In collecting data concerning the characteristics of a group or individuals or objects, such as the heights and weights of students in a university or the numbers of defective and non defective bolts produced in a factory on a given day, it is often impossible or impractical to observe the entire group, especially if it is large. Instead of examining the entire group called the population, or universe, one examines a small part of the group , called a sample.
For the probability section, makes a fine (simpler) complement to Ross' 'A First Course in Probability'. Provides, as in Ross, many exercises but in a different style. The rest of the book is about regression including an interesting chapter on time series.