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Aggregating the benefits using the additive model 43
Closeness to
customers
100
80
Best
0 Worst
Visibility Image Size Comfort Car
parking
Best
Worst
Best
Worst
Best
Worst
Best
Worst
Best
Worst
Figure 3.5 – Derivation of swing weights. For example, a swing from the worst to the
best location for visibility is considered to be 80% as important as a swing from the worst
to the best location for closeness to customers
sub-attributes. Any inconsistencies between the two sets of weights can
then be discussed and, hopefully, resolved.
Aggregating the benefits using the additive model
We now have (1) a measure of how well each office performs on each
attribute and (2) weights which enable us to compare the values allocated
to one attribute with the values allocated to the others. This means that
we are now in a position to find out how well each office performs
overall by combining the six value scores allocated to that office.
To do this, we will assume that the additive model is appropriate. As
we show below, this simply involves adding an office’s weighted value
scores together to obtain a measure of the overall benefits which that
office has to offer. The additive model is by far the most widely used,
but it is not suitable for all circumstances. In particular, the model is
inappropriate where there is an interaction between the values associated
with some of the attributes. For example, when choosing a house,
an attractive architecture and a pleasant garden may complement each
other, leading to a combined value which is greater than the sum of
the individual values. We will examine the limitations of the additive
model later.
The calculations which the additive model involves are shown below
for Addison Square. Each value is multiplied by the weight attached to