Approaches to Probability | CFA® Level 1 Exam

Probability Formula: No. of Times Event Occurred / Total No. of Observations

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Question

Which approach to probability is exemplified by the following formula?

Prob. of Event happening = No. of times event occurred in the past/Total no. of observations.

Answers

Explanations

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A. B. C. D.

C

When we based the probability on the number of times the events has occurred in the past over the total number of observations, we are using the relative frequency approach.

The approach to probability exemplified by the given formula is the relative frequency approach, which is represented by answer choice C.

The relative frequency approach is based on empirical observations and relies on past data to estimate the probability of an event occurring. In this approach, the probability of an event happening is determined by dividing the number of times the event occurred in the past by the total number of observations or trials.

The formula provided in the question demonstrates this approach. It calculates the probability of an event happening by dividing the number of times the event occurred in the past by the total number of observations. This ratio represents the relative frequency of the event occurring based on historical data.

For example, let's say we want to determine the probability of flipping a coin and getting heads. If we have observed the coin being flipped 100 times in the past, and heads appeared 50 times, we can use the relative frequency approach to estimate the probability. By applying the formula, we would calculate the probability as 50 (number of times event occurred in the past) divided by 100 (total number of observations), resulting in a probability of 0.5 or 50%.

The relative frequency approach is commonly used in practice, especially when dealing with situations where the underlying probability distribution is not known or difficult to determine. By relying on past observations, this approach provides an empirical estimate of the probability based on historical data, which can be useful in decision-making and risk assessment.