DoE: Design of experiments

Times when researchers faced the optimization of processes by sequentially changing one variable at a time are long gone. The systematic design of experiments (DoE) began with the early work of R. Fisher in 1935, and was mainly developed during the 50's and 60's. Names such as Box, Wilson, Hunter, Davies or Taguchi stand as the fathers of what is currently a mature discipline in which mathematics are applied for the efficient and time-saving planning of experiments in almost any experimental science. With the help of commercially available software, there is no excuse for any researcher not to use this methodology in his/her daily experimental work.


The Design of Experiments (DoE) covers actually a plethora of techniques aimed at rationalizing the set up of experiments. However, any DoE technique shares the following basic concepts: 

Factor: every single variable that can have an influence in the experiment (time, temperature, pressure, ...).
Level: discrete value of a Factor within the experimental domain (eg, t= 10s or 3600s; T=273K or 373K).
Response: value of the variable that we are measuring during the experimental setup (eg, a yield in a chemical reaction or the stability of en emulsion).
Main Factors: changes in the Response of a system that can be directly linked to the changes in the Levels of one of the Factors.
Interactions: changes in the Response of a system that can be explained only by the combination of two or more Factors. First order interactions involve two main factors. Second order interactions involve three main factors, etc.

Two of the most used basic DoE techniques, the Factorial Design and the Mixture Design are covered in separate posts in the blog.

If you're considering optimizing your productivity by using DoE, I highly recommend taking a basic course. A one-week training is enough to get the basics of DoE and start planning your own experimental work. Get some commercial software too. If you're just an occasional user consider some of the free DoE programs available on the net, such as GOSSET.  If you're serious about DoE, and are looking for a program with a neat interface, great graphic output and contextual help, one of my favorites is DESIGN EXPERT (you can download a 30 days free trial version of the program).