Tool 79: Fox Index

AKA

Gunning Fog Index

Classification

Changing/Implementing (CI)

Tool description

Developed by Robert Gunning, the fog index stands for the reading level required to understand written information. Computing the fog index allows a writer to assess at what reading level he or she is currently writing and what adjustments, if any, are needed to write for a particular audience.

Typical application

• To determine a reading level requirement for one's writing.

• To estimate an educational level needed to understand written information.

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

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

links to other tools

before

• Audience analysis

• Surveying

• Questionnaires

• Cluster analysis

• Starbursting

after

• Thematic content analysis

• Case study

• Critical incident

• Presentation

• Storyboarding

Notes and key points

• Calculating Robert Gunning's Fog Index:

  F.I. = 0.4 (A + B)

  Where:	.4	=	A constant
  	A	=	Average number of words per sentence
  	B	=	Number of words with three or more syllables

Step-by-step procedure

• STEP 1 Take a random sample of 100 to 200 words of written material.

• STEP 2 Count the number of sentences found in the sample.

  Note

  Independent clauses are counted as sentences.

• STEP 3 Divide the total number of words in the sample by the number of sentences. This will result in the average number of words per sentence. See example Using these Written Process Steps.

• STEP 4 Identify and count the number of words having three or more syllables.

  Note

  Exclude words that may qualify because of -es, -ed, -ing, or words that are capitalized or compounded.

• STEP 5 Add the totals of Step 3 and Step 4 above and multiply the total by 0.4 to get the fog index. This result identifies the level of reading ability one should have to understand these written process steps.

Example of tool application

Using These Written Process Steps

Sample: This tool's process steps numbers 1-5

Total number of words = 127

Total number of sentences = 10

-Average number of words per sentence = 12.7

Total number of words having three or more syllables = 13

F.I. = 0.4 (12.7 + 13)

F.I. = 10.3