Tool 69: Dot Diagram

AKA

Dot Plot

Classification

Analyzing/Trending (AT)

Tool description

A dot diagram tool allows data to be displayed for quick analysis. Observations of some sets of numbers are dotted along a scale to indicate a natural tendency to form a normal (bell-shaped) distribution, or to show clustering around a central value. It can also be used to check for patterns in recorded data.

Typical application

• To display the relationship or distance between the numbers (observations) in a small sample or population of numbers (≤30).

• To provide quick measurements of range and average, and to show the dispersion of data.

Problem-solving phase

→	Select and define problem or opportunity
→	Identify and analyze causes or potential change
	Develop and plan possible solutions or change
	Implement and evaluate solution or change
	Measure and report solution or change results
	Recognize and reward team efforts

Typically used by

1	Research/statistics
	Creativity/innovation
	Engineering
	Project management
	Manufacturing
	Marketing/sales
	Administration/documentation
	Servicing/support
3	Customer/quality metrics
	Change management

links to other tools

before

• Data Collection Strategy

• Sampling Methods

• Observation

• Checksheet

• Surveying

after

• Stem-and-Leaf Display

• Problem Analysis

• Monthly Assessment Schedule

• Descriptive Statistics

• Demographic Analysis

Notes and key points

• A dot diagram should not be used for more than 30 observations.

• Numbers that are off the scale should be reported as outliers.

Step-by-step proceudre

• STEP 1 Collect and record data. Sort values (numbers) from low to high. See example Recorded Lost Calls.

• STEP 2 Draw a horizontal line and mark or scale units of measurement, as shown in the example.

• STEP 3 Place a dot for each value (number) and continue until all numbers have been dotted. When finished dotting, the dot diagram displays all values and how often they occurred.

• STEP 4 If desired, basic statistical analysis can be completed as shown.

Example of tool application