What is a Discrete Variable?
A variable is a quantity that has changing values. A discrete variable is a variable that can only take on a certain number of values. In other words, they don’t have an infinite number of values. If you can count a set of items, then it’s a discrete variable. The opposite of a discrete variable is a continuous variable. Continuous variables can take on an infinite number of possibilities.
What is a Discrete Variable? Examples
Some examples of discrete variables:
- Number of quarters in a purse, jar, or bank. Discrete because there can only be a certain number of coins (1,2,3,4,5…). Coins don’t come in amounts of 2.3 coins or 10 1/2 coins, so it isn’t possible for there to be an infinite number of possibilities. In addition, a purse or even a bank is restricted by size so there can only be so many coins.
- The number of cars in a parking lot. A parking lot can only hold a certain number of cars.
- Points on a 10-point rating scale. If you’re graded on a 10-point scale, the only possible values are 1,2,3,4,5,6,7,8,9, and 10.
- Ages on birthday cards. Birthday cards only come in years…they don’t come in fractions. So there are a finite amount of possibilities (presumably, about one hundred).
What is a Discrete Variable? Discrete random variables
Discrete random variables are variables that are a result of a random event. For example, the roll of a die. Discrete random variables are represented by the letter X and have a probability distribution P(X). If you flipped a coin two times and counted the number of tails, that’s a discrete random variable. It’s represented by the letter X. X in this case can only take on one of three possible variables: 0, 1 or 2 [tails].
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