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Biomedical subjects

L Hothorn

Publications and source records attributed to L Hothorn.

9 recordsLinked to original sources
PubMed1998

Testing strategies in multi-dose experiments including active control.

Inferential test strategies for multi-arm trials are adapted or proposed for the special situation when more than one dose of a test treatment, placebo and active control(s) are compared. This includes between doses, dose-placebo and dose-active-control comparisons. The procedures refer to situations when detailed comparisons make sense only if the sensitivity of the trial has been shown, for example, if a dose-response relationship or a difference between active control and placebo has been established. Split strategies, hierarchical (assuming an order restriction among doses) or linked procedures are introduced. In linked procedures, equivalence to the active control will be established only if the dose is also shown to be effective as compared to placebo. All the inferential procedures control the experimentwise error rate in the strong sense for the respective sets of null hypotheses considered.

Alkylating Agents↗
PubMed1998

Teleradiology: results of a questionnaire of German radiologists.

A questionnaire was sent by mail to 4400 radiologists (i.e. to at least 1000 radiological institutions). The response rate was about 5%. The results showed that 47% of respondents felt well informed about teleradiology, 49% not enough and 3% not at all. Image and report transfer as well as interfaces to reference databases, educational applications, technical quality surveillance and product support (maintenance) were considered to be increasingly important areas. Smaller institutions (1-3 doctors) judged expert consultation as more important than bigger institutions. Standardization, system stability and data security were demanded as well as guidelines, for example concerning the linking of report and image, correct documentation and required image quality. Technically most demands can be fulfilled today but this technology is not yet commonly included in teleradiology systems.

Attitude of Health Personnel↗
PubMed1994

Biostatistical analysis of the micronucleus mutagenicity assay based on the assumption of a mixing distribution.

The in vivo micronucleus assay can be analyzed by comparing the number of micronuclei (MN) of several dose groups with those of a control group. In several publications, difficulties arose in estimating a suitable distribution for MN, even in the untreated historical control groups. Mitchell et al. described the presence of a subpopulation of more susceptible responders. Based on this assumption of such a subpopulation, score tests were used for the mixing distribution of responders and nonresponders (behavior same as in untreated control animals) within the dose groups. The power behavior of these tests was characterized with a simulation study. The advantage of score tests can be shown, even in the practical and important guideline case of only five animals per group.

Animals↗
PubMed1994

Multiple comparisons in long-term toxicity studies.

Several multiple comparison procedures (MCPs) are discussed in relation to the specific formulation of type I and type II errors in toxicity studies and the typical one-way design control versus k treatment/dose groups. Examples for these MCPs are: the standard many-to-one MCP (Dunnett's procedure), sequential rejection modifications, closed testing procedures, many-to-one MCPs with an ordered alternative hypothesis, procedures based on the assumption of a mixing distribution of responders and nonresponders, and MCP's for multiple end points.

Hazardous Substances↗
PubMed1991

Tumor induction in a rat model for ureterosigmoidostomy without evidence of nitrosamine formation.

Twenty rats were randomized into a vesicosigmoidostomy and an unoperated control group. In both groups the 24 hour excretion of secondary amines, nitrate, nitrite and nitrosamines was measured before and after gavage of proline and nitrate, piperazine and nitrate, N-nitrosoproline, mono-N-nitrosopiperazine. The urinary nitrosamine concentrations were not significantly different between both groups neither before nor after application of the several substances. Thirty rats were randomized into two vesicosigmoidostomy groups with and without antibiotic coverage and an unoperated control group. After ligation of distal rectum and mesosigmoid the rectosigmoids were removed. No significant concentrations of volatile nitrosamines could be measured in the rectosigmoid contents of the three groups. One hundred and twenty rats randomized into three groups following vesicosigmoidostomy received the potential nitrosamine antidotes sodium-2-mercaptoethane sulfonate or sodiumpentosan-polysulfate or acted as controls. 12/118 (10.2%) developed adenomas and 25/118 (21.2%) adenocarcinomas at the vesico-colonic anastomosis with no significant differences between the three groups concerning tumor incidence or mortality. The results show that colon carcinomas occur in a rat model for ureterosigmoidostomy without evidence for thus induced nitrosamine formation. This and the missing effect of nitrosamine antidotes suggest that other factors than nitrosation must be responsible for colon carcinogenesis following urinary diversion via intestine.

Adenocarcinoma↗