I'm going to conduct experiment with 7 products. One subject can evaluate no more than 3 products. The ultimate goal is to compare all 7 products to each other (let say, on means) and rank them. So, full factorial design leads to 35 groups of products (with 3 products in each group) that is too much. I need to reduce it to at least 10.
Can't wrap my mind how to do this. All software that able to generate orthogonal designs need at least two factors with two levels but it seems I have one factor (with 5 levels) or five factors (with 1 level)...
May be someone can advice totally different approach to reliable rank 7 products on means?