*Geek Box: 2 x 2 Factorial Design

*Geek Box: 2 x 2 Factorial Design

A 2 x 2 factorial design is a specific trial design which tests two interventions in the one study sample. In a 2 x 2 design, there are two independent variables, and a dependent variable. The ‘factor’ is the independent variable. Each factor may have different levels.

Therefore, in a “2 x 2” design, there are two independent variables [factors] and two levels of each factor. In this study, we have two factors: texture and processing. Within each factor, we have two levels: soft and hard texture, and minimally and ultra-processed.

There are a number of results you can get from this type of design, including main effects and/or interaction effects. The ‘main effect’ is an outcome related to the levels of the factor. In the example of this study, there could be a main effect of food texture if texture had an effect at each level of processing. There could also be a main effect of processing if we found a difference between levels of processing that was independent of texture. You could also have an ‘interaction effect’, e.g., it could be that the combination of the texture and processing significantly affects outcomes.

The present study also utilised a cross-over design, meaning that each subject served as their own control and consumed each of the four test meals. Cross-over designs are useful for nutrition interventions, given that there may be distinct inter-individual differences in metabolism and responses to a particular exposure [either diet or supplement].

Factorial designs are helpful trial designs which allow for different independent variables [the factors] to be included in a single study, so they are an efficient way of doing research. They also allow for interaction effects to be examined, which is important in determining whether differences in treatment may be explained by variations between the factors and levels examined.