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FOUNDATIONAL and APPLIED STATISTICS for BIOLOGISTS USING R This page intentionally left blank FOUNDATIONAL and APPLIED STATISTICS for BIOLOGISTS USING R Ken A. Aho Idaho State University Pocatello, Idaho, USA Cover: View east from the Abiathar Peak in Northeastern Yellowstone National Park. Three mountain goats (Oreom- nos americanus) are visible at the edge of the summit plateau. Goat weights are approximately normally distributed with mean 90.5 kg and variance 225 kg2. This distribution is shown in the lower right hand corner of the cover. A ran- dom sample from this distribution is shown in the strip at the top. Photo credit: Scott Close. Goat illustration donated by Pearson Scott Foresman (an educational publisher) to Wikimedia Commons, http://commons.wikimedia.org/wiki/ Category:Pearson_Scott_Foresman_publisher; http://all-free-download.com. 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Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com To JEF and OAA who traveled on this journey This page intentionally left blank Contents Preface ........................................................................................................................................... xix Acknowledgments ...................................................................................................................... xxi Section I Foundations . 1 Philosophical and Historical Foundations ........................................................................3 1.1 Introduction ...................................................................................................................3 1.2 Nature of Science ..........................................................................................................3 1.3 Scientic Principles .......................................................................................................4 1.3.1 Objectivity .........................................................................................................4 1.3.2 Realism ..............................................................................................................4 1.3.3 Communalism ..................................................................................................5 1.4 Scientic Method ..........................................................................................................5 1.4.1 A Terse History ................................................................................................6 1.4.1.1 Experimentation ..............................................................................8 1.4.1.2 Induction ...........................................................................................8 1.4.1.3 Probability ........................................................................................8 1.5 Scientic Hypotheses ...................................................................................................9 1.5.1 Falsiability ......................................................................................................9 1.6 Logic .............................................................................................................................. 10 1.6.1 Induction ......................................................................................................... 10 1.6.2 Deduction ........................................................................................................ 11 1.6.3 Induction versus Deduction ......................................................................... 11 1.6.4 Logic and Null Hypothesis Testing ............................................................12 1.6.4.1 Modus Tollens ................................................................................12 1.6.4.2 Reductio Ad Absurdum ............................................................... 13 1.7 Variability and Uncertainty in Investigations ........................................................ 14 1.8 Science and Statistics .................................................................................................. 16 1.9 Statistics and Biology .................................................................................................. 16 1.10 Summary ...................................................................................................................... 18 Exercises .................................................................................................................................. 18 2. Introduction to Probability ................................................................................................. 21 2.1 Introduction: Models for Random Variables........................................................... 21 2.1.1 Set Theory Terminology ...............................................................................23 2.1.2 Philosophical Conceptions of Probability .................................................. 24 2.2 Classical Probability ...................................................................................................26 2.2.1 Disjoint ............................................................................................................28 2.2.1.1 Boole’s Inequality ..........................................................................30 2.2.2 Independence ................................................................................................. 31 2.2.2.1 Bonferroni’s Inequality ................................................................. 31 2.3 Conditional Probability ..............................................................................................32 vii viii Contents 2.4 Odds ..............................................................................................................................34 2.4.1 Odds Ratio and Relative Risk ......................................................................34 2.5 Combinatorial Analysis .............................................................................................35 2.5.1 Multiplication Principle ................................................................................35 2.5.2 Permutations ...................................................................................................36 2.5.3 Combinations .................................................................................................37 2.6 Bayes Rule ....................................................................................................................38 2.7 Summary ......................................................................................................................43 Exercises ..................................................................................................................................43 3. Probability Density Functions ...........................................................................................49 3.1 Introduction .................................................................................................................49 3.1.1 How to Read This Chapter ...........................................................................50 3.1.2 So, What Is Density? ......................................................................................50 3.1.3 Cumulative Distribution Function ..............................................................52 3.2 Introductory Examples of pdfs .................................................................................54 3.2.1 Discrete pdfs ...................................................................................................55