I keep remembering a conversation from when I studied for an MSc in Psychological Assessment many years ago. We were talking about the different types of validity a psychological test needs to have to be considered, um, valid – face, content, construct, concurrent, predictive, and impact and so on. Our professor asked us what tests we actually used at work. So we discussed the merits of OPQ, Myers Briggs, SDI and others, and when he came to me I said the only one I'd used of late was Belbin Team Roles, for training and development purposes.
“Oh yes” he said. “Every trainer's classic stand-by. It promotes discussion, a bit of navel-gazing, fills the gaps of a dozen different training sessions. But, of course, the real reason trainers love it is that it can be photocopied for free out the back of the book. It has what we like to call 'Xerox validity'”.