B. S. Everitt's excellent article on cluster analysis (Journal, February 1972, p. 143) provides a much needed warning of the difficulties involved in the use of this technique. One way, however, of avoiding at least some of the pitfalls of this method needs to be stressed. This is the application of what is perhaps the universal panacea for scientific flights of fancy, namely, common sense. Common sense is particularly applicable to the choice of variables to be measured, and, of course, to the problem of naming the groups once they have been found. The use of mathematical techniques without the concurrent application of common sense is one of the greatest traps for the unwary and the overenthusiastic.