Thus, while S l has a larger expected value than S 3 , its standard deviation is
greater, therefore the uncertainty associated with its aggregate score is also higher;
therefore the larger the confidence level sought, the less attractive S l becomes
relative to S 3 .
15.6 Allocating Weights to the Decision Criteria
The allocation of weightages to the constituent criteria is central to the working of
the additive model. The reason behind the weights is to signify the relative importance of each selected decision criterion with respect to all others. A number of basic
techniques exist for calculating criterion weightings within the additive model. All
require input of judgements from the decision-makers. The following methods are
outlined below:
• Presumption of equal weights
• Ranking system for obtaining weights
• Ratio system for obtaining weights
• Basic pairwise analysis
• Resistance-to-change grid
15.6.1 Presumption of Equal Weights
If the decision-makers are not in a position to assign weights to the criteria, or are
unwilling to do so, the process can proceed initially on the basis that all criteria are
treated as being of equal importance, with each attribute given an equal weight. In
these circumstances, it is particularly important to carry out an extensive sensitivity
analysis to gauge the effect of varying the weightings away from their equal
valuations on the baseline performances of the project options.
15.6.2 Ranking System for Obtaining Weights
This procedure requires the decision maker to carry out an initial ranking of the
criteria in according to importance. Each criterion is then allocated a score depending
on its rank, with the one ranked first assigned the score ‘1’, the one ranked second
assigned the score ‘2’, and so on. In the case of criteria tying for the same rank, an
average score is assigned to them. For example, take the case where one criterion is
ranked first and assigned the score ‘1’. Three criteria are ranked equal second. Their
score is obtained by averaging the three scores ‘2’, ‘3’ and ‘4’. Each criterion will
thus be given the score ‘3’. The criterion ranked below these three in fifth place will
15.6 Allocating Weights to the Decision Criteria
427
greater, therefore the uncertainty associated with its aggregate score is also higher;
therefore the larger the confidence level sought, the less attractive S l becomes
relative to S 3 .
15.6 Allocating Weights to the Decision Criteria
The allocation of weightages to the constituent criteria is central to the working of
the additive model. The reason behind the weights is to signify the relative importance of each selected decision criterion with respect to all others. A number of basic
techniques exist for calculating criterion weightings within the additive model. All
require input of judgements from the decision-makers. The following methods are
outlined below:
• Presumption of equal weights
• Ranking system for obtaining weights
• Ratio system for obtaining weights
• Basic pairwise analysis
• Resistance-to-change grid
15.6.1 Presumption of Equal Weights
If the decision-makers are not in a position to assign weights to the criteria, or are
unwilling to do so, the process can proceed initially on the basis that all criteria are
treated as being of equal importance, with each attribute given an equal weight. In
these circumstances, it is particularly important to carry out an extensive sensitivity
analysis to gauge the effect of varying the weightings away from their equal
valuations on the baseline performances of the project options.
15.6.2 Ranking System for Obtaining Weights
This procedure requires the decision maker to carry out an initial ranking of the
criteria in according to importance. Each criterion is then allocated a score depending
on its rank, with the one ranked first assigned the score ‘1’, the one ranked second
assigned the score ‘2’, and so on. In the case of criteria tying for the same rank, an
average score is assigned to them. For example, take the case where one criterion is
ranked first and assigned the score ‘1’. Three criteria are ranked equal second. Their
score is obtained by averaging the three scores ‘2’, ‘3’ and ‘4’. Each criterion will
thus be given the score ‘3’. The criterion ranked below these three in fifth place will
15.6 Allocating Weights to the Decision Criteria
427