Название: Probability and Statistical Inference
Автор: Robert Bartoszynski
Издательство: John Wiley & Sons Limited
Жанр: Математика
isbn: 9781119243823
isbn:
Example 1.6
Two persons enter a cafeteria and sit at a square table, with one chair on each of its sides. Suppose we are interested in the event “they sit at a corner” (as opposed to sitting across from one another). To construct the sample space, we let A and B denote the two persons, and then take as
Figure 1.1 Possible seatings of persons A and B at a square table.
Figure 1.2 Possible seatings of any two persons at a square table.
Figure 1.3 Possible seatings of one person if the place of the other person is fixed.
Sample spaces can be classified according to the number of sample points they contain. Finite sample spaces contain finitely many outcomes, and elements of infinitely countable sample spaces can be arranged into an infinite sequence; other sample spaces are called uncountable.
The next concept to be introduced is that of an event. Intuitively, an event is anything about which we can tell whether or not it has occurred, as soon as we know the outcome of the experiment. This leads to the following definition:
Definition 1.2.2 An event is a subset of the sample space
Example 1.7
In Example 1.1 an event such as “the sum equals 7” containing six outcomes
When an experiment is performed, we observe its outcome. In the interpretation developed in this chapter, this means that we observe a point chosen randomly from the sample space. If this point belongs to the subset representing the event
We will let events be denoted either by letters
In all cases considered thus far, we assumed that an outcome (a point in the sample space) can be observed. To put it more precisely, all sample spaces
The following examples show experiments and corresponding sample spaces with sample points that are only partially observable:
Example 1.8 Selection
Candidates for a certain job are characterized by their level
The objective might be to find selection thresholds