Changes In Tolerance Levels Research Articles

One-sided Continuous Tolerance Limits and their Accompanying Sample Size Problem

Tolerance limits are those limits that contain a certain proportion of the distribution of a characteristic with a given probability. 'They are used to make sure that the production will not be outside of specifications' (Amin & Lee, 1999). Usually, tolerance limits are constructed at the beginning of the monitoring of the process. Since they are calculated just one time, these tolerance limits cannot reflect changes of tolerance level over the lifetime of the process. This research proposes an algorithm to construct tolerance limits continuously over time for any given distribution. This algorithm makes use of the exponentially weighted moving average (EWMA) technique. It can be observed that the sample size required by this method is reduced over time.

The Continuous Non-parametric Tolerance Limits

Tolerance limits form an interval within which at least a certain proportion of a population lies with a given confidence level. Usually, they are used to make sure that the production will not be outside of specifications. For non-normal populations, non-parametric tolerance limits are constructed at the beginning of the process. Being calculated just one time, these tolerance limits cannot reflect changes of tolerance level over the lifetime of the process. This article proposes a non-parametric method of constructing tolerance limits continuously over time. A simulation study is conducted to compare the average lengths and standard deviations of the tolerance intervals for both the snapshot and the continuously constructed non-parametric tolerance limits.

Tolerance limits as a continuous assessment tool

Non-parametric tolerance limits are used to make sure that production will not be outside specifications for non-normal populations. They are constructed usually at the beginning of a process run. These limits do not reflect changes of tolerance level over the lifetime of the process. This article proposes the continuous assessment of process tolerance. The procedure utilizes the exponentially weighted moving average method and provides evidence of process tolerance over the lifetime of the process. The resulting tolerance limits are shown to be narrower on average and exhibit considerably lower variability than the non-parametric limits commonly used. The sample size required for these tolerance limits can also be reduced by a considerable amount over time.

Tolerance limits as a continuous assessment tool

Non-parametric tolerance limits are used to make sure that production will not be outside specifications for non-normal populations. They are constructed usually at the beginning of a process run. These limits do not reflect changes of tolerance level over the lifetime of the process. This article proposes the continuous assessment of process tolerance. The procedure utilizes the exponentially weighted moving average method and provides evidence of process tolerance over the lifetime of the process. The resulting tolerance limits are shown to be narrower on average and exhibit considerably lower variability than the non-parametric limits commonly used. The sample size required for these tolerance limits can also be reduced by a considerable amount over time.

Response of soil bacterial communities pre-exposed to different metals and reinoculated in an unpolluted soil

Changes in tolerance levels of soil bacterial communities pre-exposed to different metal concentrations and then reestablished in an unpolluted soil were examined during a one year incubation period using the thymidine incorporation technique. The study was performed with a sterilized agricultural soil, which was reinoculated with bacteria extracted from soils previously contaminated with high doses of Zn, Cu or Cd, and from an unpolluted soil. Bacteria pre-exposed to metal addition initially exhibited a greater tolerance than those non-pre-exposed. The microbial communities responded to the absence of metals in the reinoculated soil with a rapid decrease in community tolerance, losing most of the acquired tolerance (70–90%) within the first week. After that no changes in community tolerance were detected. Thus, a long-lasting effect of the original community tolerance of the inoculum was detected even 12 months after the metal stress was removed. At this time there was still a dose-response effect left since higher tolerance levels were usually found in soils with higher tolerant inoculum. Changes in tolerance levels over time showed similar trends, irrespective of which metal the bacterial communities were initially tolerant.

Problems in obtaining a description of the evolution of dimethoate resistance in Danish houseflies (Musca domestica)

AbstractData on the evolution of a polygenically determined resistance to dimethoate, in populations of houseflies on Danish farms, were examined in order to see whether useful information about the processes involved could be obtained. Examination of the variance of tolerances in samples of flies suggested that there was considerable genetic variability for resistance before dimethoate was first used, but provided no other information. Before examining estimates of log LD50 (LLD50), the relationship between LLD50 and the log weight of the flies assayed was investigated in an experiment in Denmark, and the standard error of LLD50 estimates was estimated. Examination of LLD50 estimates (adjusted for log weight) provided evidence of substantial migration of flies between farms, which produced large and unpredictable changes in tolerance levels on individual farms, and prevented extraction of further useful information from the data. However, it was concluded that even had migration been negligible, the data would not have provided information suitable for the construction of models of the evolution of this polygenically determined resistance. This conclusion is likely to hold for most existing data. Alternative approaches towards obtaining models of the evolution of polygenically determined resistances are suggested.