What is Experimental Probability?
Experimental probability is the probability of an event based on actual results from an experiment or observation. Rather than being calculated from theory or logic, it is determined by repeating a process and recording how often a specific outcome occurs.
This type of probability answers the question: “How often did this outcome happen when we actually tried it?”
How to Find Experimental Probability
Use this formula to calculate it:
Experimental Probability = (Number of times the event occurred) ÷ (Total number of trials)
It is especially useful when the theoretical probability does not exist or is unknown, too difficult to calculate, or when you want to see how closely real-world outcomes match expected ones.
If a theoretical probability exists for a particular scenario, the experimental probability often differs from it, especially when the number of trials is small. However, as the number of trials increases, the experimental value tends to approach the theoretical value (when one exists). This principle is known as the law of large numbers.
Example
A wildlife researcher observes a group of 80 birds to see how many fly away when a person approaches within 10 feet. Out of the 80 birds, 34 fly away. The likelihood that a bird flies away when approached is:
34 ÷ 80 = 0.425, or 42.5%
This experimental probability is based on what actually occurred during the observations and would likely vary with different groups, locations, or conditions. There’s no simple theoretical expectation here, so the experimental value provides the best available estimate.
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