The subjective probability is one that is based on the individual experience . The person evaluates the possibilities and assigns the values according to the previous facts that he knows.
It is possible to link the subjective probability to a relative frequency or one guess . The subject measures the degree of probability according to the verisimilitude which gives each possible result.
Recall that, in a randomized experiment, it cannot be established with certainty whether a certain event will happen, or not, in a specific test. To the measurement of the probability that the event in question occurs can be assigned a number.
In the case of subjective probability, the estimation of the occurrence of the event is based on the intuition or in the opinion , generally derived from previous experiences . The individual analyzes the information which provides and grants a probability value to the event according to its level of belief about the event actually occurring.
It is common for someone to resort to subjective probability when referring to forecast of weather . He who is not a meteorologist nor has the possibility of interpreting scientific information from satellites can rely on his own experience to estimate how likely it is to rain in the following hours. If you express "I think there is a 90% chance that it will start raining before sunset", will be appealing to the subjective probability.
The subjective probability, in short, is a way to quantify the probability of occurrence of an event from individual factors from weighing . This resource can be useful when there is no other way to quantify that is more reliable.