How would you explain the analysis of variance

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How would you explain the analysis of variance, assuming that your audience has not had a statistics class before?
This is the textbook I am using.

Textbook Statistics for Health Care Research: A Practical Workbook Grove, S. (2007). Statistics for health care research: A practical workbook. St. Louis, MO: Saunders Elsevier. ISBN-13: 9781416002260