Bar charts and Pareto chart

Bar charts and Pareto chart

Pareto principle

Two charts which can be used for data analysis are a bar chart and a Pareto chart.

Bar chart

A graphical display showing variation of a data set (e.g. length, attitudes, costs) that is plotted as bars. The graphic presentation makes it easier to see relationships.

Typically it is used:

  • To determine which cause dominates
  • To aid understanding the distribution of occurrences of different problems, causes, consequences and so on.

Histogram


Pareto charts

A Pareto chart is a series of bars whose heights reflect the frequency or impact of problems. Bars are arranged in descending order of height from left to right. The bars on the left are considered relatively more important than those on the right.

The Pareto principle postulates that most effects, often 80%, are the result of a small number of causes, 20%. The Pareto principle would suggest that if the vital 20% of causes (those bars on the left) are dealt with, the effects should be reduced by 80%.

The chart may help to identify the biggest contributors and therefore get the most improvement from the valuable resources available. A Pareto chart shows the causes of a problem arranged by degree of severity, expressed in terms of frequency, costs and so on.

Typical use:

  • To obtain a clearer picture of the set of causes by viewing them according to importance
  • To help understand which causes need / needed further investigation

Good to use:

  • When the process being investigated produces data that are broken down into categories, and the number of times each category occurs can be counted
  • To help set priorities regarding problems to investigate that may have contributed to the root cause

Pareto chart