Screening factors

Figure 9-24B. Packing factors (screen packing and random dumped packing). Used by permission of U.S. Stoneware Co. (now, Norton Chemical Process Products Corp.).

Screen Factor. Screen Factor, the ratio of passage time of a solution to that of a solvent in a screen viscometer(45),... 

Finding the mathematical model of the research subject is the lower level of a research objective. It is obligatory for a large number of problems. This obligation comes after the end of factor screening or after finding the optimum. The general form of the research subject mathematical form is ... 

Table 2.40 shows a complete design matrix by the method of random balance original data taken from normal population y0 y synthesized response to which values of effects were added and the phases of factor screening with corrected response y1 y11 ym and ylv and their standard deviations. 

Fig. 4. Schematic representation of yeast one-hybrid transcription factor screening. C. roseus cDNAs were cloned in a fusion with the GAL4-activation domain (GAL4-AD) in yeast/E.coli shuttle vector pACTII. Yeast reporter strains carrying a tetramer of the cis-acting elements of interest (indicated in the figure with 4xbait) were transformed with the cDNA library and selected for transformation and reporter gene activation on medium lacking leucine and histidine, respectively...

The objective of a factor screening experiment is to investigate, efficiently and effectively, the factors of a system that possibly may be important to its performance and to identify those factors that have important effects. Once the important factors have been identified from the screening experiment, the experimenter will typically move the region of experimentation from the initial location towards one more likely to contain the optimum. The method of steepest ascent (Myers and Montgomery, 2002, Chapter 5) is the procedure most widely employed for this activity. Finally, once near the optimum, the experimenter will usually conduct one or more experiments in order to obtain a fairly precise description of the response surface and an estimate of the optimum conditions. 

For purposes of factor screening, it is usually sufficient to identify the main effects of the important factors and to obtain some insight about which factors may be... 

The sparsity of effects principle (see Box and Meyer, 1986) makes resolution III and IV fractional factorial designs particularly effective for factor screening. This principle states that, when many factors are studied in a factorial experiment, the system tends to be dominated by the main effects of some of the factors and a relatively small number of two-factor interactions. Thus resolution IV designs with main effects clear of two-factor interactions are very effective as screening... 

Projection Properties of Factorial Designs for Factor Screening... 

Cheng, S. W. and Wu, C. F. J. (2001). Factor screening and response surface exploration (with discussions). Statistica Sinica, 11, 553-604. 

Ghosh, S. (1979). On single and multistage factor screening procedures. Journal of Combinatorics, Information and System Sciences, 4, 275-284. 

Ghosh, S. and Avila, D. (1985). Some new factor screening designs using the search linear model. Journal of Statistical Planning and Inference, 11, 259-266. 

All factor screening designs are intended for situations in which there are too many factors to study in detail. If the number of factors is very large and/or each experimental run is very expensive, then it may be impractical to use even the Resolution III two-level designs of Chapter 1, which allow all main effects to be estimated. In such cases, it might be useful to run experiments with fewer runs than there are factors to try to identify a small number of factors that appear to have dominant effects. 

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