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32 Decisions involving multiple objectives: SMART
We start constructing the tree by addressing the attributes which
represent the general concerns of the decision maker. Initially, the
owner identifies two main attributes, which he decides to call ‘costs’ and
‘benefits’. There is, of course, no restriction on the number of attributes
which the decision maker can initially specify (e.g. our decision maker
might have specified ‘short-term costs’, ‘long-term costs’, ‘convenience
of the move’ and ‘benefits’ as his initial attributes). Nor is there any
requirement to categorize the main attributes as costs and benefits. In
some applications (e.g. Wooler and Barclay 6 ) ‘the risk of the options’ is
an initial attribute. Buede and Choisser 7 describe an engineering design
application for the US Defense Communications Agency, where the
main attributes are ‘the effectiveness of the system’ (i.e. factors such
as quality of performance, survivability in the face of physical attack,
etc.) and ‘implementation’ (i.e. manning, ease of transition from the old
system, etc.).
Having established the main attributes for our business owner, we
need to decompose them to a level where they can be assessed. The
owner identifies three main costs that are of concern to him: the annual
rent, the cost of electricity (for heating, lighting, operating equipment,
etc.) and the cost of having the office regularly cleaned. Similarly,
he decides that benefits can be subdivided into ‘potential for improved
turnover’ and ‘staff working conditions’. However, he thinks that he will
have difficulty assessing each office’s potential for improving turnover
without identifying those attributes which will have an impact on
turnover. He considers these attributes to be ‘the closeness of the office
to potential customers’, ‘the visibility of the site’ (much business is
generated from people who see the office while passing by) and ‘the
image of the location’ (a decaying building in a back street may convey a
poor image and lead to a loss of business). Similarly, the owner feels that
he will be better able to compare the working conditions of the offices
if he decomposes this attribute into ‘size’, ‘comfort’ and ‘car parking
facilities’.
Having constructed a value tree, how can we judge whether it is an
accurate and useful representation of the decision maker’s concerns?
Keeney and Raiffa 3 have suggested five criteria which can be used to
judge the tree:
(i) Completeness. If the tree is complete, all the attributes which are of
concern to the decision maker will have been included.
(ii) Operationality. This criterion is met when all the lowest-level attributes
in the tree are specific enough for the decision maker to