A value of a variable is the actual number recorded for a particular person or object. A quantitative variable is one that takes numerical values for which the operations of arithmetic make sense. A qualitative variable is one that simply records into which of several categories a person or thing falls. It is an empirical fact that values of most variables encountered in the real world exhibit some variability . For example, if we measure the heights of ten students in the class, we will most likely get ten diiferent values.
Variability is an inherent aspect of our world .
Since variation is present in virtually every set of data, we should seek to understand the nature of variation. In fact, understanding the nature and magnitude of variation are critical to sound statistical reasoning. It combines numerical calculation with graphical displays to compress, summarize, and describe data clearly. The pattern of variation of a variable is called its distribution . A distribution records the numerical values of a variable and how often each value occurs.