Statistics Definitions > Deterministic

## What is Deterministic?

**Deterministic **(from *determinism*, which means lack of free will) is the **opposite of a random event.** It tells us that some future event can be calculated exactly, without the involvement of randomness. For example, the conversion between Celsius and Kelvin is deterministic, because the formula is *not *random…it is an exact formula that will always give you the correct answer (assuming you perform the calculations correctly):

**If something is deterministic, you have all of the data necessary to predict (determine) the outcome with 100% certainty.**The process of calculating the output (in this example, inputting the Celsius and adding 273.15) is called a

**deterministic process**or procedure. A few more examples:

- Rolling a fair die: each number on a six-sided die has the same odds (1/6) of coming up.
- Calculating what your savings account balance will be in a month (add up your deposits and the prevailing interest rate).
- The relationship between a circumference and radius of a circle, or the area and radius of a circle.

On the other hand, a **random event** or process can’t be determined with an exact formula. You can ballpark it, or “hazard a good guess,” but you can’t assign probabilities to it. For example, the odds of seeing a black cat on your way to work tomorrow cannot be calculated, as the process is completely random, or *stochastic*. You could take a good guess (zero probability would be a good start), but it would still be just that — a guess.

## Deterministic Relationships

In simple linear regression, if the response and explanatory variables have an exact relationship, then that relationship is deterministic. In other words, if you can predict with 100% certainty where a y-value is going to be based only on your x-value, then that’s a deterministic relationship.

## Statistical Relationships

Most things in real life are a mixture of random and deterministic relationships. For example, weather patterns are partly random, and they can *partly *be forecast. When something is part random and part deterministic, it’s called a **statistical relationship** or **probabilistic relationship**. Both terms mean the same thing; Which you use is a matter of personal preference.

**Related article:** Deterministic Functions.