Skydiving, anyone? A humor piece published in the British Medical Journal (Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomized control trials, Gordon, Smith, and Pell, BMJ, 2003:327) notes that we cant tell for sure whether parachutes are safe and effective because there has never been a properly randomized, double-blind, placebo-controlled study of parachute effectiveness in skydiving. (Yes, this is the sort of thing statisticians find funny. . . .) Suppose you were designing such a study: a) What is the factor in this experiment? b) What experimental units would you propose?8 c) What would serve as a placebo for this study? d) What would the treatments be? e) What would the response variable be? f) What sources of variability would you control? g) How would you randomize this experiment? h) How would you make the experiment double-blind?

Chapter 15 Inferences for Regression Chapter 4 was all descriptive statistics (describing the relationship between Y and X in the sample data) and Chapter 15 is inferential statistics (describing the ‘true’ relationship between Y and X in the population) The first few pages of Chapter 15 have two main purposes: o To introduce the population regression model o Briefly review what we did with regression in Chapter 4 The population model is x . The text does a good job of explaining this model. Y 0 1 The population mean of Y has a linear relation with X. 0 is the population Y-intercept and 1Is the population slope Our sample regression equation statistics (ŷ, b O and b 1 will provide estimates of the p