A Monte Carlo Comparison of Tests for Multivariate Normality Based on Multivariate Skewness and Kurtosis.

The assumption of multivariate normality (MVN) underlies many common parametric multivariate statistical procedures, and numerous tests have been defined for testing the assumption. Among these tests, those based on concepts of multivariate skewness and multivariate kurtosis hold special interest since they appear to test for specific types of departures from MVN. This research uses Monte Carlo simulation to compare the performance of several MVN tests which are based on various definitions of multivariate skewness and kurtosis. Specifically, the tests are Mardia\u27s (1970) b\sb{\rm 1,p} and b\sb{\rm 2,p}, Small\u27s (1980) Q\sb1 and Q\sb2, and Srivastava\u27s (1984) b\sb{\rm 1p} and b\sb{\rm 2p}. Two main issues are addressed. First, Mardia\u27s tests are affine invariant, while those of Small and Srivastava are coordinate dependent. Conjectures are advanced regarding the conditions under which coordinate-dependent tests will perform better than affine-invariant tests and vice versa. A Monte Carlo experiment is constructed to evaluate these conjectures. It is concluded that neither coordinate-dependent nor affine-invariant tests can be eliminated from consideration, since each type is strongly superior to the other under certain circumstances. These circumstances pertain to whether or not those third- and fourth-order moments involving more than one variable in the coordinate system have normal or non-normal values. The second issue concerns the distributional dependency of skewness tests. It is conjectured, in particular, that skewness tests based on third-order moments (which includes all skewness tests considered here) are highly distributionally dependent, with this dependency being related to the same distributional characteristic that determines kurtosis. It is further conjectured that this dependency remains of importance asymptotically A Monte Carlo experiment is designed to evaluate these conjectures. Results confirm the dependency and that it is not simply a small sample problem. Based on this, it is concluded that skewness tests are not truly diagnostic; that is, they do not distinguish well between skewed and non-skewed distributions. In particular, skewness tests are likely to identify as skewed many non-skewed distributions with greater than MVN kurtosis; and they will fail to identify as skewed many skewed distributions with less than MVN kurtosis

Antithrombin III (AT) and recombinant tissue plasminogen activator (R-TPA) used singly and in combination versus supportive care for treatment of endotoxin-induced disseminated intravascular coagulation (DIC) in the neonatal pig

BACKGROUND: Disseminated intravascular coagulation (DIC) is a pathological disturbance of the complex balance between coagulation and anticoagulation that is precipitated by vascular injury, acidosis, endotoxin release and/or sepsis and characterized by severe bleeding and excessive clotting. The innately low levels of coagulation factors found in newborn infants place them at extremely high risk for DIC. Anecdotal reports suggest that either anticoagulant or fibrinolytic therapy may alleviate some of the manifestations of DIC. To test the hypothesis that replacement of both anticoagulants and fibrinolytics may improve survival and outcome better than either single agent or supportive care alone, we utilized a neonatal piglet model of endotoxin-induced DIC. METHODS: DIC was induced in twenty-seven neonatal pigs (7 to 14 days of age) by intravenous administration of E. coli endotoxin (800 μg/kg over 30 min). The piglets were divided into 4 groups on the basis of treatment protocol [A: supportive care alone; B: Antithrombin III (AT, 50 μg/kg bolus, 25 μg/kg per hr continuous infusion) and supportive care; C: Recombinant Tissue Plasminogen Activator (R-TPA, 25 μg/kg per hr continuous infusion) and supportive care; D: AT, R-TPA and supportive care] and monitored for 3 primary outcome parameters (survival time, macroscopic and microscopic organ involvement) and 4 secondary outcome parameters (hematocrit; platelet count; fibrinogen level; and antithrombin III level). RESULTS: Compared with supportive care alone, combination therapy with AT and R-TPA resulted in a significant improvement of survival time, hematocrit, AT level, macroscopic and microscopic organ involvement, p < 0.05. Compared with supportive care alone, R-TPA alone significantly reduced macroscopic organ involvement and AT alone increased AT levels. CONCLUSION: The findings suggest that combining AT, R-TPA and supportive care may prove more advantageous in treating the clinical manifestations of DIC in this neonatal pig model than either single modality or supportive care alone

Use of the emergency department for less-urgent care among type 2 diabetics under a disease management program

Abstract Background This study analyzed the likelihood of less-urgent emergency department (ED) visits among type 2 diabetic patients receiving care under a diabetes disease management (DM) program offered by the Louisiana State University Health Care Services Division (LSU HCSD). Methods All ED and outpatient clinic visits made by 6,412 type 2 diabetic patients from 1999 to 2006 were extracted from the LSU HCSD Disease Management (DM) Evaluation Database. Patient ED visits were classified as either urgent or less-urgent, and the likelihood of a less-urgent ED visit was compared with outpatient clinic visits using the Generalized Estimating Equation methodology for binary response to time-dependent variables. Results Patients who adhered to regular clinic visit schedules dictated by the DM program were less likely to use the ED for less urgent care with odds ratio of 0.1585. Insured patients had 1.13 to 1.70 greater odds of a less-urgent ED visit than those who were uninsured. Patients with better-managed glycated hemoglobin (A1c or HbA1c) levels were 82 times less likely to use less-urgent ED visits. Furthermore, being older, Caucasian, or a longer participant in the DM program had a modestly lower likelihood of less-urgent ED visits. The patient's Charlson Comorbidity Index (CCI), gender, prior hospitalization, and the admitting facility showed no effect. Conclusion Patients adhering to the DM visit guidelines were less likely to use the ED for less-urgent problems. Maintaining normal A1c levels for their diabetes also has the positive impact to reduce less-urgent ED usages. It suggests that successful DM programs may reduce inappropriate ED use. In contrast to expectations, uninsured patients were less likely to use the ED for less-urgent care. Patients in the DM program with Medicaid coverage were 1.3 times more likely to seek care in the ED for non-emergencies while commercially insured patients were nearly 1.7 times more likely to do so. Further research to understand inappropriate ED use among insured patients is needed. We suggest providing visit reminders, a call centre, or case managers to reduce the likelihood of less-urgent ED visit use among DM patients. By reducing the likelihood of unnecessary ED visits, successful DM programs can improve patient care.</p

Evaluation of The Federal Bureau of Prisons protocol for selection of which hepatitis C-infected inmates are considered for treatment

The Federal Bureau of Prisons limits hepatitis C therapy to those inmates with certain biochemical abnormalities. To evaluate this protocol, an analysis was done on data collected on hepatitis C infected inmates in the Louisiana Department of Corrections. A quality assurance database of hepatitis C infected inmates evaluated in the Louisiana Department of Corrections was reviewed for liver biopsy and laboratory results. Patients were compared as to whether they would have been biopsied under the Federal Bureau of Prisons protocol and if there were histologic differences between those who would and those who would not have been biopsied. Of 490 inmates biopsied, 26% (129) had an alanine aminotransferase level between one and two times the upper limit of normal without other biochemical abnormalities. If treating stages 2-4, 48% of these would qualify for treatment (15% if treating stages 3-4). There was no statistical difference between this group and either the group with an alanine aminotransferase level between one and two times the upper limit of normal and with other laboratory abnormalities or the group with an alanine aminotransferase level greater than or equal to two times the upper limit of normal and without other abnormalities. In the Louisiana Department of Corrections, the Federal Bureau of Prisons protocol was neither sensitive nor specific enough at identifying those that should be considered for hepatitis C therapy

Use of the emergency department for less-urgent care among type 2 diabetics under a disease management program

[[abstract]]Background: This study analyzed the likelihood of less-urgent emergency department (ED) visits among type 2 diabetic patients receiving care under a diabetes disease management (DM) program offered by the Louisiana State University Health Care Services Division (LSU HCSD). Methods: All ED and outpatient clinic visits made by 6,412 type 2 diabetic patients from 1999 to 2006 were extracted from the LSU HCSD Disease Management (DM) Evaluation Database. Patient ED visits were classified as either urgent or less-urgent, and the likelihood of a less-urgent ED visit was compared with outpatient clinic visits using the Generalized Estimating Equation methodology for binary response to time-dependent variables. Results: Patients who adhered to regular clinic visit schedules dictated by the DM program were less likely to use the ED for less urgent care with odds ratio of 0.1585. Insured patients had 1.13 to 1.70 greater odds of a less-urgent ED visit than those who were uninsured. Patients with better-managed glycated hemoglobin (A1c or HbA1c) levels were 82 times less likely to use less-urgent ED visits. Furthermore, being older, Caucasian, or a longer participant in the DM program had a modestly lower likelihood of less-urgent ED visits. The patient's Charlson Comorbidity Index (CCI), gender, prior hospitalization, and the admitting facility showed no effect. Conclusion: Patients adhering to the DM visit guidelines were less likely to use the ED for less-urgent problems. Maintaining normal A1c levels for their diabetes also has the positive impact to reduce less-urgent ED usages. It suggests that successful DM programs may reduce inappropriate ED use. In contrast to expectations, uninsured patients were less likely to use the ED for less-urgent care. Patients in the DM program with Medicaid coverage were 1.3 times more likely to seek care in the ED for non-emergencies while commercially insured patients were nearly 1.7 times more likely to do so. Further research to understand inappropriate ED use among insured patients is needed. We suggest providing visit reminders, a call centre, or case managers to reduce the likelihood of less-urgent ED visit use among DM patients. By reducing the likelihood of unnecessary ED visits, successful DM programs can improve patient care