Nested Orthogonal Arrays
  Orthogonal Arrays allow us to test various levels of each factor and balance the different factors so that we can estimate interactions as well as first order effects. There is a trade-off between how well we can sample different levels of each factor and how many interactions we are able to estimate. This paper describes one method to mitigate this trade-off. This method will allow us, with n observations, to sample n levels of each factor and minimize the correlation between the estimates of first order terms and their interactions. 
Joel Atkins and David B. Zax
stat.ME