Probability

Abstract

Questions about probability occur regularly in everyday conversations as well as in statistics classes. In this chapter we discuss what statisticians mean by the term probability and how we use it in statistical analyses. From the questions on page 177, you can see that the word probability has to do with the chance, or likelihood, or degree of certainty that some event will happen, and that the term is used well beyond the scope of statistics.

What is the probability that all four children in a family are girls? What is the chance that there will be two no-hitter baseball games in the same day? What is the likelihood that the lucky number in the daily double will be 71? How certain can Libby’s parents be that she will be accepted at Carleton College? What is the probability that the mean number of children in a family is 2.0 or less in a sample that comes from a population where the mean equals 4.0 children? If a voting population is split evenly between two parties, what is the probability of a sample percentage of 55% or more voting for one of the two candidates?