1. The problem statement, all variables and given/known data I have to design an experiment with 3 factors. One factor has to be quantitative with at least 3 levels. One Qualitative with at least 3 levels. And the last one can be either quant/qual with at least 2 levels. My question is in regards to coding the variables. For example, and Im not sure this is correct, one of my quantitative factors is age groups. 10-20,21-30, 31-40,41-50. How would I code this using dummy variables? 2. Relevant equations 3. The attempt at a solution Since these are age groups it seems that coding my variable using x1 x2 1 1 0 0 1 0 0 1 with respect to the age groups is more of a qualitative approach. What I wish to do is make the coded variable be an interval taking into account a persons age. Not just ok, you are in group 1 because u are 15, but rather, your respective interval is x. Sorry I forgot most of my statistics info and I Hope this makes sense. Thanks.