Morbidity and disability.

The reader will observe that our customary "P’s and Q’s" column has been changed to a "P’s and R’s" commentary this time, in keeping with the general theme of disability in this issue. When mortality is being studied, survival (’P) and death rate (Q) are among the measures commanding attention. When morbidity is being assessed, P becomes event-free survival, the inverse of some event-rate R for morbid events of particular outcome-interest. Some of the unique methodologic issues which arise in morbidity measurement have been addressed in an earlier Journal articleI and examples of morbidity abstracts occur regularly now in these pages.