Contents -- 1. Introduction -- 2. Do Vitamin C and Other Antioxidants Benefit Health? Using Observational and Experimental Studies to Test Medical Hypotheses -- 3. Can Police Dogs Identify Criminal Suspects by Smell? Using Experiments to Test Hypotheses about Animal Behavior -- 4. Why Are Frogs in Trouble? Complementary Observations and Experiments to Test Hypotheses in Ecology -- 5. How Do Animals Find Stored Food? Strong Inference by Testing Alternative Hypotheses -- 6. What Causes Cancer? The Complexities of Causation -- 7. Why Do We Age? Different Levels of Causation as Complementary Explanations -- 8. How Does Coffee Affect Health? Combining Results of Multiple Studies -- 9. How Will Climate Change Affect the Spread of Human Diseases? Models and the Perils of Prediction -- 10. Conclusion: How Science Works and Its Role in Society -- Appendix 1. Using Data for Twins to Estimate Genetic and Environmental Contributions to the Risk of Cancer -- Appendix 2. Precision and the Power of Statistical Tests -- Notes -- References -- Index -- A -- B -- C -- D -- E -- F -- G -- H -- I -- J -- K -- L -- M -- N -- O -- P -- Q -- R -- S -- T -- U -- V -- W -- Y -- Z.