Six Sigma Tool Navigator: The Master Guide for Teams

Tool description

A frequency distribution can display in table format quantitative (class intervals) as well as qualitative (categories) data organized in a meaningful order. The FD is often used to group data for histogram, pie chart, or other tools.

Typical application

• To determine how data is distributed over an acceptable range of upper and lower limits.

• To sort and group raw data.

• To show distribution ratios (percent).

Problem-solving phase

Typically used by

before

• Checksheet

• Observation

• Data collection strategy

• Surveying

• Interview technique

after

• Histogram

• Line Chart

• Pie Chart

• Two-directional Bar Chart

• Trend Analysis

Notes and key points

Preparation for Grouping of Data

• Determine the range(s) of the distribution

  R = (H-L) +1

• For smaller data sets, N = < 100: number of class intervals (C.I.) between 5-10

• For larger data sets, N = > 100: number of class intervals (C.I.) between 10-20.

• Width of the class interval to be 2, 3, 5, 10, 20 for smaller numbers. (Add zeros for larger data sets.)

• Select number of class intervals:

• Check if the lowest data point in the data set is divisible an equal number of times as those by the C.I. width. If not, select the next lower data point that is.

Step-by-step procedure

• STEP 6 Insert prepared data into the FD table. See example Customer Complaints per Day (quantitative data). Date the table.

  Note

  For categorical data, construct a FD table as shown in example for customer response data.

Example of tool application

Customer Complaints per Day