Last edited 01 Sep 2021

Analytic Hierarchy Process AHP

AHPDecisionMaking.jpg

Contents

[edit] Introduction

The analytic hierarchy process (AHP - or analytical hierarchy process) is a form of multi-criteria decision making (MCDM) that applies mathematics and psychology to the selection process - with minimal bias - when no clear choice is apparent. AHP can help to identify the most beneficial solution using a systematic approach that ranks different options based on importance.

AHP was developed in the 1970s by Thomas Saaty, a university professor who specialised in statistics and operations research. Along with AHP, Saaty created two other decision-making approaches - the Analytic Network Process or ANP (for decisions that depend on feedback) and Neural Network Process or NNP (which incorporates the mathematics of ANP and applies neural firing and synthesis).

[edit] Overview

AHP takes a problem and examines it in three phases:

  1. The goal. What issue needs to be resolved?
  2. The solutions. What are all of the available alternatives?
  3. The criteria. What criteria will be used to judge the possible solutions?

After phase three has been determined, it is then possible to calculate an importance weighting for each criterion. This is achieved through pairwise comparisons, a method of analysis that evaluates two criteria at the same time rather than comparing several criteria at once. Pairwise comparisons make it easier to select the most appropriate choice once the utility factor has been calculated. Utility is defined as a numerical representation of how useful or beneficial something is.

[edit] Addressing the calculation process

Linear algebra is a type of mathematics that can be used along with pairwise comparisons to prioritise the criteria, based on the weight of its importance. Criteria with higher numbers are seen as more important.

Despite being technically valid and practically useful, AHP has been criticised for its reliance on mathematics. However, basic AHP calculations can be performed by readily available tools such as Excel. More advanced software is also available to automate the process.

To assist in the calculation process, Saaty created a sample nine-point scale, which is reproduced in the study, Analytic Hierarchy Process-Based Construction Material Selection for Performance Improvement of Building Construction: The Case of a Concrete System Form.

Definition Intensity of importance
Equally important 1
Moderately more important 3
Strongly more important 5
Very strongly more important 7
Extremely important 9
Intermediate values 2, 4, 6, 8

[edit] Applying AHP

Because AHP is designed to assist in the analysis of complex situations, it has been used in business, manufacturing and other industries. Rather than prescribing a "correct" decision, AHP helps decision makers find one that best suits their values and their understanding of the problem.

For this reason, AHP is sometimes used in engineering, construction management, portfolio management, facilities maintenance, material selection and other important situations. In the US, engineers used an AHP rating system to prioritise maintenance projects for thousands of public structures, including nearly 3,000 bridges in need of repair.

As a material selection tool, AHP is designed to look beyond a product’s price or life cycle while removing conflicting or biased evaluation criteria based on less quantifiable factors such as personal preference or previous experience. Instead, it helps make selections based on qualitative properties such as performance.

[edit] Critique of AHP

Arroyo, Tommelein and Ballard (2014) offered a critique of AHP in a paper in the Journal of Construction Engineering and Management. They suggested that Choosing by Advantages (CBA) is preferable to AHP at least in the context of detailed design.

CBA:

  1. provides a more context-based analysis than AHP,
  2. does not incorporate conflicting judgments for weighing factors as AHP does,
  3. does not assume linear trade-offs between factors as AHP does,
  4. does not assume that factors have zero as a natural scale as AHP does,
  5. focuses on differentiating between alternatives more than AHP,
  6. maintains the result of the decision when non-differentiating factors are removed, whereas AHP may not, and
  7. defers subjective judgments until late in the decision-making process, whereas AHP requires expressing them earlier.

CBA is now being used in UK by Highways England and the East Thames Crossing project among others.

For more on CBA see e.g.

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[edit] External resources

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