The following article is from IOL Horizons back in 2009.
I suspect some of you will have seen it, if you haven’t or, if you have never come across The Lemon Theory related to managing risk in adventurous activities I urge you to read it.
Also see this Peer Belaying Technical Note from AALA , this outlines the pros and cons of different belay methods. A little drier but another essential read for anyone working with climbing groups.