Medical Decision Making

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at Society for Medical Decision Making Member Access on August 22, 2012 mdm.sagepub. .... Leonard Davis Institute of Health Economics, University of Penn-.
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Clinical Guidelines for Using Two Dichotomous Tests John C. Hershey, Randall D. Cebul and Sankey V. Williams Med Decis Making 1986 6: 68 DOI: 10.1177/0272989X8600600203 The online version of this article can be found at: http://mdm.sagepub.com/content/6/2/68

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Clinical Guidelines for Using Two Dichotomous Tests JOHN C. HERSHEY, PHD, RANDALL D. CEBUL, MD, SANKEY V. WILLIAMS, MD Building on the threshold model developed by Pauker and Kassirer for a single test, the authors describe a decision analytic model for two tests with dichotomous outcomes. The model includes ten decision strategies that differ depending on which tests are performed, whether the tests are performed together or in sequence, and the definition of a positivity criterion used to make the treatment decision when the test results disagree. Formulas derived from the model are used to compute the preferred option as a function of disease probability and to calculate test and test-treatment thresholds. General guidelines developed from the model can be used without calculation to identify relative preferences for alternative options and to predict threshold effects. Key words: decision analytic model; tests with dichotomous outcomes. (Med Decis Making 6:68-78, 1986) called &dquo;parallel testing,&dquo; or in sequence, which is called &dquo;series testing.&dquo;’ The clinician also must decide whether both tests or only one must be positive before treatment is administered. When there are two tests with dichotomous outcomes, there are ten distinct options (table 1). The purpose of this article is to describe a general decision analytic model to examine these ten options and to discuss general clinical guidelines for using two dichotomous tests. To illustrate how the approach introduced by Pauker and Kassirer can be extended to this more complex clinical situation, we have modified one clinical example in their original paper to include an additional test. Pauker and Kassirer described a patient with severe hypertension suspected of having vasculitis with renal involvement. The patient described here has the additional finding of recent skin lesions, but is in all other respects identical to the patient described by Pauker and Kassirer. Likewise, except for data related to a possible skin biopsy, we have used Pauker and Kassirer’s estimates for probabilities, risks, and benefits.

In 1980 Pauker and Kassirer described a formal analysis that has allowed clinicians to use a more rational, quantitative approach for a single test with a dicho-

outcome.&dquo; Beginning with a general decision for the test and treatment options, they identified two management thresholds based on pretest disease probability. The test threshold is the probability of disease below which therapy should be withheld without testing. The test-treatment threshold is the probability of disease above which therapy should be administered without testing. The test should be performed only if the disease probability is between the two thresholds. In many clinical situations, however, more than one test could be used to make the treatment decision, and it would be useful to extend Pauker and Kassirer’s approach to these situations. Doing so has proved difficult because there are many more options with multiple tests. When there is a single test with a dichotomous outcome, there are only three management options. When there are two tests with dichotomous outcomes, there are additional options that depend on whether one or the other test is to be performed first and on whether one or both tests are to be performed. When both tests are considered, there are still more options. The clinician must decide whether to perform the two tests together, which is tomous tree

CLINICAL EXAMPLE

Economics, the Department of Decision Sciences in the Wharton School, and the Section of General Medicine in the Medical School

55-year-old man has arthralgias, severe hypertenmm Hg), and renal failure (blood urea nitrogen, 90 mg/dl; creatinine 8 mg/dl). There is no history of renal disease, but for the past five years the patient has had hypertension treated with methyldopa and diuretics. Six months ago his

the University of Pennsylvania, Philadelphia, Pennsylvania. Accepted for publication July 2, 1985. Drs. Cebul and Williams are Henry J. Kaiser Family Foundation Faculty Scholars in General Internal Medicine. Supported in part by a grant from the National Science Foundation (SES82-18565), and by IBM. Address correspondence and reprint requests to Dr. Hershey: Leonard Davis Institute of Health Economics, University of Pennsylvania, Philadelphia, PA 19104.

renal function was normal. The fundi show Grade 3 hypertensive changes. The skin shows a few scattered petechiae, several urticarial lesions, and pigmented lesions that the patient says formerly were hives. The remainder of the physical examination is normal. The leukocyte count is 9,700 with 2% eosinophils and no leftward shift; hemoglobin is 14

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sion (blood pressure, 240/140

Received June 1, 1985, from the Leonard Davis Institute of Health

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