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AHP OVERVIEW

It builds a hierarchy of decision items using comparisons between each
pair of items expressed as a matrix. Paired comparisons produce weighting
scores that measure how much importance items and criteria have with each
other.

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Step 1: Developing a Model

It creates a hierarchy to analyse the Decision.

 

 

 

 

 

 

 

 

Here, the model consists of three levels. First level is our ultimate
goal of this process i.e. Selection of Technology; second level contains
different criteria which are used to select technology and they are cost
effectiveness, impact on construction industry, constructability, safety,
adoptability, maintenance and reduction in greenhouse gases; third level
contains alternatives available i.e. solar roads or kinetic roads.

This hierarchical model helps to better understand the problem, criteria
to be worked upon and alternatives available.

 

Step 2: Deriving Priorities for the criteria

We have 7 criteria in total and they might have different priorities
relative to each other. So, in this step relative priority or in other word
weights of each criterion are obtained.

For this, pairwise comparison of each criterion is done using an AHP
calculator developed by K. D. Goepel. Linear Saaty scale is used to do
comparison which is 1-9 intensity scale.

 

Intensity

Definition

Explanation

1

Equal Importance

Two elements contribute equally to the objective

3

Moderate Importance

Experience and judgement slightly favour one element over another

5

Strong Importance

Experience and judgement strongly favour one element over another

7

Very strong importance

One element is favoured very strongly over another

9

Extreme importance

The evidence favouring one element over another is of the highest
possible order of affirmation

2,4,6,8 can be used to express intermediate values

Table :-Saaty scale for AHP

 

This calculator was used to take responses from 20 respondents who have
given their view on this comparison based on their judgements and preferences.
The result is as shown below:-

Sr. No.

Criteria

Weight

Rank

1

Cost effectiveness

 

 

2

Impact on construction industry

 

 

3

Constructability

 

 

4

Safety

 

 

5

Adoptability

 

 

6

Maintenance

 

 

7

Reduction in greenhouse gases

 

 

Table :- Weights of criteria

 

Step 3:- Consistency

It is very important to check consistency of responses. Consistency is
illustrated in the following example: If A is preferred over B twice and B is
preferred over C thrice then A should be preferred over C 6 times. Hence, if
values other than 6 are inserted than it will show some inconsistency. AHP
allows some level of inconsistency as the judgements are subjective.
Consistency ratio is used to measure consistency. Consistency ratio less than
10% is acceptable and if it is greater than 10% than inputs need to be revised.
Here, we have calculated consistency ratio of each respondent and they are
within acceptable limit.

 

Step 4:- Deriving local priorities for the alternatives

This step aims to find priorities of alternatives with respect to each
criterion i.e. cost effectiveness, impact on construction industry,
constructability, safety, adoptability, maintenance and reduction in greenhouse
gases. These priorities are determined with respect to each specific criterion
and hence are known as local priorities.

For this purpose, pairwise comparison is done of all alternatives with
respect to specific criterion. Here also consistency ratio needs to be
calculated, but as we have only two alternatives, consistency check is not
required.

Results are shown below

 

Step 5:- Derive overall priorities (Model Synthesis)

We have calculated local priorities of each alternative with respect to
each criterion but also these criteria have different weights. So, this needs
to be combined to calculate overall priorities. This step is also known as
model synthesis.

A table is formed as shown below which has weights of each criterion and
priorities of alternatives with respect to each criterion.

Criteria

Weight

Solar (Alternative
1)

Kinetic (Alternative
2)

Cost effectiveness

 

 

 

Impact on construction industry

 

 

 

Constructability

 

 

 

Safety

 

 

 

Adoptability

 

 

 

Maintenance

 

 

 

Reduction in greenhouse gases

 

 

 

 

 

 

 

Table :- Overall Priorities

Finally, overall priorities are obtained by doing sum product of weights
of criteria and priorities of alternatives.

 

Step 6:- Sensitivity Analysis

What-if analysis is done to see how the results would have changed if the
weights of criteria were different. This is known as sensitivity analysis. This
is done to check the what are the drivers in determining the overall
priorities.

For e.g. What if all the criteria have same weights. Result will be as
follows.

Criteria

Weight

Solar (Alternative
1)

Kinetic (Alternative
2)

Cost effectiveness

0.143

 

 

Impact on construction industry

0.143

 

 

Constructability

0.143

 

 

Safety

0.143

 

 

Adoptability

0.143

 

 

Maintenance

0.143

 

 

Reduction in greenhouse gases

0.143

 

 

 

Total

 

 

Table :- Overall priorities
if all the criteria have same weights

As we can see that overall priorities has been changed to .

 

Step 7:- Making a Final Decision

It is now possible to make a decision i.e. Technology can be selected out
of solar and kinetic.

For this overall priorities are compared and checked whether there is a
significant difference in overall priorities to make a choice. Here, we can
make clear decision based on overall priorities and i.e. Kinetic Roads should
be selected.

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