Joined: Mar. 2005
1) The sample would consist of all known intelligent designers (and so would exclude non-human animals on this planet, e.g., ants, beavers, etc.).
2) With respect to unqualified designers, the description of expected similarities has to be general enough to include different sorts of designers (e.g., painters, engineers, etc.). For the purposes of defining the general property "produces works that are similar to each other," "similarity" means "partial structural identity" (i.e., to be "similar" is to be "partially different and partially the same"). For example, two different models of BMW automobiles are similar, i.e., parts of them are the same and parts of them are different.
No. 2 could use some more work, but the main idea seems clear enough.