Figure 4.

Schematic example of an experimental design in which the samples are selected according to a full factorial design. Hypotheses are based on limited information (red dots) which is then used by a model to predict the response (blue space) for a combination of the different factors (arrows). Subsequent samples (red dots) are chosen according to a scheme where all factors of interest are varied simultaneously. First the maximum and minimum values for examined factors are selected including center point for both (left-hand side plot), followed by estimation of the center points for selected factors (middle figure). This allows for estimating factor directions (right-hand side figure), which facilitate the use and interpretation of multivariate statistical models. The important impacts from single factors and relations between factors can subsequently be estimated. As more data is collected the model becomes more precise.