Percentages

In: Business and Management

Submitted By mlcs1943
Words 24786
Pages 100
PERCENTAGES: THE MOST USEFUL STATISTICS EVER INVENTED

Thomas R. Knapp

©

2010

"Eighty percent of success is showing up."
- Woody Allen

“Baseball is ninety percent mental and the other half is physical.”
- Yogi Berra

"Genius is one percent inspiration and ninety-nine percent perspiration."
- Thomas Edison

Preface

You know what a percentage is. 2 out of 4 is 50%. 3 is 25% of 12. Etc. But do you know enough about percentages? Is a percentage the same thing as a fraction or a proportion? Should we take the difference between two percentages or their ratio? If their ratio, which percentage goes in the numerator and which goes in the denominator? Does it matter? What do we mean by something being statistically significant at the 5% level? What is a 95% confidence interval? Those questions, and much more, are what this book is all about.

In his fine article regarding nominal and ordinal bivariate statistics, Buchanan (1974) provided several criteria for a good statistic, and concluded: “The percentage is the most useful statistic ever invented…” (p. 629). I agree, and thus my choice for the title of this book. In the ten chapters that follow, I hope to convince you of the defensibility of that claim.

The first chapter is on basic concepts (what a percentage is, how it differs from a fraction and a proportion, what sorts of percentage calculations are useful in statistics, etc.) If you’re pretty sure you already understand such things, you might want to skip that chapter (but be prepared to return to it if you get stuck later on!).

In the second chapter I talk about the interpretation of percentages, differences between percentages, and ratios of percentages, including some common mis-interpretations and pitfalls in the use of percentages.

Chapter 3…...

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