Fischer: Comparison of Cost Weight Proportions of Different Patient Classification Systems.

Z I M - Paper 13th PCS/E Florence Oct. 1997


Comparison of Cost Weight Proportions
of Different Patient Classification Systems

Wolfram Fischer

Zentrum für Informatik und wirtschaftliche Medizin
CH-9116 Wolfertswil SG (Switzerland)
http://www.fischer-zim.ch/


In: Proceedings of the 13th PCS/E International Working Conference. Florence 1997: 230-234.

Contents :
 •  Abstract
 •  Introduction
 •  Method and Material
 •  Results
 •  Discussion
 •  Conclusions
 •  References
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ABSTRACT

INTRODUCTION: To compare cost weights of different patient classification systems (PCS) the proportion of cost weights of pairs of patient groups are calculated in each system. The hypothesis being tested is: The proportion of cost weights of two case groups (diseases/procedures groups) classified by the same PCS is equal in all PCSs.

MATERIAL: Case groups of this theoretical study are: Simple hernia procedures, simple appendectomy, cholecystectomy (for patients < 65 years without complications and without comorbidities). The compared PCS are HCFA-DRG, AP-DRG, PMC, Disease Staging, HRG, German Case Groups, Austrian Diagnosis Groups (LDF).

RESULT: This study shows that the cost weight proportions of simple diseases with O.R. procedures vary in part considerably between the compared patient classification systems.

CONCLUSIONS: It seems to be necessary that cost weights are calculated for each country that is to say population. And: There have to be descriptions of what is included in a case group as a sort of product definition (e.g. ways of treatment and quality ranges).

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INTRODUCTION

Clinical information systems should be able to inform about the hospital production. A way often used to measure the treatment of patients is the use of cost weights of hospital case groups related to diagnoses and/or procedures from which case mix indices can be calculated.

In this paper I will present a comparison of cost weights from different patient classification systems. Because there is no common scale for cost weights (no common point "one") I have calculated proportions of cost weights of pairs of case groups in each PCS. The aim of this paper is to show if these proportions are the same in different PCSs.

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METHOD AND MATERIAL

The proportions of cost weights of different case groups should mirror the proportions of costs of the corresponding treatment. More explicit: If a cholecystectomy produces costs which are one and a half times higher than the costs of a hernia procedure, then the cost weights are expected to be in a proportion of 1.5 : 1 in each PCS.

For this theoretical study three diseases without comorbidities or complications for patients who are less than 65 years of age were chosen as test cases:
 
 

Case Group ICD-9-CM/1 ICD-9-CM/3
Operation of simple hernia 550.90 53.00
Simple appendectomy 540.9 47.0
Cholecystectomy laparoscopic 574.20 51.23
open (total) 574.20 51.22

Table 1: Tested Case Groups

 
 

As far as possible a difference was made between laparoscopic and open surgery:

The compared PCSs are:

The cost weights were derived from handbooks or using grouper software [8]. An exception were the weights of D.S.: In this system only diagnoses are used to group a hospital case; but to calculate weights additional information is used (especially procedures and age). [9]

In the following tables the differences are rounded to 5%.

To visualise the results the original (relative) cost weights of the test cases are drawn on a scale which begins at zero. On these figures you should not compare the absolute distances from zero but the proportions of these distances (i.e. not X2-X1, but X2/X1). The hypothesis is that these proportions should be equal in all PCSs.  
 


  +----------------------------------------------------------------------
  |    .    .    .    .    :    .    .    .    .    :    .    .    .    . PCS X 
  |    .    .    .    X1   :    .    .    .    .    :    .    .    .    .
  |    .    .    .    .    :    .X2  .    .    .    :    .    .    .    .
  |    .    .    .    .    :    .    .    .    .    :    .    .    .    .
  +----+----+----+----+----+----+----+----+----+----+----+----+----+----+
  0   0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9  1.0  1.1  1.2  1.3  1.4 
                                                               Cost Weight

Table 2: Visualisation of a Comparison

 
 

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RESULTS

This study shows that the cost weight proportions of simple diseases with O.R. procedures (simple hernia procedure, appendectomy, cholecystectomy) vary in part considerably between patient classification systems such as HCFA-DRG, AP-DRG, PMC, Disease Staging, HRG, German Case Groups, Austrian LDF.

From the following figures we can see e.g.: Using HCFA DRGs the cost weight of appendectomy is 45% higher than the cost weight for a simple hernia procedure. By using AP-DRG we obtain a cost weight which is only 20% higher. PMC weighs these cases nearly equally. Disease Staging considers appendectomy much more consuming than a simple hernia procedure (+55%).

Regarding the difference between cholecystectomy and appendectomy there is agreement in a great deal between HCFA-DRG, AP-DRG and PMC: The cost weights for cholecystectomy are only slightly higher (+10%, +5%, 0%). But studying now the values for length of stay (LOS) the statements differ considerably (laparoscopic cholecystectomy is 35% shorter than appendectomy in HCFA-DRG, 50% in AP-DRG, 65% in PMC. Disease Staging shows nearly the doubled values for cost weight and LOS of cholecystectomy. Attention: D.S. makes no difference between laparoscopic and open cholecystectomy.)

It is remarkable that the German and Austrian models have more or less clearly lower cost weights for (open) appendectomy compared to simple hernia procedure. This proportion is inverse in the US systems DRG and D.S.
 
 

HCFA-DRG
12.0
AP-DRG
12.0
PMC
5.0
D.S.
4.0
in % of HCFA-DRG
AP-DRG PMC D.S.
Simple Hernia Procedure Group
162
162
1203
GI27
s1.1
Weight
0.54
0.67
0.54
0.42
+25%
0%
-15%
Days
2.2
3
2.6
29%
+35%
+20%
HighTrim
11
9
-20%
Appendectomy Uncomplicated Group
167
167
1101
GI16
s1.1
Weight
0.79
0.81
0.58
0.64
0%
-25%
-20%
Days
3.6
4
2.9
49%
+10%
-20%
HighTrim
16
6
-65%
Laparoscopic Cholecystectomy Group
494
494
0604
HB07
s1.1
Weight
0.88
0.85
0.56
1.33
-5%
-35%
+50%
Days
2.4
2
1.0
94%
-15%
-60%
HighTrim
15
5
-65%
Total (open) Cholecystectomy Group
198
198
0601
HB07
s1.1
Weight
1.14
1.33
0.93
1.33
+15%
-20%
15%
Days
5.4
5
3.7
94%
-5%
-30%
HighTrim
24
17
-30%

Table 3: Comparison of American Cost Weights of Simple Diseases

 
 
 
 

Differences HCFA-DRG
12.0
AP-DRG
12.0
PMC
5.0
D.S.
4.0
HRG
2.0
GSG
'95
LDF
'97
Appendectomy
/
Hernia Proc.
Weight +45% +20%+5% +55% +40%-10% -33%
Days +65% +35%+10% +70% +64%-10% -40%
HighTrim +45% -35% +35% -5% -45%
Lap. Cholecystect.
/
Hernia Proc.
Weight +65% +25%+5% +220% +30% +170%
Days +10% -35% -60% +225% -10% +70%
HighTrim +35% -45% -5% +55%
Lap. Cholecystect.
/
Appendectomy
Weight +10% +5%0% +110% +30% +165%
Days -35% -50% -65% +90% +20% +200%
HighTrim -5% -15% +5% +130%
Lap. Cholecystect.
/
Open Cholecyst.
Weight -25% -35% -40% 0% -13% +115%
Days -55% -60% -75% 0% -36% +75%
HighTrim -40% -70% -20% +35%

Table 4: Differencdes of Cost Weight Proportions of Simple Diseases

 
 

 
 

  +----------------------------------------------------------------------------
  |    .    .    .    .Hrn :    .    .    .    .    :    .    .    HCFA-DRG  8 
  |    .    .    .    .    :    .    .  App    .    :    .    .    .
  |    .    .    .    .    :    .    .    .   ChL   :    .    .    .
  |    .    .    .    .    :    .    .    .    .ChO :    .    .    .
  +----------------------------------------------------------------------------
  |    .    .    .    .    :Hrn .    .    .    .    :    .    .    HCFA-DRG 12
  |    .    .    .    .    :    .    .   App   .    :    .    .    .
  |    .    .    .    .    :    .    .    .   ChL   :    .    .    .
  |    .    .    .    .    :    .    .    .    .    :    .ChO .    .
  +----------------------------------------------------------------------------
  |    .    .    .    .    :    . Hrn.    .    .    :    .    .    . AP-DRG 12
  |    .    .    .    .    :    .    .   App   .    :    .    .    .
  |    .    .    .    .    :    .    .    . ChL.    :    .    .    .
  |    .    .    .    .    :    .    .    .    .    :    .    .    .ChO
  +----------------------------------------------------------------------------
  |    .    .    .    .    :Hrn .    .    .    .    :    .    .    .    PMC  5
  |    .    .    .    .    :  App    .    .    .    :    .    .    .
  |    .    .    .    .    : ChL.    .    .    .    :    .    .    .
  |    .    .    .    .    :    .    .    .    .ChO :    .    .    .
  +----------------------------------------------------------------------------
  |    .    .    .    Hrn  :    .    .    .    .    :    .    .    .    D.S. 4
  |    .    .    .    .    :    .App .    .    .    :    .    .    .   
  |    .    .    .    .    :    .    .    .    .    :    .    .    .ChL
  |    .    .    .    .    :    .    .    .    .    :    .    .    .ChO
  +----+----+----+----+----+----+----+----+----+----+----+----+----+----+--
  0   0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9  1.0  1.1  1.2  1.3  1.4 
                                                               Cost Weight

Table 5: Comparison of Cost Weights of Simple Diseases: PCS from US

 
 
Legend: DRG:   PMC:   D.S.:
Hrn    Inguinal Hernia with Operation 162 1203 GI27/1.1
App Appendectomy uncomplicated 167 1101 GI16/1.1
ChL Laparoscopic Cholecystectomy 494 0604 HB07/1.1
ChO Open (total) Cholecystectomy 494 0601 HB07/1.1
 
 


  +----------------------------------------------------------------------------
  |    .    .    .    .    :    .    .   Hrn .    :    .      .    .    HRG  2 
  |    .    .    .    .    :    .    .    .    .    :   App   .    .    .
  |    .    .    .    .    :    .    .    .    .    :    .    .    .    .
  |    .    .    .    .    :    .    .    .    .    :    .    .    .    .  Cho
  +----+----+----+----+----+----+----+----+----+----+----+----+----+----+--
  0   0'1  0'2  0'3  0'4  0'5  0'6  0'7  0'8  0'9  1'0  1'1  1'2  1'3  1'4
                                     National Average Costs of Stay (1'000£)
                                         (Data from 1994/95 of 70 Hospitals)

Table 6: Comparison of Cost Weights of Simple Diseases: HRG (U.K.)

 
 
Legend: HRG:
Hrn   Hernia Procedures/Cat.4 f73 - Primary Repair of Inguinal Hernia
AppAppendix Procedures/Cat.3    f84 - Excision of Appendix
ChoBiliary Tract Procs/Cat.4 g13 - Total Cholecystectomy
 
 


  +----------------------------------------------------------------------------
  |    .    .    .    .    :    .   Hrn   .    .    :    . GSG-Case Groups'95 
  |    .    .    .    .    :    .    ApL  .    .    :    .    .    .    .
  |    .    .    .    .    :    .ApO .    .    .    :    .    .    .    .
  |    .    .    .    .    :    .    .    .    .ChL :    .    .    .    .    
  |    .    .    .    .    :    .    .    .    .    :  ChO    .    .    .
  +----+----+----+----+----+----+----+----+----+----+----+----+----+----+--
  0   0'5  1'0  1'5  2'0  2'5  3'0  3'5  4'0  4'5  5'0  5'5  6'0  6'5  7'0
                                         Points for Main Department in 1'000

  +----------------------------------------------------------------------------
  |    .    .    .    .Hrn :    .    .    .    .    :    .    .    .    LDF'97
  |    .    .    .    . ApL:    .    .    .    .    :    .    .    .    .
  |    .    .   ApO   .    :    .    .    .    .    :    .    .    .    .
  |    .    .    .    .    :    .    .    .    .    :    .  ChL    .    .
  |    .    .    .    .    : ChO.    .    .    .    :    .    .    .    .
  +----+----+----+----+----+----+----+----+----+----+----+----+----+----+--
  0        15'       30'       45'       60'       75'       90'      105'
                                                             Points in 1'000

Table 7: Comparison of Cost Weights of Simple Diseases: German and Austrian Case Groups

 
 
Legend: German: Austrian:
Hrn   Simple Hernia Procedure GSG 12.07   MEL 06.06 A
ApLLaparoscopic Appendectomy GSG 12.06MEL 06.01 A
ApOOpen Appendectomy GSG 12.05MEL 06.01 C
ChLLaparoscopic Cholecystectomy    GSG 12.04MEL 05.05 B
ChOOpen (total) Cholecystectomy GSG 12.03MEL 05.05 A

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DISCUSSION

The differences of cost weight proportions in different PCSs can be caused by:

It is striking that case groups with the same labels show such differences in their relative scoring. It is even more striking if one knows that the ways of treatment which go along with it are very routine.

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CONCLUSIONS

The consequences to be taken are:

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REFERENCES

[1] Fetter RB, Brand A, Dianne G [Eds.]: DRGs, Their Design and Development. Health Administration Press, Ann Arbor 1991: 341 pp.

[2] Fischer W: Patientenklassifikationssysteme zur Bildung von Behandlungsfallgruppen im stationären Bereich - Prinzipien und Beispiele (Patient Classification Systems for Grouping Hospital Cases - Principles and Examples). BSV and Z/I/M, Bern and Wolfertswil 1997: 514 pp, cit. p. 453ff.

[3] PRI: Patient Management Categories, Release 5.0. The Pittsburgh Research Institute, Pittsburgh, w/o year: Attachment A.

[4] Gonella JS, Hornbrook MC, Louis DZ: Staging of Disease. A Case-Mix Measurement. In: JAMA 1984(251)5:637-44. Gonella JS, Louis DZ, Marvin EG: Disease Staging: Clinical Criteria. Forth Edition, MEDSTAT Systems, Ann Arbor 1994: 834 pp.

[5] Sanderson HF, Anthony P, Mountney LM: Healthcare Resource Groups - Version 2. Winchester 1996 (NCMO: Occasional Paper No. 6): 15 pp. National Casemix Office. HRG - Health Resource Groups; Definitions Manual: Introduction. Crown, Winchester 1991: 126 pp.

[6] Krankenhaus Umschau [Hrsg.]: ku-Sonderheft Bundespflegesatzverordnung '95 mit Fallpauschalen- und Sonderentgeltkatalog inkl. 1., 2. und 3. Änderungsverordnung. Stand 18.12.95. Baumann, Kulmbach 1996: 78 pp.

[7] Bundesministerium für Gesundheit und Konsumentenschutz: LKF'97 - Scoring Version 1.0. BMGK, Wien 1996.

[8] DRGfinder of 3M for HCFA-DRG and AP-DRG version 12.0; PMC grouper Rel. 5.0.

[9] I thank C. Rabinowitz of the Jefferson Medical College, Philadelphia, for having grouped my test cases with a grouper for D.S. version 4.0.

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Literaturhinweis:
Ergänzende Informationen zu diesem Thema finden Sie in:
-  Fischer: Patientenklassifikationssysteme, S. 365 ff. (ISBN 978-3-9521232-2-5)

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