BOOKS OF RtfiDIfGS - PAHO/WHO

Vol. XVIII, No. 2, Suppletiment
- 61 -
and region's average length of stay (AV.
ERBAGE LOS DIFFER) and indlicate to
what extent this dit'ference can be attributed
to DRG-specific average length of
stay or the ai (DIFFER DUE TO LOS), the
case mix of its patients or the PU (DIFFER
DUE TC CASE MIX), and the combination
of the 2 or their interaction (INTER-
ACT DIFFER).
The separation ot' the diltereiice intO
these comiponents is hased ou the
technique described by Kitagawa,'4 brietly
dlescribed here fi)r the reader's convenlience.
It' ; auld A reprepresent tie averalige
length of stay for the ¿th iistitution and the
region, respectively, then
a, = Pj aJ;, = 1 .... 33 (DRGC) (4.3)
A = PJAJ. j = ..... 383 (DRG) (4.4)
The difference between a; and A can be
expressed as
DRGC APPLICATIONS
hospital and the region not accounted for
hy the LOS difference (column 10) or the
case mix difference (columnn 11).
The utilization of the report lies in interpreting
the differences observed between
an indivtdual institution and the set of institutions
or region as a whole. For example,
consider Hospital 4, the largest with
41,643 cases (column 2). Its average length
of stay was one of the longest, 7.479 days
(column 3) or 0.708 days longer than the
region (column 9). This diftterence can be
attribhltedl in varying degrees to the following
componients: 1) dileretices iii case
composition or case mix; 2) differences in
case-specific average lengths of stay; and 3)
differences attributed to the interaction of
case mix and case-specific average lengths
of stay. With respect to the first component,
if the hospital's case mix had been treated
at the region's average length of stay per
DRG, Hospitail 4's average length of stay
would have been 6.96 days (column 5), for
a difference of 0. 188 days over the region
(column 11). On the other hand, if the case
a - A = P (a, -A,)+ Aj (p - P) + (a - A (p - P
AVERAGE
LOS
DIFFER
,,., j , . / . -
DIFFER DUE
TO LOS
for i = 1 .. , 383 (DRG).
I'This .may be rewritten as
DIFFER DUE
TO CASE
MIX
k-A=( A Pa",,- PA,)+ (1 Ap p,,- A, P) + C (aU-) (pi,-P,) (4.6)
.'i j j j J
for j = ,...,383 (DRG),
.from which we note that the first 3 differ-
1:ences are computed by subtracting the
region's average length of stay from the
m,,,ores in columnis 3 through 5. The
interaction component is the residual or
the amount of the difference between the
qr~
INTERACT
DIFFER
(4.5)
mix were standardized or all institutions
were treating the same types of patients,
Hospital 4 would have had an average
lengtlh of' stay of 7.320 days (coluann 4),
about a half day (column 10) longer than
the region. Moreover, relative to the