Factorial Design

The Factorial Design dialog creates a factorial or fractional factorial design. Typically a researcher begins a designed experiment by generating a design, which is a data frame indicating the combinations of experimental variable levels at which to take observations. The researcher then measures some outcome for the indicated experimental variable combinations and record this by adding a new column to the design data frame. The data may then be analyzed using ANOVA or other techniques.

The basic factorial design contains all possible combinations of the variable levels, possibly replicated and randomized. A fractional factorial design excludes some combinations based upon what model effects are of interest.

To create a factorial design

Choose Statistics __image\arrow5.gif Design __image\arrow5.gif Factorial. The dialog shown below appears.

The Factorial Design dialog requires some knowledge of S-PLUS language syntax. An example is illustrated in the dialog shown below, followed by the resulting data set.

__image\facdsgn.gif

The Factorial Design dialog has the following options:

Levels

Enter a vector of the number of levels for the factors in the design.

Number of Replications

Specify the number of times the complete design should be replicated. The default value is 1.

Fraction

Optionally, specify the definition for the fraction desired in a fractional factorial design.

Factor Names

Optionally, specify names for the factors

Row Names

Optionally, specify names to use for the rows of the design. The default is 1:nrows, where nrows is the number of observations in the design.

Randomization

Randomize Row Order Select to randomize the order of the rows in the design.

Restricted Factors Optionally, specify a vector (either numeric or character) naming some factors (columns) in the design which shouldn't be scrambled.

Save In

Enter the name for the object in which to save the results of the analysis. If an object with this name already exists, its contents are overwritten.

Related programming language functions

fac.design, randomize