Statistics for Six Sigma Green Belts with Minitab and JMP

3.1. Graphing Attribute Data

When you have attribute data, you tally responses into categories and determine the frequency or percentage in each category. Two widely used graphs, the bar chart and the Pareto diagram, will be discussed.

The Bar Chart

A bar chart presents each category of an attribute type variable as a bar whose length is the frequency or percentage of values falling into a category. The data in Table 3.1 represent a summary table of the number of errors and the type of error for laboratory tests.

Table 3.1. Summary Table for Causes of Defects in Laboratory Tests

Cause	Frequency	Percentage
Social Security Number	226	49.8
Name	71	15.6
Date of Birth	58	12.8
Test	44	9.7
Doctor	39	8.6
Others	16	3.5
Total	454	100.0
LABTESTS
Source: Extracted from N. B. Riebling, ...