Effects of Exposure Imprecision on Estimation of the Benchmark Dose

In regression analysis failure to adjust for imprecision in the exposure variable is likely to lead to underestimation of the exposure effect. However, the consequences of exposure error for determination of safe doses of toxic substances have so far not received much attention. The benchmark approach is one of the most widely used methods for development of exposure limits. An important advantage of this approach is that it can be applied to observational data. However, in this type of data, exposure markers are seldom measured without error. It is shown that, if the exposure error is ignored, then the benchmark approach produces results that are biased toward higher and less protective levels. It is therefore important to take exposure measurement error into account when calculating benchmark doses. Methods that allow this adjustment are described and illustrated in data from an epidemiological study on the health effects of prenatal mercury exposure.     

Historical controls and modern survival analysis

Comparison of observed mortality with known, background, or standard rates has taken place for several hundred years. With the developments of regression models for survival data, an increasing interest has arisen in individualizing the standardisation using covariates of each individual. Also, account sometimes needs to be taken of random variation in the standard group.Emphasizing uses of the Cox regression model, this paper surveys a number of critical choices and pitfalls in this area. The methods are illustrated by comparing survival of liver patients after transplantation with survival after conservative treatment.     

Transportnetzgestaltung für Paketdienstleister

Zusammenfassung  In diesem Beitrag entwickeln wir ein Hub-Location-Modell zur Bestimmung der Standorte von Hubs aus einer gegebenen Menge von Depots. Mit einer stufenf?rmigen Transportkostenfunktion erhalten wir die effiziente Kombination von Fahrzeugen bestimmter Typen von einem oder mehreren Verkehrstr?gern. Ferner berücksichtigen wir direkte Transporte und die Regellaufzeit der einzelnen Transporte. In Anlehnung an ein vorhandenes Transportnetz eines Paketdienstleisters demonstrieren wir die Anwendbarkeit des Ansatzes.

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Transportation network design for parcel service provider

Summary  In this paper we develop a hub location model to determine the locations of hubs from a given set of depots. Applying a stepwise transport cost function, we get the efficient combination of certain types of vehicles by one or more modes of transport. Furthermore, we consider direct transports and a maximum transit time. Based on an existing transportation network of a parcel service provider, the applicability of the model is shown.

     

Life Quality measures of smoking

The cost of smoking has three principal dimensions: money, reduced life expectancy, and diminished health. Each component can be quantified; all have an influence on the quality and duration of life. The combined influence can be evaluated using an aggregated social indicator, such as the Life Quality Index. It can be expressed in various ways, e.g. as an equivalent move to a nation or to a time with a lower level of the LQI, as an equivalent economic loss, or as an equivalent loss of life expectancy. To illustrate, the analysis is applied to Danish data on smoking; the cost for a typical pack-a-day habit is equivalent to a 57% reduction in personal income, 8.6 years loss of life expectancy, or a 4% drop in the Life Quality Index. These measures underscore the seriousness of smoking as a health hazard.     

ESTIMATION OF THE CONDITIONAL PROBABILITY OF TUBERCULOSIS GIVEN THE RESPONSE OF A MANTOUX TEST

For the planning of community tuberculosis, prophylaxis one must know the prevalence of tuberculosis (TB) infection as a function of response to the Mantoux intradermal tuberculin test; the standard test for indicating Mycobacterium TB infection. The skin induration size used to select individuals for prophylaxis must be chosen carefully, in view of the costs associated with carrying out and supervising such prophylaxis. The Mantoux test was used to obtain measurements on adolescents in metropolitan Victoria and on a small sample of adolescents with clinical TB. These data are employed to obtain estimates and to construct upper confidence bounds for the conditional probability of TB infection, given the level of Mantoux response. Two conservative methods are presented; one is ‘nonparametric’, the other ‘semiparametric’. The analyses indicate that for responses up to and including 13 mm, the probability of TB infection is less than.07 with ninety-five percent confidence.     

Developer autonomy in the FreeBSD open source project

Delegation of authority is the basic approach to coordination of work in FreeBSD, an open source software (OSS) project that develops and maintains an operating system. This essay combines a software engineering perspective with a knowledge creation perspective to discuss three central mechanisms in FreeBSD: (1) motivation, (2) quality control by frequent building, and (3) bugfixing by parallel debugging. It is argued that frequent building is the project’s key coordinating mechanism, and that build breakdowns play a constructive role in the processes of knowledge creation in FreeBSD.     

Product-limit estimators of the gap time distribution of a renewal process under different sampling patterns

Nonparametric estimation of the gap time distribution in a simple renewal process may be considered a problem in survival analysis under particular sampling frames corresponding to how the renewal process is observed. This note describes several such situations where simple product limit estimators, though inefficient, may still be useful.     

Prevalent cohort studies and unobserved heterogeneity

Lifetime Data Analysis - Consider lifetimes originating at a series of calendar times $$ t_{1} ,t_{2} , ldots $$ . At a certain time $$ t_{0} $$ a cross-sectional sample is taken, generating a...