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J C Peirce

Publications and source records attributed to J C Peirce.

22 records · Page 2Linked to original sources
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Integrating stratum-specific likelihood ratios with the analysis of ROC curves.

Data used to construct receiver operating characteristic (ROC) curves and to calculate the area under the curve (ROC AUC) can be used to derive stratum-specific likelihood ratios (SSLRs) with their 95% confidence intervals (95% CIs). The purpose of this study was to determine whether useful information can be obtained by adding SSLRs to the analysis of ROC curves. The authors analyzed four previously reported sets of data: 1) serum creatine kinase (SCK) for diagnosing acute myocardial infarction (AMI) in the coronary care unit (CCU); 2) SCK in the evaluation of chest pain in the emergency center (EC); 3) four predictor variables in the diagnosis of strep throat; and 4) the ordinal assessment of computed tomographic (CT) images. Use of SCK in the CCU produced four strata that had posttest probabilities that were highly discriminating, whereas SCK in the EC resulted in only two strata with limited discriminating ability. In either study the cutpoint at which the SSLR changed from less than to greater than 1.0 was higher than the reported upper normal for the test, thereby quantitating spectrum bias. The maximum number of strata of predictor signs and symptoms for strep throat was three rather than the five used in previous studies. With a larger sample size or pooling, four strata could probably be developed. With CT images, "definitely normal," "probably normal," and "questionable" were collapsed to one negative stratum. "Probably abnormal" became the true "questionable" stratum and "definitely abnormal" was the only positive stratum. The authors conclude that additional useful information is obtained by deriving stratum-specific likelihood ratios as part of the analysis of an ROC curve.

Humans↗
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The effectiveness of implementing the weight-based heparin nomogram as a practice guideline.

OBJECTIVE: To determine the effectiveness of the nomogram in a community hospital that implemented it as a practice guideline. DESIGN: A nonexperimental, retrospective time series. SETTING: A 600-bed community teaching hospital and regional referral center in Phoenix, Ariz. PATIENTS: The study population included 591 consecutive patients with venous thromboembolism, treated over a 5-year study period. METHODS: During this period, the weight-based heparin nomogram was adapted into a preprinted order sheet and distributed to the hospital wards. The main outcome variables were the time to achieve a therapeutic activated partial thromboplastin time and the rate of bleeding complications. RESULTS: Voluntary implementation of the nomogram steadily increased, reaching 94%. Comparison of the periods before and after 50% implementation demonstrated an increase in initial heparin dose (1185 vs 1420 U/h, P < .001), a decrease in time to achieve therapeutic activated partial thromboplastin time (19.6 vs 11.8 hours), a decrease in the variance of this parameter (25 vs 4 hours, P < .001), and no change in bleeding rates. The proportion of patients achieving a therapeutic activated partial thromboplastin time within 24 hours decreased from 97% to 86% when the results from our previous randomized controlled trial (efficacy) are compared with the present results (effectiveness). CONCLUSIONS: The weight-based heparin nomogram was well accepted by clinicians at our institution and led to more aggressive heparin dosing and improvements in intermediate outcomes, without increasing bleeding. Mitigation of benefit is likely to occur when practice guidelines are moved from the realm of efficacy research into clinical practice. Therefore, the effectiveness of such measures requires monitoring.

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