My understanding, Mr. Chair, and I'm learning as I go here, is that the makeup of the panel is determined through a somewhat collaborative process. It begins with contact with the office of the House leader, who in turn contacts counterparts, and then it's up to the whip in each party to identify potential members. The secretariat, for example, does not have input into who the panel members are; rather, it's determined through that combination of people I just described.
On October 25th, 2006. See this statement in context.