The empirical accuracy of uncertain inference models

Uncertainty is a pervasive feature of the domains in which expert systems are designed to function. Research design to test uncertain inference methods for accuracy and robustness, in accordance with standard engineering practice is reviewed. Several studies were conducted to assess how well various methods perform on problems constructed so that correct answers are known, and to find out what underlying features of a problem cause strong or weak performance. For each method studied, situations were identified in which performance deteriorates dramatically. Over a broad range of problems, some well known methods do only about as well as a simple linear regression model, and often much worse than a simple independence probability model. The results indicate that some commercially available expert system shells should be used with caution, because the uncertain inference models that they implement can yield rather inaccurate results

Iron supplements inhibit zinc but not copper absorption in vivo in ileostomy subjects

Background: Iron supplements may inhibit intestinal zinc and copper uptake because these elements may compete for binding to a transporter molecule (divalent metal transporter 1) that is located on the apical side of the small intestinal epithelium. Objective: We quantified the interaction between different amounts of administered iron and the absorption of zinc and copper in humans. Design: Eleven subjects with an ileostomy [mean (±SD) age: 55 ± 9 y] ingested a stable-isotope-labeled zinc and copper solution containing 12 mg Zn (66Zn and 67Zn) and 3 mg Cu (65Cu) in the presence of 0, 100, or 400 mg Fe as ferrous gluconate on 3 respective test days. Subsequently, 1 mg 70Zn was injected intravenously. Subjects collected ileostomy effluent and urine for 24 h and 7 d, respectively. Zinc status and true zinc absorption were calculated from the urinary excretion of the zinc isotopes. Apparent copper absorption was calculated from ileostomy effluent excretion of the orally administered copper isotopes. Results: Zinc status did not differ significantly between the 3 iron doses. Mean (±SEM) zinc absorption was significantly higher in the absence of iron than with the concomitant ingestion of 100 or 400 mg Fe (44 ± 22% compared with 26 ± 14% and 23 ± 6%, respectively; P < 0.05), whereas zinc absorption did not differ significantly between the 100- and 400-mg Fe doses. Apparent copper absorption was 48 ± 14%, 54 ± 26%, and 53 ± 7% in the presence of 0, 100, and 400 mg Fe, respectively, and did not differ significantly between the 3 iron doses. Conclusion: Oral iron therapy may impair zinc absorption and thus zinc status in a dose-independent fashion but does not affect copper absorption