Replications, statistical methodology

A designed or active experiment is based on using general methodological concepts such as regression and correlation analysis, analysis of variance, randomization, optimal use of factor space, successive experimenting, replication, compactness of information, statistical estimates, etc. 

One major deviation from the typical toxicity test methodologies was that field replicates were used for toxicity testing in lieu of the standard laboratory replication (z. e., one replicate per station rather than 5). This modification was made a priori in order to maximize the number of stations at the expense of statistical power within the available project resources. 

Reduction refers to efforts to minimise the number of animals used during an experiment, as well as the prevention of unnecessary replication of previous experiments. To satisfy this requirement, statistical design of experimentation (SDE) methodology and other mathematical calculations of statistical power are employed to determine the minimum number of animals that must be used to get a statistically significant experimental result. 

Sometimes, experiments are repeated with a particular set of levels for all the factors to check the statistical validation and repeatability by the replicate data. This is called replication. To get rid of any bias, allocation of experimental material and the order of experimental runs are randomly selected. This is called randomisation. To arrange the experimental material into groups, or blocks, that should be more homogeneous than the entire set of material is called blocking. So, when experiments are carried ont these things should be remembered. There are several methodologies for design of experiments. Some DOE methods are presented below. 

An example of the time constraints in depth profile analysis is noted in high precision depth profiling of dopants as is reqnired in the semiconductor industry. In addition to the reqnirement of primary ion beam stability, these typically employ the collection of at least three replicate profiles per analysis site. A minimum of three is stipulated as this represents the minimnm value needed in carrying out any form of statistical analysis. Only throngh snch methodologies can a dose precision of better than 1% be derived (this is assnming that the substrate contains sufficient dose to provide the needed connting statistics). 

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