1.5 Numeric Data Types: Continuous and Discrete

A numeric variable is continuous when an infinite number of possible values could land in between any two known measurements.

If a person steps onto the scale in his bathroom at home, and it reads 205.7 pounds, is that his true weight?  We don’t really know this.  Perhaps he actually weighs 205.67 pounds, 205.714 pounds, or 205.721151 pounds.  If the scale only tells us the number in pounds, plus a single decimal point afterwards, we will have to settle for 205.7 as our value.  

For a continuous numeric variable, such as a person’s weight, the only limitation on the precision to which the  value is expressed is the instrument used to collect the data.   

A discrete variable’s values, on the other hand, exist only at specific intervals.  Common examples of discrete quantities are “count” variables, such as the number of people who visit Lobster Land on some particular day, the number of cans of Coca-Cola sold at Lobster Land in one season, or the number of unique attractions offered within the park.  

Do not fall into the trap of thinking that discrete variables are always expressed as integers!  Shoe sizes and hat sizes are both examples of discrete numeric variables that can take fractional values.  A person’s shoe size can be 8, 8.5, or 9.0 – but not 8.52565.  Likewise, hat sizes are often measured in increments of ⅛ of an inch.  However, there are not an infinite number of fitted hat sizes; therefore, hat sizes are a discrete numeric variable.