5.2.2: Types of Probability


Classical probability (also called Mathematical Probability) is determined by counting or by using a mathematical formula or model.

Example

The probability of getting a "Heads" when tossing a fair coin is 0.5 or 50%. The probability of rolling a 5 on a fair six‐sided die is 1/6, since all numbers are equally likely.

Empirical probability is based on the relative frequencies of historical data, studies or experiments.

Example

The probability that Stephen Curry make a free throw is 90.8% based on the frequency of successes from all prior free throws.

The probability of a random student getting an A in a Statistics class taught by Professor Nguyen is 22.8%, because grade records show that of the 1000 students who took her class in the past, 228 received an A.

In a study of 832 adults with colon cancer, an experimental drug reduced tumors in 131 patients. The probability that the experimental drug reduces colon cancer tumors is 131/832, or 15.7%.

Subjective probability is a “one‐shot” educated guess based on anecdotal stories, intuition or a feeling as to whether an event is likely, unlikely or “50‐50”. Subjective probability is often inaccurate.

Example

Although Robert is nervous about retaking the Statistics course after dropping the prior quarter, he is 90% sure he will pass the class because the website ratemyprofessor.com gave the instructor very positive reviews.

Jasmine believes that she will probably not like a new movie that is coming out soon because she is not a fan of the actor who is starring in the film. She is about 20% sure she will like the new movie.

No matter how probability is initially derived, the laws and rules of probability will be treated the same.

5.2.2: Types of Probability is shared under a CC BY-SA license and was authored, remixed, and/or curated by LibreTexts.