Z I M - Paper 13th PCS/E Florence

Oct. 1997

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

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ABSTRACT

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:
 
 

Table 1: Tested Case Groups

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

• Most systems have different case groups for open and for laparoscopic cholecystectomy (exceptions: D.S. and HRG).
• The German and the Austrian system make also distinctions between open and laparoscopic appendectomy.
  

The compared PCSs are:

• HCFA Diagnosis Related Group (HCFA-DRG 12.0) [1]
• All Patient Diagnosis Related Group (AP-DRG 12.0) [2]
• Patient Management Categories (PMC 5.0) [3]
• Disease Staging (D.S. 4.0) [4]
• Health Resource Groups (HRG 2.0) [5]
• German Case Groups '95 [6]
• Austrian Diagnosis Groups (LDF '97) [7]

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.
 
 

Table 3: Comparison of American Cost Weights of Simple Diseases

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

  +----------------------------------------------------------------------------
  |    .    .    .    .    :    .    .   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)

  +----------------------------------------------------------------------------
  |    .    .    .    .    :    .   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