Last edited 27 Jun 2018

Pareto analysis in construction

Pareto analysis is a statistical decision-making technique that identifies a limited number of input factors as having a greater impact on outcomes, whether they are positive or negative. It is based on the Pareto Principle, popularly known as the ‘80/20 rule’, that stipulates that 80% of the outputs result from 20% of the inputs.

The principle was developed by Vilfredo Pareto, a 19th century Italian economist and sociologist who was researching wealth distribution. He subsequently discovered the 80/20 rule applied to areas outside of economics, for example, 80% of the peas in his garden were produced by only 20% of the peapods planted.

Pareto analysis can also be used as a project management tool. For example, the majority of problems (80%) are produced by relatively few causes (20%); and 80% of the project’s benefits are delivered through 20% of the work.

Put simply, Pareto analysis shows that a disproportionate improvement can be made by ranking the various causes of a problem and allocating resources to tackling those that have the largest impact.

In construction, there may be a problem with the project programme that is the result of a large number of causes. Through observation and the collection of data, it might be determined that there are 8 causes. Pareto analysis may show that 80% of the problems result from the top 2 or 3 causes. The project management team can then plan an appropriate response, targeting resources at those 2 or 3 causes, rather than all 8.

A Pareto diagram (or chart) can be used to present the analysis, helping the project team to focus on the inputs with the greatest impact.

Inputs are listed along the horizontal ‘y’ axis in descending order of output frequency (using the cumulative percentage of the outputs), and uses a line graph to chart them. The vertical ‘x’ axis measures the frequency of the output for each input, and uses a bar graph to chart them.

In the example diagram, it can be seen that 42% of the issues are related to installation, and that three of the categories; installation, software faults, and shipping, account for 79% of the issues.