In a recent article (Physical Therapy, March 1989), Jensen and Di Fabio described an intraclass correlation coefficient (ICC), type (3,1) = 0.37,1 that was calculated by using the diagnosis (a grouping category) variance as the numerator (Tab. 1). They used this coefficient as an index of reliability for a series of five measurements performed on each of 31 subjects. As such, this coefficient cannot be compared with those presented by others (ie, Tredinnick and Duncan2). The explanation is as follows. The variance version of reliability portrayed in the physical therapy literature represents the variance attributable to subjects divided by an appropriate representation of the total variance.… Kris Jensen, PT, Sports Medicine Physical Therapy, Supervisor. Richard P Di Fabio, PhD, PT, Director of Physical Therapy, Univ of Wisconsin Hospital & Clinics, Clinical Assistant Professor of Rehabilitation Medicine, Univ of Wisconsin School of Medicine, E3/211, 600 Highland Ave, Madison, WI 53792.