BOOKS OF RtfiDIfGS - PAHO/WHO

?Vol. XVIII. No. 2. Sttilluleareiltte
- 49 -
strongly related to age and Lage was
selected ats a partitioniiiig variable, thenl
secon(idary diagnosis would not aippear
powerful in subsequent clustering.
Groups were then generated bas i on
the most appropriate variable, that is, the
one that .et as nainy of the criteria
specified above as possible. In particular, it
1) exhibited a significant reduction in variance
relative to iiost ot the other variablles,
2) created a manageablie ni tilher of>groil>ps
based on the relatively smaill iinlmer ol
values of the independeit variable, and 3)
createtl groups whiose ueaiits were signilicantly
dlitierent. Also. grotups Ibruied were
homogeneoxns troni a clinical perspective.
Once each Mlajor Diagnostic Category
was initially pairtitioled inito suilgrotips
based on the valiues of an independent varíable,
a decision was nmade whether or not
to further subdivide each saubgroup based
on any of the other available variables or to
end the partitioning process by treating
thenm as terminal groups. The statistical
basis for this decision was deterniined by a
set of stopping r ules. For any given gronup,
the partitioning ceased when etiher one of
the following conditions was mnet:
1. The grrotip was not large enoughl to
Warrunt anIother classificatiom, tlhat is, whllvl
the ilnliilber of oihserfiltion>is in the groiup
was less thani 100.
2. None of the varialbles relducedl uniexplainil
variation I)v at Ieast 1%, or
((TSS -'I WSSQ)/TSSQ)*100 < 1 per
cent.*
Otherwise, the group was fuirther subdivided
according to the criteria discuissed
previously tor generating new, sulbgroups.
In some cases, however, the process was
terminated tor nonstatistical reasons regarding
overall inanageability (e.g. inaintaining
a low number of total groups) or
medical interpretability.
* This I per cent I>ouid was increased ii certain
Major Diagnostic Categories.
DC; :()NST'I'(:'i'ION
Tlhis grotu),ping process resulted i¡ tihe
lormatio, oí' :383 finai grolups or I)CG.s
each defutied by somie set of the tollowing
patient attributes: primary diagnosis, see-
' ondiny diagnosis, primary surgical procedure.
secontlary surgical procedure, age,
and in one case, clinical service aiea. While
other variables such as sex, tertiary diagnosis
or surgical procediure were
examtined, they were not imnild to be significiant
iii explaining ouitput utilization. A list
of these grotups with a brieft narrative descriptioei
of their contents appears in the
Ap)l)elctlix. A more ctiip)lete spetcification
can be obtained fromn tlie Health Care
Financing Administration.'
The DRGs vary considerably in their
structure across the iMajor Diagnostic
Categories. Some Major Diagnostic
Categories are not further subdivided,
such as Category 35, Hemorrhoids, in which
no variable demonistraited a sufficient efttct
in further explaining outpitt uti lization. On
the other hand, Appendicitis, Category 46,
is ftirther subdivided on, the basis of
specific primary diagnosis and the presence
ot a secondary diagnosis. This restilts
in 4 DRGs: appendivitis (without
peritontitis) and without a secondary diagnosis,
appendicitis (without peritonitis)
with a secoudary diagnosis, appeidicitis
(with peritonitis) without a secondary
diagnosis, and appendicitis (with
peritonitis) with a secondary diagnosis.
This symmetric breakdown suggests that
the effects of primary. diagnosis and the
presence of a seconldary diagnosis are additive
in nature. Major Diagnostic Category
76, Fractures, has the nmost complex structure,
resulting in 13 DRGs, indicating both
the importance and interaction of 4 variables:
primary diagnosis, secondary diagnosis,
prinmary surgical procedure and age.
It should also be noted that when variables
are h.ghly correlated, very often only
one applears in the classification for a
specilic mnajor category. Asn extrieme exampie
of this is Major Diagnostic Category 36,
Hypertrophy of Tonsils aud AdeMoid,