The PARETO Procedure

Example 15.8 Creating Weighted Pareto Charts

Note: See Pareto Analysis Based on Cost in the SAS/QC Sample Library.

In many applications, you can quantify the priority or severity of a problem by using a measure such as the cost of repair or the loss to the customer expressed in man-hours. This example shows how to analyze such data by using a weighted Pareto chart that incorporates the cost.

Suppose that the cost associated with each of the problems in data set Failure5 (see Example 15.6) has been determined and that the costs have been converted to a relative scale. The following statements add the cost information to the data set:

data Failure5;
   length Analysis $ 16;
   label Analysis = 'Basis for Analysis';
   set Failure5;
   Analysis = 'Cost';
      if      Cause = 'Contamination'  then Cost = 3.0;
      else if Cause = 'Metallization'  then Cost = 8.5;
      else if Cause = 'Oxide Defect'   then Cost = 9.5;
      else if Cause = 'Corrosion'      then Cost = 2.5;
      else if Cause = 'Doping'         then Cost = 3.6;
      else if Cause = 'Silicon Defect' then Cost = 3.4;
      else                                  Cost = 1.0;
      output;
   Analysis = 'Frequency';
      Cost = 1.0;
      output;
run;

The classification variable Analysis has two levels, Cost and Frequency. For Analysis=Cost, the value of Cost is the relative cost, and for Analysis=Frequency, the value of Cost is one.

The following statements use Analysis as the classification variable to create a one-way comparative Pareto chart in which the cells are weighted Pareto charts that use Cost as the weight variable:

ods graphics off;
goptions vsize=4.25 in htext=2.8 pct htitle=3.2 pct;
title 'Pareto Analysis By Cost and Frequency';
proc pareto data=Failure5;
   vbar Cause / class      = ( Analysis )
                freq       = Counts
                weight     = Cost
                barlabel   = value
                out        = Summary
                intertile  = 1.0;
run;

The display is shown in Output 15.8.1.

Output 15.8.1: Taking Cost into Account


Within each cell, the height of a bar is the frequency of the category multiplied by the value of Cost, expressed as a percentage of the total across all categories. Thus, for the cell in which Analysis is equal to Frequency, the bars simply indicate the frequencies expressed in percentage units. This display shows that the most commonly occurring problem (contamination) is not the most expensive problem (oxide defect). The output data set Summary is listed in Output 15.8.2.

Output 15.8.2: Summary Output Data Set

Pareto Analysis By Cost and Frequency

Obs Analysis Cause Cost _COUNT_ _WCOUNT_ _PCT_ _CMPCT_
1 Cost Oxide Defect 9.5 86 817.0 58.6799 58.680
2 Cost Contamination 3.0 110 330.0 23.7018 82.382
3 Cost Metallization 8.5 11 93.5 6.7155 89.097
4 Cost Silicon Defect 3.4 17 57.8 4.1514 93.249
5 Cost Corrosion 2.5 16 40.0 2.8729 96.122
6 Cost Doping 3.6 10 36.0 2.5856 98.707
7 Cost Miscellaneous 1.0 18 18.0 1.2928 100.000
8 Frequency Oxide Defect 1.0 86 86.0 32.0896 32.090
9 Frequency Contamination 1.0 110 110.0 41.0448 73.134
10 Frequency Metallization 1.0 11 11.0 4.1045 77.239
11 Frequency Silicon Defect 1.0 17 17.0 6.3433 83.582
12 Frequency Corrosion 1.0 16 16.0 5.9701 89.552
13 Frequency Doping 1.0 10 10.0 3.7313 93.284
14 Frequency Miscellaneous 1.0 18 18.0 6.7164 100.000