Most techniques in the Define phase are not related to substantial use of statistical methods. The objective of the DEFINE phase is to bring together all parties concerned, grasp their knowledge and insights to the process involved, set a common objective and DEFINE how each party contributes(or the role each party takes) to the solving of the problem. In order not to get lost in subsequent meetings and ongoing discussion, this common objective, the contribution of each party, milestones and responsibilities need to be written down in what is known to be a Project Charter. Of course, problems with easy-to-identify causes are not subject of these kind of projects.

However, a classical visualization technique that is used in this phase and available in the qualityTools package is the pareto chart. Pareto charts are special forms of bar charts that help to separate the vital few from the trivial many causes for a given problem (e.g.the most frequent cause for a defective product). This way pareto charts visualize how much a cause contributes to a specific failure i.~e. the non-fulfillment of a requirement (nonconformity).

Suppose a company is investigating non conforming units (products). 120 units were investigated and 6 different types of defects (qualitative data) were found. The defects are named A to F. The defects data can be found in defects.

#create artificial defect data set
defects = c(rep("E", 62), rep("B", 15), rep("F", 3), rep("A", 10), rep("C",20), rep("D", 10))

paretoChart(defects)

##
## Frequency          62    20    15    10    10      3
## Cum. Frequency     62    82    97   107   117    120
## Percentage      51.7% 16.7% 12.5%  8.3%  8.3%   2.5%
## Cum. Percentage 51.7% 68.3% 80.8% 89.2% 97.5% 100.0%
##
## Frequency       62.00000 20.00000 15.00000  10.000000  10.000000   3.0
## Cum. Frequency  62.00000 82.00000 97.00000 107.000000 117.000000 120.0
## Percentage      51.66667 16.66667 12.50000   8.333333   8.333333   2.5
## Cum. Percentage 51.66667 68.33333 80.83333  89.166667  97.500000 100.0

This pareto chart might convey the message that in order to solve 68 percent of the problem 33 percent of the causes vital few (the vital few and the trivial many - 20 percent of the defects cause 80 percent of the problems) need to be subject of an investigation. Besides this use case, pareto charts are also used for visualizing the effect sizes of different factors for designed experiments ( see paretoPlot in [IMPROVE] (#/DEFINE) ).

The pareto chart method is available also as web application under webapps.r-qualityTools.org