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At least 1,117 records · Page 62Linked to original sources
PubMed1995

Logistic regression with incompletely observed categorical covariates--investigating the sensitivity against violation of the missing at random assumption.

Missing values in the covariates are a widespread complication in the statistical inference of regression models. The maximum likelihood principle requires specification of the distribution of the covariates, at least in part. For categorical covariates, log-linear models can be used. Additionally, the missing at random assumption is necessary, which excludes a dependence of the occurrence of missing values on the unobserved covariate values. This assumption is often highly questionable. We present a framework to specify alternative missing value mechanisms such that maximum likelihood estimation of the regression parameters under a specified alternative is possible. This allows investigation of the sensitivity of a single estimate against violations of the missing at random assumption. The possible results of a sensitivity analysis are illustrated by artificial examples. The practical application is demonstrated by the analysis of two case-control studies.

ABO Blood-Group System↗
PubMed1993

Confidence limits for hazardous concentrations based on logistically distributed NOEC toxicity data.

This paper deals with the calculation of Hazardous Concentrations of toxic substances from small sets of laboratory toxicity data, e.g., NOECs. A procedure due to Van Straalen and Denneman, as adapted from Kooijman (case n = 1), in which one seeks a concentration that protects 95% of the biological species is modified to account for the uncertainty in the estimates. New constants are obtained by simulation. These allow the calculation of the one-sided 95% left confidence limit of the Hazardous Concentration, from the mean and standard deviation of a sample of (laboratory) toxicity data. This 95% confidence limit is always lower than the 95% certainty value calculated with the Kooijman (n = 1)/Van Straalen method. The authors also derive constants to calculate a one-sided 50% confidence value, that overpredicts as often as it underpredicts. This value may be used as a median guess of the Hazardous Concentration. It will always be higher than the 95% certainty value of the Kooijman (n = 1)/Van Straalen method. However, by using the 50% value, one runs the risk of protecting substantially less than 95% of the biological species.

Confidence Intervals↗
PubMed1989

Organ procurement in children--surgical, anaesthetic and logistic aspects.

To cover the need in paediatric organ transplantation, every potential donor should be considered as a multi-organ donor. Successful transplantation may be performed with kidneys retrieved from very young infants, even anencephalic neonates if the en-bloc technique using both kidneys is used. Regarding the liver, paediatric donors can be accepted from one month of age while livers harvested from older children and even young adults can be transplanted into small children after ex-vivo reduction of the size of the graft. Multi-organ procurement from the same donor provides valuable organs if the anaesthetic management of the donor is appropriate. Active transplant programs needs international cooperation which is made possible by the organ exchange organizations.

Adolescent↗
PubMed2000

[Effect of logistic and medical emergency resources on fatal outcome of severe trauma].

122 cases of patients who died in sequel of an accident (recruitment period 1993/94, mean ISS 40 +/- 19) in reach of air rescue base Dresden, Germany, were examined. Data were assessed from autopsy protocol and the protocol of the physician who treated on scene. We analyzed the time course of the emergency, the scheduled emergency medical service and the quality of prehospital diagnosis and therapy by the emergency team. The mean response time was 8.1 +/- 5.9 min, the mean distance between EMS bases und incident location 5.9 +/- 5.7 km. In 94.4% of all cases a mobile intensive care unit--with an emergency physician as crew member--was on scene, in 5.6% a paramedic car. Air rescue by helicopter, including an emergency physician, was performed only in 8.7% of all cases although a helicopter was available in 54% of all accidents. Mechanisms of injury were traffic accident (71.4%), fall (14.3), 5.9% accident on building site, shot and stab injuries (5.9%) and burns (1.7%). 82 patients reached the emergency room alive (67.2% mean ISS 37 +/- 18). Only 26% of all patients were transported directly to a level I trauma center. Mean survival time of all 122 patients was 146 +/- 30.4 h. Severe head injury described by autopsy protocol was diagnosed on scene in 82%. Preclinical treatment was:intubation and ventilation (63%), O2 insufflation (17.4%), no specific treatment (19.6%). Severe thoracic trauma was diagnosed in 54%. Preclinical treatment was:intubation and ventilation (64.8%), O2 application (18.8%), no specific treatment (16.2%). Severe thoracic trauma with hemato-pneumothorax (n = 26) was recognized by the emergency physician in 65.6%, specific therapy (application of chest drain) was performed in 7.1%. Preclinical diagnosis rates concerning abdominal trauma were 29% and 27.8% in case of unstable pelvis fracture. Hemorrhagic shock related to these injuries was found in 44.2%, mean resuscitation volume applicated in these cases was 960 +/- 610 ml. Typical faults in diagnosis and treatment were underestimating of severe trunk trauma and non-consistent use of invasive treatment procedures. Primary transport of the severely injured patient to a level I trauma center by helicopter was performed only rarely.

Adult↗
PubMed1998

[Operation of multidisciplinary, interventional 0.5 Tesla magnetic resonance tomograph. Technical and logistic problems and initial clinical results].

Multidisciplinary usage of a MRI system with a superconducting 0.5-T magnet (Signa SP, General Electric) with a vertical gap suited for diagnostic and therapeutic interventions raises complex problems. The MR equipment, including a special localizing system and the instruments for diagnostic and therapeutic interventions, is described. Before putting the system into operation tests were necessary to check MR compatibility of various materials and instruments and to build some auxiliary equipment. We report on the coordinating activities of the radiologist in the context of MR use by different medical specialities. Within the course of 12 months, 428 examinations/interventions of different kinds were carried out, among them 75 functional examinations of the spine or of joints, 31 diagnostic biopsies, 23 cerebral biopsies, and 23 operations. The special design of the Signa SP allows the whole scale of functional examinations, up to complete neurosurgical interventions, in the sitting position and under nearly real-time imaging control.

Equipment Design↗