## 1.6 Mr. $$X$$

When evaluating something of practical interest, you usually look at long names. Consider the variable

$$X$$: ‘number of children of women treated at a public hospital in 2020’

This long description will bore any text that uses it many times, making it impractical to carry out calculations involving such characteristic of interest or random variable. It is reasonable, therefore, to associate long descriptions with symbols. The letter $$X$$ is famous for symbolizing something generic, both in Science and in everyday life. Note that the symbol used to separate $$X$$ from its description is :, not =.

In this text, $$X$$ (uppercase) will be used to represent the characteristic of interest or random variable, and $$x_k$$ (lowercase) to represent the $$k$$th observed value of this characteristic. Thus, while $$X$$ generically represents the number of children of women treated at a public hospital in 2020, $$x_4 = 2$$ indicates that the fourth woman evaluated in the study has two children. 