# Random variable and approximately gamma distribution

Characteristic function There is no simple expression for the characteristic function of the F distribution. It can be expressed in terms of the Confluent hypergeometric function of the second kind a solution of a certain differential equation, called confluent hypergeometric differential equation. How long do we need to wait until a customer enters our shop? How long will it take before a call center receives the next phone call? How long will a piece of machinery work without breaking down?

Questions such as these are frequently answered in probabilistic terms by using the exponential distribution. All these questions concern the time we need to wait before a given event occurs.

If this waiting time is unknown, it is often appropriate to think of it as a random variable having an exponential distribution.

## Parameterizations

Roughly speaking, the time we need to wait before an event occurs has an exponential distribution if the probability that the event occurs during a certain time interval is proportional to the length of that time interval. More precisely, has an exponential distribution if the conditional probability is approximately proportional to the length of the time interval comprised between the times andfor any time instant.

In many practical situations this property is very realistic. This is the reason why the exponential distribution is so widely used to model waiting times.

## Relationships among probability distributions - Wikipedia

The exponential distribution is strictly related to the Poisson distribution. If 1 an event can occur more than once and 2 the time elapsed between two successive occurrences is exponentially distributed and independent of previous occurrences, then the number of occurrences of the event within a given unit of time has a Poisson distribution.

We invite the reader to see the lecture on the Poisson distribution for a more detailed explanation and an intuitive graphical representation of this fact.In statistics, the gamma distribution is the distribution associated with the sum of squares of independent unit normal variables and has been used to approximate the distribution of positive definite quadratic forms (i.e.

those having the form) in multinormally distributed variables. The gamma distribution has also been used in many other. Apr 14,  · An Introductory Guide in the Construction of Actuarial Models: A preparation for the Actuarial Exam C/4 - Ebook download as PDF File .pdf), Text File .txt) or read book online. In particular, if Z ∼ Gamma (a, 1), then the random variable X = G-1 It is interesting to note that the Γ-EW pdf can also be approximately symmetric depending on the parameter values.

## 4 Gamma Distribution

It is worth emphasizing that the Weibull distribution, EE distribution, gamma Weibull. Practice Exams 5 Let Y be a random variable having the density function f given by f(y) = y/2 for 0 distribution function of Y.

The random variable is also sometimes said to have an Erlang ashio-midori.com Erlang distribution is just a special case of the Gamma distribution: a Gamma random variable is also an Erlang random variable when it can be written as a sum of exponential random variables.

is the confluent hypergeometric function. Consider now the sum of more than two gamma random variables. In this case, an exact theoretical discrete distribution of (k, w k) 0, 1, 2, does not exist and an approximation is ashio-midori.com this end, let us consider the first moment.

Seeing Theory - Probability Distributions