5.3. Choosing an experimental design
5.3.3. How do you select an experimental design?
18.104.22.168. Fractional factorial designs
|Screening designs are an efficient way to identify significant main effects||The term `Screening Design' refers to an experimental plan that is intended to find the few significant factors from a list of many potential ones. Alternatively, we refer to a design as a screening design if its primary purpose is to identify significant main effects, rather than interaction effects, the latter being assumed an order of magnitude less important.|
|Use screening designs when you have many factors to consider||Even when the experimental goal is to eventually fit a response surface model (an RSM analysis), the first experiment should be a screening design when there are many factors to consider.|
|Screening designs are usually resolution III or IV||
Screening designs are typically of resolution
III. The reason is that resolution III designs permit one to explore
the effects of many factors with an efficient number of runs.
Sometimes designs of resolution IV are also used for screening designs. In these designs, main effects are confounded with, at worst, three-factor interactions. This is better from the confounding viewpoint, but the designs require more runs than a resolution III design.
|Plackett-Burman designs||Another common family of screening designs is the Plackett-Burman set of designs, so named after its inventors. These designs are of resolution III and will be described later.|
|Economical plans for determing significant main effects||In short, screening designs are economical experimental plans that focus on determining the relative significance of many main effects.|