provera), hydroxyurea, and nafoxidine.

Seventy patients with metastatic renal carcinoma were randomized to receive hydroxyurea, nafoxidine, or medroxyprogesterone (Provera) orally. Sixty patients were considered evaluable, with a response rate of 5% for medroxyprogesterone (one complete remission) and hydroxyurea (one partial remission) and a response rate of 16% for nafoxidine (two complete remissions and one partial remission). Differences in response rates and duration of survival were not statistically significant. The major toxicity observed with hydroxyurea was hematologic, and the major toxic effect of nafoxidine was an ichthyosis-like skin rash. Toxicity for medroxyprogesterone was minimal.

Clinical Trials as Topic↗
PubMedDate not supplied

Phase II study of vinblastine-CCNU, triazinate, and dactinomycin in advanced renal cell cancer.

A total of 133 patients with advanced or metastatic adenocarcinoma of the kidney were stratified according to performance status and time from initial diagnosis to recurrence and were then randomized to one of three different drug treatment arms or the crossover secondary treatment. The study drugs (combination vinblastine-CCNU and single-agent triazinate or dactinomycin) failed to provide any meaningful antitumor activity for these patients with advanced renal cell cancer.

Adenocarcinoma↗