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E Somoza

Publications and source records attributed to E Somoza.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1982

Biochemical findings in a case of parkinsonism secondary to brain tumor.

Neuropathological and biochemical studies were performed in a patient with craniopharyngioma and a long history of parkinsonism. Morphological examination revealed atrophy of the substantia nigra without Lewy bodies. Both th caudate and putamen nuclei showed moderate loss of large cells with glial proliferation. There was a notable decrease in dopamine and its metabolites and a reduction in norepinephrine content in both the caudate and putamen nuclei. Less consistent changes were found in serotonin and amino acid levels. Dopamine receptors, evaluated as 3H-spiperone binding sites, were unchanged in the putamen but decreased to 30% of control values in the caudate. The findings suggest that parkinsonism was caused by the brain tumor, which damaged both the presynaptic dopaminergic nigrostriatal neurons and the postsynaptic dopamine receptors.

Aged↗
PubMed1982

Inhibition of leu-enkephalin binding by neuroleptics.

The binding of leu-enkephalin to synaptosome-enriched fractions prepared from rat whole brain has been measured in the presence and absence of haloperidol, chlorpromazine and chlozapine. All three neuroleptics produced a dose-dependent inhibition of the binding with inhibition constants of 33.7, 89.6, and 34.2 microM for haloperidol, chlorpromazine, and clozapine, respectively, and resulted in parabolic Hill plots suggestive of multiprocess modes of action rather than simple competitive or noncompetitive interactions. Except for the case of haloperidol, the inhibition constants are comparable to brain tissue levels of neuroleptics after chronic administration. This suggests that neuroleptic treatment may block a significant fraction of endogenous leu-enkephalin from reaching its CNS receptors.

Animals↗
PubMed1981

Clozapine inhibition of metenkephalin binding to synaptosome-enriched fractions of rat whole brain and hippocampus.

Clozapine has been found to inhibit the binding of [3H]met-enkephalin to synaptosome-enriched fractions prepared from rat whole brain and hippocampus in a Tris-buffered media without added ions. The IC50 value for hippocampus is 28.5 microM. The inhibition constant for whole brain (41.0 microM) was found to be slightly larger than the corresponding value for chlorpromazine, which was measured under similar experimental conditions.

Animals↗
PubMed1977

Effect of di-n-propylacetate on the 'binding of GABA to synaptosome-enriched fraction of rat cerebral cortex.

The effect of di-n-propylacetate (DPA) on the 'binding' of gamma-aminobutyric acid (GABA) to a synaptosome-enriched fraction of rat cerebral cortex has been examined using differential centrifugation and double-isotope liquid scintillation spectrometry. DPA at 10(-4) M caused a slight decrease in GABA binding. This effect could explain in part the in vivo anticonvulsant and behavioral effects of this drug when administered to animals in high systemic doses.

Aminobutyrates↗