Weighting Techniques Used In Environmental Studies

Ranking

Nominal group process Rating

Predefined importance scale Multiattribute utility measurement Unranked paired comparison Ranked paired comparison Delphi tive order of importance. If n decision factors exist, rank ordering involves assigning 1 to the most important factor, 2 to the second-most important factor, and so forth, until n is assigned to the least important factor. The rank order numbers can be reversed; that is, n can be assigned to the most important factor, n — 1 to the second-most important factor, and so forth, until 1 is assigned to the least important factor. The Nominal Group Process (NGP) technique (Voelker 1977) illustrates a ranking technique and is described next.

The NGP technique is an interactive group technique and was developed in 1968 (Voelker 1977). It was derived from social-psychological studies of decision conferences, management-science studies of aggregating group judgments, and social work studies of problems surrounding citizen participation in program planning. The NGP technique is widely used in health, social service, education, industry, and government organizations. For example, Voelker (1977) describes use of the NGP technique to rank decision factors in siting nuclear power plants. The following four steps are involved in the NGP technique for importance weighting:

1. Nominal (silent and independent) generation of ideas in writing by a panel of participants

2. Round-robin listing of ideas generated by participants on a flip chart in a serial discussion

3. Group discussion of each recorded idea for clarification and evaluation

4. Independent voting on priority ideas, with mathematical rank ordering determining the group decision

Rating techniques for importance weighting basically involve assigning importance numbers to decision factors and sometimes their subsequent normalization via a mathematical procedure. Two examples of rating techniques are the use of a predefined importance scale (Linstone and Turoff 1978) and the use of the multi-attribute utility measurement (MAUM) technique (Edwards 1976). The NGP technique can also be used for rating the importance of decision factors. Decision factors can be assigned numerical values based on predefined importance scales. Table 2.5.3 delineates five scales with definitions to consider in assigning numerical values to decision factors (Linstone and Turoff 1978). Use of the predefined scales can aid in systematizing importance weight assignments.

Paired comparison techniques (unranked and ranked) for importance weighting involve comparisons between decision factors and a systematic tabulation of the numerical results of the comparisons. These techniques are used extensively in decision-making efforts, including numerous examples related to environmental impact studies. One of the most useful techniques is the unranked paired comparison technique developed by Dean and Nishry (1965). This technique, which can be used by an individual or group, compares each decision factor to each other decision factor in a systematic manner.

TABLE 2.5.3 EXAMPLE OF IMPORTANCE SCALE (LINSTONE AND TUROFF 1978)

Scale Reference

Definitions

1. Very important

A most relevant point

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