a. What changes to this book notational system are introduced as a function of having two groups rather than one?
 b. What are the differences between visual displays of variables such as bar charts and visual displays of descriptive statistics such as bar graphs?
 c. What is the main purpose and characteristics of the sampling distribution of the difference?
d. What is the difference between the sampling distribution of the mean (Chapter 7) and the sampling distribution of the difference?
 e. What is the difference between the standard error of the mean (Chapter 7) and the standard error of the difference?
