RT Journal
A1 Pingsmann, A.
A1 Freedman, Kevin B.
A1 Bernstein, Joseph
T1 Sample Size and Statistical Power
JF The Journal of Bone & Joint Surgery
JO The Journal of Bone & Joint Surgery
YR 2000
FD September 1
VO 82
IS 9
SP 1360
OP a
DO 
UL http://dx.doi.org/
AB 
In the article "Current Concepts Review. Sample Size and Statistical
Power in Clinical Orthopaedic Research" (81-A: 1454-1460, Oct. 1999),
Freedman and Bernstein refer to the Knee Society score as a continuous
variable when calculating necessary sample sizes.  However, this
is not true, as distinct numbers are given to certain levels of
performance or qualities examined; for example, unlimited walking
is given 50 points, walking more than ten blocks is given 40 points,
and walking five to ten blocks is given 30 points2.
This is similar to the system of school grades (A to F) or to the
Apgar score in obstetrics.