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D Mossman

Publications and source records attributed to D Mossman.

54 records · Page 3Linked to original sources
PubMed1989

Maximizing diagnostic information from the dexamethasone suppression test. An approach to criterion selection using receiver operating characteristic analysis.

Receiver operating characteristic analysis yields indices of diagnostic performance that permit innovative mathematical descriptions and comparisons of diagnostic tests whose results are distributed over a range of possible outcomes. We employed data from seven published studies to demonstrate how ROC analysis may be used to characterize the discriminative properties of the dexamethasone suppression test (DST). We also used an intrinsic property of test results--their ability to reduce diagnostic uncertainty--to select cortisol cutoff levels with the highest information content for each of the DST studies. These cutoffs often differ from original authors' definitions of nonsuppression. The information-maximizing cortisol levels vary depending on pretest estimates of the prevalence of depression or melancholia and vary among studies. Receiver operating characteristic analytic techniques provide important tools for a full description of the DST. Future studies should use receiver operating characteristic methods to select cortisol cutoffs and to assess the test's overall performance.

Binding, Competitive↗
PubMed1989

Evaluation and optimization of diagnostic tests using receiver operating characteristic analysis and information theory.

We describe a mathematical technique and an associated computer program for comparing, evaluating and optimizing diagnostic tests. The technique combines receiver operating characteristic (ROC) analysis with information theory and cost-benefit analysis to accomplish this. The program is menu driven and highly interactive; it generates 13 possible user-determined ASCII disk files which can be easily converted to graphs. These graphs allow the user to make detailed comparisons among various diagnostic tests for all values of disorder prevalence, and also provide guidelines for cut-off selection in order to optimize tests. These techniques are applied to three published studies of the enzyme screening assay for diagnosis of infection with the HIV virus. We show how graphs produced by this program can be used to compare and optimize these diagnostic tests. The program is written for an IBM-compatible microcomputer running on a DOS operating system.

Clinical Laboratory Techniques↗
PubMed1988

The dexamethasone suppression test and depression. Approaches to the use of a laboratory test in psychiatry.

The dexamethasone suppression test has undergone unprecedented study among the biologic tests proposed for clinical use in psychiatry. Since the 1970s, its study has involved hundreds of reports and thousands of patients. Although important technical aspects of the test appear to be well accepted and validated, additional information is needed regarding the pharmacokinetics of dexamethasone. Marked interindividual differences in plasma dexamethasone suggest that performance of the test might be improved by factoring dexamethasone levels into test interpretations. There also may be advantages to the development of a modified test involving other exogenous and index steroids, such as monitoring corticosterone levels. Although it is too early to determine how ROC analysis will alter the clinical application of the test, some implications for methodology and data presentation are already clear. First, because the test is a diagnostic system with nonbinary outcomes, ROC analysis can augment traditional performance indices such as sensitivity, specificity, and positive predictive power. Second, ROC analysis will improve comparisons between the studies of different research groups and will help assess innovations in the application of the test. Third, ROC analytic techniques permit appropriate planning of sample size given estimates of the expected values of AUC that would be obtained from the studies. ROC theory thus promises to play an increasingly important role in the evaluation and future improvement of the dexamethasone suppression test and other biologic markers in clinical psychiatry. In conclusion, neither uncritical enthusiasm nor excessive skepticism is warranted about the use of the dexamethasone suppression test in clinical psychiatry. Evidence to date should encourage investigators to pursue refinement of the test or other tests of hypothalemic-pituitary-adrenal functioning to increase their accuracy and clinical utility.

Adrenocorticotropic Hormone↗
PubMed1988

The dexamethasone suppression test and depression. Approaches to the use of a laboratory test in psychiatry.

The dexamethasone suppression test has undergone unprecedented study among the biologic tests proposed for clinical use in psychiatry. Since the 1970s, its study has involved hundreds of reports and thousands of patients. Although important technical aspects of the test appear to be well accepted and validated, additional information is needed regarding the pharmacokinetics of dexamethasone. Marked interindividual differences in plasma dexamethasone suggest that performance of the test might be improved by factoring dexamethasone levels into test interpretations. There also may be advantages to the development of a modified test involving other exogenous and index steroids, such as monitoring corticosterone levels. Although it is too early to determine how ROC analysis will alter the clinical application of the test, some implications for methodology and data presentation are already clear. First, because the test is a diagnostic system with nonbinary outcomes, ROC analysis can augment traditional performance indices such as sensitivity, specificity, and positive predictive power. Second, ROC analysis will improve comparisons between the studies of different research groups and will help assess innovations in the application of the test. Third, ROC analytic techniques permit appropriate planning of sample size given estimates of the expected values of AUC that would be obtained from the studies. ROC theory thus promises to play an increasingly important role in the evaluation and future improvement of the dexamethasone suppression test and other biologic markers in clinical psychiatry. In conclusion, neither uncritical enthusiasm nor excessive skepticism is warranted about the use of the dexamethasone suppression test in clinical psychiatry. Evidence to date should encourage investigators to pursue refinement of the test or other tests of hypothalamic-pituitary-adrenal functioning to increase their accuracy and clinical utility.

Adrenocorticotropic Hormone↗
PubMed1988

United States v. Lyons: toward a new conception of legal insanity.

In United States v. Lyons (1984), the U.S. Fifth Circuit Court altered its definition of legal insanity to conform with recent recommendations of the American Bar Association and the American Psychiatric Association. This paper briefly reviews the social and legal context of the Court's ruling. The author then discusses the insanity defense's rationale and suggests an interpretation of the Court's new definition that should guide psychiatric testimony.

Cognition↗
PubMedDate not supplied

Intervals for posttest probabilities: a comparison of 5 methods.

BACKGROUND: Several medical articles discuss methods of constructing confidence intervals for single proportions and the likelihood ratio, but scant attention has been given to the systematic study of intervals for the posterior odds, or the positive predictive value, of a test. METHODS: The authors describe 5 methods of constructing confidence intervals for posttest probabilities when estimates of sensitivity, specificity, and the pretest probability of a disorder are derived from empirical data. They then evaluate each method to determine how well the intervals' coverage properties correspond to their nominal value. RESULTS: When the estimates of pretest probabilities, sensitivity, and specificity are derived from more than 80 subjects and are not close to 0 or 1, all methods generate intervals with appropriate coverage properties. When these conditions are not met, however, the best-performing method is an objective Bayesian approach implemented by a simple simulation using a spreadsheet. CONCLUSION: Physicians and investigators can generate accurate confidence intervals for posttest probabilities in small-sample situations using the objective Bayesian approach.

Bayes Theorem↗
PubMedDate not supplied

Comparing and optimizing diagnostic tests: an information-theoretical approach.

An ideal method for assessing performance of non-binary diagnostic tests would specify each test's optimal operating point and would tell a diagnostician which of many tests was the best one to use in a particular clinical situation. This article shows how information theory and receiver operating characteristic (ROC) analysis can be combined to evaluate and compare diagnostic tests at their optimum cutoffs once disease prevalence and test properties are specified. Though it is not appropriate for all clinical situations, the method can be used for most diagnostic tests whenever information is desired for its own sake or when reducing uncertainty is the goal of testing. The method also is appropriate in those situations where benefits and costs cannot be specified precisely enough to permit test optimization based on a balancing of anticipated goods and evils.

Diagnostic Tests, Routine↗
PubMedDate not supplied

Resampling techniques in the analysis of non-binormal ROC data.

The methods most commonly used for analyzing receiver operating characteristic (ROC) data incorporate "binormal" assumptions about the latent frequency distributions of test results. Although these assumptions have proved robust to a wide variety of actual frequency distributions, some data sets do not "fit" the binormal model. In such cases, resampling techniques such as the jackknife and the bootstrap provide versatile, distribution-independent, and more appropriate methods for hypothesis testing. This article describes the application of resampling techniques to ROC data for which the binormal assumptions are not appropriate, and suggests that the bootstrap may be especially helpful in determining confidence intervals from small data samples. The widespread availability of ever-faster computers has made resampling methods increasingly accessible and convenient tools for data analysis.

Bias↗
PubMedDate not supplied

Three-way ROCs.

Receiver operating characteristic (ROC) analysis traditionally has dealt with dichotomous diagnostic tasks (e.g., determining whether a disorder is present or absent). Often, however, medical problems involve distinguishing among more than two diagnostic alternatives. This article extends ROC concepts to diagnostic enterprises with three possible outcomes. For a trichotomous decision task, one can plot a ROC surface on three-dimensional coordinates; the volume under the ROC surface (VUS) equals the probability that test values will allow a decision maker to correctly sort a trio of items containing a randomly-selected member from each of three populations. Thus, the VUS summarizes global diagnostic accuracy for trichotomous tests, just as the area under a ROC curve does for a two-alternative diagnostic task. Information gain at points on the surface can be calculated just as is done for two-dimensional ROC curves, and investigators can thus compare three-way ROCs by comparing maximum information gain on each ROC surface.

Decision Making↗