Charlie Brown and Statistics: An Exchange-Reply

To the Editor.— We would like to carry Dr Kraemer's "Peanuts" analogy one step further. Suppose the team statistician uses a method of rating players that is dependent on the number of times at bat. For players who have been on the team all year, the rating system will be a practical means of comparison, but it will strike out when applied to the brilliant player newly arrived from the farm team in midseason or batters who missed part of the season due to injury. Such has been the story with k. It has been used extensively as a measure in clinical studies, and as long as prevalences are consistently high, it is a consistent measure of the instrument reliability. But when it is extended to population studies, or used in clinical studies in which prevalences of specific diagnoses vary greatly, interpretation of k values must be made cautiously. Actually, Dr Kraemer claims