**Re: Design of Experiments Using Subgroup Data**

Do you mean that for each experimental run, you are collecting multiple measurements?

If this is the case, this "subgroup" would consist of experimental repeats. Repeats are multiple measurements taken during a single setup of an experimental run. (If the experimental conditions are changed then at a later time are recreated as a new setup, this is called a replicate).

As a general practice, replicates are better than repeats because you are more likely to be able to duplicate experimental results from replicated experiments.

With repeats, the typical method is to calculate the mean and standard deviation of each subgroup. Perform the analysis on the mean to determine the usual information on main effects and interactions. Calculate the log of each standard deviation, then perform a similar analysis on the log(StDev). Look for factors that will significantly reduce the log(StDev) in order to minimize variation.

This is even more effective when used with an outer array that deliberately induces variation into the repeats.