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Biomedical subjects

E Somoza

Publications and source records attributed to E Somoza.

At least 19 recordsLinked to original sources
PubMed1992

Diagnostic tests and information theory.

Our previous article showed that the discriminating properties of most diagnostic tests in medicine can be characterized by assuming that tests separate disordered and nondisordered individuals into two overlapping, normal distributions with different means and standard deviations. In this article, we explore the relationship between this way of describing diagnostic tests and the reason that clinicians use them: to gain information about their patients and to reduce diagnostic uncertainty.

Diagnosis, Differential↗
PubMed1992

Comparing diagnostic tests using information theory: the INFO-ROC technique.

We continue our examination of diagnostic tests that are used to assign individuals to one of two mutually exclusive categories, those having or not having a particular disorder. Our last article showed how the information yielded by a test depends on the choice of cutoff and on the patient's pre-test probability of having the disorder. In this article, we demonstrate a method of optimizing a test's information yield that allows us to determine which of several tests gives the most information. Our technique allows us to compare a test's performance with that of a perfect diagnostic test.

Computer Simulation↗
PubMed1992

Balancing risks and benefits: another approach to optimizing diagnostic tests.

In our last two articles, we showed that one can quantify the reduction in uncertainty that results from diagnostic testing, an insight that allowed us to describe a method for optimizing the performance of a test by choosing a cutoff that maximizes its information yield. Although minimizing uncertainty is an important feature of diagnostic testing, there are many situations in which diagnostic tests are most appropriately used to balance risks and benefits associated with the various possible courses of action available to a clinician. This article shows how tests can be used to maximize the "expected utility" associated with a clinical decision.

Humans↗
PubMed1991

"Biological markers" and psychiatric diagnosis: risk-benefit balancing using ROC analysis.

Although the clinical interview retains a central role in psychiatric diagnosis, recent research has suggested that "biological markers" may ultimately increase the precision of clinicians' nosologic and therapeutic decisions. Evaluating and operationalizing diagnostic tests require mathematical techniques that reflect the tests' essential features and limitations, and that guide clinicians in particular clinical situations. In this article we describe a technique that combines signal detection theory and utility-based decision theory, and apply the technique to published data in which sleep architecture was used as a biological marker for depression. We show how outcome utilities influence the optimum REM latency cut-off and show how this relationship is influenced by the prevalence of depression in the population being tested. We also make specific calculations of the practical limits that must be imposed on uncertainties in utilities to operationalize a diagnostic test for a specific clinical situation.

Biomarkers↗
PubMed1991

A computerized system for measuring time perception in human subjects.

We describe an integrated computerized approach to the design, execution and recording of time perception experiments in human subjects. The program is menu driven and runs on an IBM-compatible microcomputer. The method is easy to use, non-obtrusive to the subjects, and flexible enough to allow the investigator to design studies with a wide range of experimental protocols and study parameters. The fact that the results do not depend on proctor bias or subject-proctor interactions are additional advantages. The technique was applied to study the effects of prompt positive feedback on the time perception of normal human subjects who undergo training. The results of this study are reported.

Adult↗
PubMed1991

Neuropsychiatric decision making: designing nonbinary diagnostic tests.

Most diagnostic tests used in medicine, science, and technology are nonbinary: they are based on quantification of a variable that has a range of possible values. In this article, the authors describe how such tests are designed and characterized. They shall use the concepts developed here in future articles that describe how diagnostic techniques are operationalized for clinical settings.

Blood Platelets↗
PubMed1991

ROC curves, test accuracy, and the description of diagnostic tests.

Clinicians can gain an enhanced understanding of the role of diagnostic tests once they are familiar and comfortable with the descriptions of test performance provided by receiver operating characteristic (ROC) analysis. This article explores the ways that ROC methods quantify test accuracy and describes how ROC methods characterize the distributions of test outcomes in study populations.

Humans↗
PubMed1991

ROC curves and the binormal assumption.

Previous articles in this series have described how receiver operating characteristic (ROC) graphs provide comprehensive graphic representations of the diagnostic performance of non-binary tests and have explained how one constructs "trapezoidal" ROC graphs in which discrete cutoff points are plotted and connected with line segments. In this article, we describe a set of mathematical assumptions that permit the generation of a continuous, smooth ROC curve for a given diagnostic test. These assumptions permit us to characterize a test's performance using a small number of parameters and also to explore properties of diagnostic tests. In this article, we describe a set of mathematical assumptions that can be used to link receiver operating characteristic (ROC) curves to the underlying distribution of values of the diagnostic variable being measured. We will illustrate these assumptions using a diagnostic test that distinguishes alcohol abusers from normal consumers of alcohol and abstainers.

Alcoholism↗
PubMed1990

Optimizing REM latency as a diagnostic test for depression using receiver operating characteristic analysis and information theory.

New diagnostic techniques must be evaluated for their intrinsic accuracy and for their applicability to particular patient groups in specific clinical settings. Using receiver operating characteristic (ROC) analysis and concepts from information theory, we have developed a new mathematical and graphical method that can evaluate, compare, and optimize the performance of diagnostic tests for any value of disorder prevalence. Our analytic method is appropriate to any test that sorts disordered from nondisordered subjects using a continuous or nonbinary diagnostic variable; its characterization of the fundamental properties of such tests thus has important implications for the evaluation and optimization of diagnostic modalities used by clinicians in all medical specialties. We demonstrate our method using published data from five studies that used sleep architecture as a "biological marker" for depression. Our analysis confirms that REM latency is comparable to the dexamethasone suppression test in its ability to discriminate depressed from control subjects. For each of the five studies, we show how optimal REM latency cut-off times may be selected so that diagnostic information yield is maximized, and we compare the ability of each study to detect depressed subjects in populations where the prevalence of affective disorder can be specified.

Adult↗
PubMed1990

Do serum dexamethasone levels improve the DST?

Some investigators have reported that dexamethasone suppression test (DST) accuracy might be improved by incorporating dexamethasone concentrations ([dex]) into test results. Using receiver operating characteristic methods, we evaluated data from four studies in which cortisol and dexamethasone levels were measured simultaneously at one or more times after drug ingestion. We compared DST accuracy using cortisol alone with various diagnostic indices incorporating [dex]. In none of the 21 comparisons did the [dex] factor enhance diagnostic performance.

Depressive Disorder↗
PubMed1990

Introduction to neuropsychiatric decision making: binary diagnostic tests.

This is the first in a series of articles that provide a guide to the understanding and effective use of diagnostic tests in clinical and research endeavors. In this article, we briefly describe some general properties of diagnostic tests. We then focus our attention on binary diagnostic tests, i.e., tests that have only two outcomes, positive or negative. Even though most medical literature assumes that all diagnostic tests are binary, truly binary tests are actually quite rare. Studying them, however, provides a convenient way to familiarize ourselves with important decision-making nomenclature.

Alzheimer Disease↗
PubMed1989

Assessing improvements in the dexamethasone suppression test using receiver operating characteristics analysis.

This article demonstrates methods by which receiver operating characteristics (ROC) analysis may be used to evaluate and improve the Dexamethasone Suppression Test (DST). ROC indices provide a description of nonbinary diagnostic tests that is independent of any particular cutoff and that allows investigators to use rigorous mathematical methods for selecting cutoffs and assessing overall performance. In this study, ROC analyses of previously published data suggest that (1) the accuracy of the DST might be improved by using a 0.5-mg oral steroid dose; (2) incorporation of dexamethasone serum levels does not improve the performance of the DST; and (3) the serum cortisol level used to define "no suppression" (or DST "positivity") should be varied to take into account diagnostic alternatives, prior probability of affective disorder, and the clinical goal for performing the test (e.g., maximizing utility, increasing information).

Depressive Disorder↗
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↗