Subjective Probability: Definition & Examples

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  • 0:01 What Is Subjective Probability
  • 1:34 Subjective Probability…
  • 2:26 Example
  • 3:05 Lesson Summary
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Lesson Transcript
Instructor: Vanessa Botts
In this lesson, you will learn about subjective probability and how it reflects a personal belief that an event will happen rather than the result of formal calculations. We will also look at some examples.

What Is Subjective Probability?

On days when you're already running late for an appointment, do you feel there is almost a 100% chance of getting stuck in traffic? Or did you ever think there was a 50-50 chance you would be offered the job you for which you interviewed? These hunches, or predictions, illustrate the concept of subjective probability. Subjective probability is a prediction that is based on an individual's personal judgment, not on mathematical calculations.

Subjective probabilities, like the name suggests, are probabilities that come from an individual's personal judgment of an event happening - they are subjective. They differ from person to person, and because they are subjective, they can be based on a person's beliefs or other factors. As a matter of fact, an individual may use their own expertise, opinion, past experiences, or intuition to assign degrees of probability to a specific outcome.

Even though there are no mathematical calculations or proof behind this type of probability, it could be illustrated the following way:

P(X) = degree of belief that X is true

Probability, whether it's subjective or has been calculated mathematically, cannot tell us exactly that something will or will not happen; it's just a guide, and it's always between 0 and 1. A '0' probability would mean it is impossible that the event will happen, and a probability of '1' states with 100% certainty that the event will occur; therefore, probabilities should not be exactly 0 or 1 but rather something in between.

Subjective Probability In Action

Let's look at subjective probability in action. Karen loves eating tomatoes, but she finds that store-bought tomatoes often lack flavor and are very expensive. For those reasons, every summer for the past few years she has planted her own. Sadly, Karen does not have a green thumb. Actually, her thumb is more like black, so three seasons in a row she has had very little success growing this delicious fruit. Nonetheless, Karen will not give up trying, so this season she will again be planting tomatoes.

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