Losses depend on two random variables. The first is the number of losses that will occur in a
specified period. For example, a healthy policyholder with hospital insurance will have no losses
in most years, but in some years he could have one or more accidents or illnesses requiring
hospitalization. This random variable for the number of losses is commonly referred to as the
frequency of loss and its probability distribution is called the frequency distribution. The second
random variable is the amount of the loss, given that a loss has occurred. For example, the
hospital charges for an overnight hospital stay would be much lower than the charges for an
extended hospitalization. The amount of loss is often referred to as the severity and the probability
distribution for the amount of loss is called the severity distribution. By combining the frequency
distribution with the severity distribution we can determine the overall loss distribution.