APPENDIX E, U.S EPA Facility Pollution Prevention Guide, EPA/600/R-92/088
OPTION RATING WEIGHTED
SUM METHOD
                                                                           

    The Weighted Sum Method is a quantitative method for
screening and ranking pollution prevention options.  This method
provides a means of quantifying the important criteria that
affect waste management in a particular facility.  This method
involves three steps.

1.  Determine what the important criteria are in
    terms of the program goals and constraints and the overall
    corporate goals and constraints.  Example criteria are:
       Reduction in waste quantity
       Reduction in waste hazard (e.g., toxicity, flammability,
        reactivity)
       Reduction in waste treatment/disposal costs
       Reduction in raw material costs
       Reduction in liability and insurance costs
       Previous successful use within the company
       Previous successful use in industry
       Not detrimental to product quality
       Low capital cost
       Low operating and maintenance costs
       Short implementation period with minimal disruption of
        plant operations
    The weights (on a scale of 0 to 10, for example) are
    determined for each of the criteria in relation to their
    importance.  For example, if reduction in waste treatment
    and disposal costs are very important, while previous suc-    
    cessful use within the company is of minor importance, then
    the reduction in waste costs is given a weight of 10 and the
    previous use within the company is given a weight of either
    1 or 2.  Criteria that are not important are not included or
    are given a weight of 0.

2. Each option is then rated on each criterion.  Again a scale of
0 to 10 can be used (0 for low and 10 for high).

3.  Finally, the rating of each option for a particular criterion
is multiplied by the weight of the criterion.  An option's
overall rating is the sum of the products of rating times the
weight of the criterion.

    The options with the best overall ratings are then selected
for the technical and economic feasibility analyses.  Table E-1
presents an example using the Weighted Sum Method for screening
and ranking options.

Table E-1.  Sample Calculation Using the Weighted Sum Method

ABC Corporation has determined that reduction in waste treatment
costs is the most important criterion, with a weight factor of
10.  Other significant criteria include reduction in safety
hazard (weight of 8), reduction in liability (weight of 7), and
ease of implementation (weight of 5).  Options X, Y, and Z are
then each assigned effectiveness factors.  For example, option X
is expected to reduce waste by nearly 80%, and is given a rating
of 8.  It is given a rating of 6 for reducing safety hazards, 4
for reducing liability, and because it is somewhat difficult to
implement, 2 for ease of implementation.  The table below shows
how the options are rated overall, with effectiveness factors
estimated for options Y and Z.

                                                  Ratings for each option  
Rating Criteria                                  Weight       X     Y     Z
Reduce treatment costs                           10           8     6     3 
Reduce safety hazards                             8           6     3     8 
Reduce liability                                  7           4     4     5 
Ease of implementation                            5           2     2     8 
Sum of weight times ratings                                  166   122   169

From this screening, option Z rates the highest with a score of
169.  Option X's score is 166 and option Y's score is 122.  In
this case, both option Z and option X should be selected for
further evaluation because their scores are high and close to
each other.